Rico Colibri: Driving Under the Influence White Paper

8/2/2019 Rico Colibri: Driving Under the Influence White Paper

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WHITE PAPER RELATIVE TO HB 1261

ON

DRIVING UNDER THE INFLUENCE OF CANNABIS (DUIC)

PRESENTED TO

THE

MEMBERS OF THE COLORADO SENATE JUDICIARY COMMITTEE

By

Rico Colibri

Representing

The Association of Cannabis Trades for Colorado



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CONTENTS

Introduction p. 3

Summary p. 4

Abstract p. 7

Survey of Scientific Research p. 8

Driving, Impairment & Culpability Studies p. 8

Alcohol and Cannabis p. 9

Concerns and Recommendations p. 10

Citations p. 13

THC Concentrations p. 13

Impairment Citations p. 15

Driving Citations p. 18

Culpability Citations p. 20



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INTRODUCTION

First and foremost ACT4CO applauds the legislature’s positive step forward in considering a

legal blood limit for THC. We thank Representatives Levy and Waller for their efforts. You

have been doing your homework and we recognize the need for appropriate standards.

That said, there are many published scientific studies of which the legislators may not be aware

that cast considerable doubt on the 5 nanogram per milliliter (5 ng/ml) standard as a presumption

of impaired driving.

The abstract and survey of scientific research that follow will provide you with a very complete

overview of the current state of science that supports our concerns and recommendations. For

those of you interested in delving more deeply into the research, we have included references to

the citations identified in the narrative.



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SUMMARY

DRIVING UNDER THE INFLUENCE (DUI) & MEDICAL MARIJUANA

House Bill 1261 (HB 1261) would set a standard of 5 nanograms of THC per milliliter (5ng/ml)

of whole blood as the point at which an individual would be automatically (per se) considered to

be DUI. Theoretically, this standard equates to a blood alcohol content (BAC) of .08 however,

many studies suggest 5ng/ml equates to .05 BAC.

The bill seeks to define an unambiguous “bright line” for law enforcement and the public in

determining when a person’s THC level constitutes impairment. The 5ng/ml standard would be a

“per se” or irrefutable evidence that a citizen was impaired while driving.

The problem is that the science supporting the 5ng/ml standard is not conclusive as there is

evidence to support a higher number such as 8ng/ml especially when recent use is combined with

latent levels.

The Science

Although THC blood levels can be an indicator or impairment, it is not infallible. According to

a 2004 National Highway Traffic Safety Administration study, “it is not possible to conclude

anything about a driver’s impairment on the basis of his/her plasma concentrations of THC …

determined by a single sample.” The study goes on to state that: “ It is inadvisable to try and

predict effects based on blood THC concentrations alone.…”

The primary reason for this difficulty is that medical marijuana patients using cannabis

frequently for chronic issues such as pain, cancer, MS, and glaucoma have a higher latent THClevel than those using cannabis for more intermittent or lower level pain management. Another

reason is that variations in body chemistry or body mass index can result in wide differences in

impairment with the same proportion of THC to blood.

In a March 10, 2011 email to Mr. Colibri, Mr. Grotenhermen stated: “Usually regular users, who

have not recently used cannabis, have a THC concentration of about 4 to 8 ng/ml in blood serum,

which is about 2 to 4 ng/ml in whole blood. Thus, a limit of 5 ng/ml THC in whole blood would

protect most medicinal users. However, very heavy users may have concentrations above this

limit.” Mr. Grotenhermen’s study is the basis for the 5ng/ml concept.

In another study, Dr. Barry Beyerstein of Simon Frazer University concluded that “The

relationship between THC levels in blood and impairment of eye-hand coordination, reaction

time and other components of driving skill is not a straightforward one. Also, individual

differences of impairment among different users are so great that it would be very difficult to set

a fair legal standard of impairment that would apply to everyone.”

Moreover, the more than150 independent driving experiments on the impact of cannabis on



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essential skills for driving under laboratory and road conditions revealed that cannabis may

impair some driving skills. However, results varied considerably and some of the skills tested

were not impaired at doses as high as 18 mg of THC. “Under the influence of marijuana, drivers

are aware of their impairment, and when the experimental task allows it, they tend to actually

decrease speed, avoid passing other cars, and reduce other risk-taking behaviors.” Another study

in 2010 by Anderson et. al. found that being under the influence of active cannabis, subjects “did

not appear to affect their [participants’] driving”.

Driving studies consistently find that cannabis leads to a more cautious style of driving, whereas

alcohol leads to a more risky style of driving. No controlled epidemiological evidence has ever

clearly connected the use of cannabis alone to an increase in culpability for traffic fatalities or

injuries resulting in hospitalization any more than a drug free driver. A 1994 study by Robbe et.

al. concluded, "Of the many psychotropic drugs, licit and illicit, that are available and used by

people who subsequently drive, cannabis may well be amongst the least harmful. Campaigns to

discourage the use of cannabis by drivers are certainly warranted. But concentrating a campaign

on cannabis alone may not be in proportion to the safety problem it causes."

It is important to note that most of these studies sought to “prove” impairment at lower levels of

THC concentrations in blood.

On the other hand, the data clearly shows alcohol impairs far more than cannabis and the

combination of cannabis and alcohol together causes greater impairment than either alone.

The Concerns

Given the preponderance of inconclusive scientific data, it is clear that the 5ng/ml standard is not

appropriate for everyone. In an email from the author of one of the foundational studies, henoted that latent THC in a patient using cannabis to control chronic conditions could range from

2ng/ml to 4ng/ml days to a week later. With latent levels such as these, the 5ng/ml limit appears

too low and will unnecessarily subject Colorado citizens to arrest and involuntary blood tests at

great expense to the state regardless of whether the person has passed or failed a field sobriety

test.

While law enforcement officials insist that “probable cause” is required prior to a stop, that cause

may be anything from walking out of a medical marijuana center, driving with a broken light, to

erratic driving behavior. In other words, probable cause can range from the miniscule to the

major and be upheld in court. On stopping an individual, law enforcement may ask if a citizenhas a medical marijuana card and that may be used as justification for requiring a blood test

regardless of any supposed impairment or dangerous driving.

The Recommendations

The Association of Cannabis Trades for Colorado supports the need for an appropriate DUI bill

for cannabis provided it is fair and has a sound basis in science and experience. No one wants



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people driving while they are impaired whether it is from alcohol, prescription drugs or cannabis.

On behalf of medical marijuana patients throughout the state, The Association of Cannabis

Trades for Colorado is making four very practical proposals to the state legislature:

1. Law enforcement and prosecutors should show that the driver's performance is actually

cannabis-impaired in order to get a DUI conviction. This should be a rebuttable presumption of impairment, not the proposed per se standard.

2. We recommend 5 ng/ml of active THC as the basis for DWAI (Driving While Ability

Impaired), and 8 ng/ml of active THC for DUI which would parallel the .05/.08 BAC.

3. Inasmuch as the science supports levels higher than 5 ng/ml, we recommend an automatic

sunset review of two years to ensure that whatever standard is adopted is reevaluated in light of

experience and data.

4. We also recommend that medical marijuana patients with medical documentationsupporting levels higher than the proposed standard be afforded an affirmative defense.



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ABSTRACT

• Although THC blood levels can be an indicator of impairment, it is not infallible.

• Driving studies consistently find that cannabis leads to a more cautious style of driving,

whereas alcohol leads to a more risky style of driving.

•Dr. Barry Beyerstein stated “individual differences of impairment among different usersare so great that it would be very difficult to set a fair legal standard of impairment that

would apply to everyone."

• No controlled epidemiological evidence has ever clearly connected the use of cannabis

alone to an increase in culpability for traffic fatalities or injuries resulting in

hospitalization any more than a drug free driver.

• The Grotenhermen study, which is the foundation for the 5 ng/ml recommended limit,

must be understood in its proper context. Dr. Franjo Grotenhermen of the German nova-

Institut wrote. "The presentation of the results in the abstract is somewhat misleading.

The figures for the unadjusted odds ratios suggest a more than threefold risk increase for

all THC positive drivers and a more than twofold increase even for drivers with a THC

blood concentration of less than 1 ng/ml. However, closer review of the results shows that

two other factors contributed to the higher accident risk, i.e., alcohol consumption and

the younger age of the THC positive drivers, compared to the whole cohort .”

• Researchers at the French National Institute for Research on Transportation and Safety

found that “alcohol intoxication and speeding were nearly ten times more likely to be an

attributing factor in traffic fatalities than the use of cannabis.”

• Our concerns on the proposed 5 ng/ml limit relates to the latent whole blood levels of

THC resulting from chronic use. Patients using marijuana in compliance with state law

would most often test positive for that THC level although not be impaired.

• We respectfully request the definition of blood be “whole blood” and THC as “Delta-9-

THC” specifically excluding other non-psychoactive cannabinoids and metabolites such

as THC-COOH.

• Law enforcement and prosecutors should show that the driver's performance is actually

cannabis-impaired in order to get a DUIC conviction. This should be a rebuttable

presumption, not the proposed per se standard.

• ACT4CO asks you to please consider adopting a set of two legal limits for the

concentration of “active THC” in “whole blood” equivalent to the one in place for

alcohol under Colorado law i.e DWAI & DUI. We recommend 5 ng/ml of active THC asthe basis for DWAIC (Cannabis), and 8 ng/ml of active THC for DUIC. We recommend

setting the limit as a rebuttable presumption, not a per se limit.

• Inasmuch as the science supports levels higher than 5 ng/ml but is still not conclusive, we

recommend an automatic sunset review of two years to ensure that whatever standard is

adopted is reevaluated in light of experience and data. We also recommend that medical

marijuana patients with medical documentation supporting levels higher than the



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proposed standard be afforded an affirmative defense.



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SURVEY OF SCIENTIFIC RESEARCH

Driving, Impairment & Culpability Studies

Although THC blood levels can be an indicator of impairment, it is not infallible. [10] According to the National Highway Traffic Safety Administration study "it is not possible to conclude

anything about a driver's impairment on the basis of his/her plasma concentrations of THC and

THC-COOH determined in a single sample.” [1][2]

Patients tend to prefer potent strains to extend the duration of relief. [11][12] Thus a single

generic limit that encompasses both occasional and chronic use is at best inappropriate. [13]

THC concentrations do not directly imply impairment because chronic use diminishes the effects

of THC. [14] Multiple studies have concluded that long-term use creates physiological changes

such as CB1 receptor down regulation. [15][16][17][18] Chronic medical marijuana users can

safely drive with elevated ng/ml blood levels of THC, even immediately after use. [19][20]

In one study an ADHD patient's driving was improved after using cannabis, where tests revealed

71 ng/ml in serum, which roughly equates to 35 ng/ml in whole blood. [21] Additionally, the

results of a study on how cannabis impairs driving in Britain claimed, “The results of our test

clearly show that a small or moderate amount of cannabis is actually quite beneficial to

someone's driving performance." [22] The vast amount of studies listed in the attached

references do not support a rigid ng/ml limit, and suggest even larger doses of cannabis do not

impair performance and may actually improve driving for medical and non-medical users alike.

[23][24]

Dr. Barry Beyerstein stated “individual differences of impairment among different users are so

great that it would be very difficult to set a fair legal standard of impairment that would apply to

everyone." [28] The main sources of evidence concerning THC ng/ml limits with respect to

driving and accident risk are derived from driving experiments and Epidemiological data. A

driving study in 2010, which took both gender and the modern potency of cannabis into account

found “Under the influence of marijuana, participants decreased their speed and failed to show

expected practice effects during a distracted drive. No differences were found during the baseline

driving segment or collision avoidance scenarios.” [29] Furthermore the Highway Traffic Safety

Administration concluded, “THC’s adverse effects on driving performance appear relatively

small.” [30]

The body of driving experiments offers an alternative viewpoint to deriving per se limits for

THC. 150 independent driving studies on the impact of cannabis on essential skills for driving

under laboratory and road conditions, revealed that cannabis may impair some driving skills

However, results varied considerably and some of the skills tested were not impaired at doses as

high as 18 mg of THC. “Under the influence of marijuana, drivers are aware of their impairment,

and when the experimental task allows it, they tend to actually decrease speed, avoid passing



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other cars, and reduce other risk-taking behaviors.”. [31] Anderson et al. 2010 found that being

under the influence of active cannabis, subjects “did not appear to affect their [participants’]

driving” and observed “many teenagers and young adults driving under the influence of

marijuana are doing so while… talking on the cell phone and/or text messaging others”. [32]

This is noteworthy in light of evidence that text messaging can be worse than drunk driving. In

another study police officers rated drivers with a BAC of 0.08% as more impaired than thosewho had taken moderate to high doses of cannabis, and driving instructors rated subjects with a

BAC of 0.04% as impaired, while those who had consumed a dose equivalent to 7 mg THC were

rated as unimpaired. The estimated THC per joint would be approximately 8 mg.

Driving studies consistently find that cannabis leads to a more cautious style of driving, whereas

alcohol leads to a more risky style of driving. [33][34] Epidemiological studies examine the

actual culpability of a driver under the influence of cannabis causing an accident, relative to that

of a drug free driver under similar conditions. That relative risk is expressed as odds ratio (OR).

An OR greater than 1 corresponds to an increase in risk.

Drummer et al. conducted an epidemiological study that correlated THC concentrations in whole

blood and accident risk that met quality criteria not met by other studies. The study found that

“THC concentrations in whole blood in the range of 0–5 ng/ml were associated with an OR of

0.7.” [47] The data found that THC concentrations in whole blood are not associated with an

elevated risk (OR > 1) until they exceed 6 ng/ml. Bear in mind that 1 correlates with a gradually

increasing accident risk. Comparison of cannabis-induced risks to those associated with alcohol-

induced risks yields an approximation to a numerical per se limit for DUIC/BAC of 0.05%

alcohol. This is an OR of about 1.5–2 that corresponds to a THC concentration in whole blood

of about 6–8 ng/ml.

No controlled epidemiological evidence has ever clearly connected the use of cannabis alone to

an increase in culpability for traffic fatalities or injuries resulting in hospitalization any more

than a drug free driver. It has even been suggested that cannabis use may actually reduce those

risks. [35][36][37][38][39][40][41]

The Grotenhermen study, which is the foundation for the 5 ng/ml recommended limit, must be

understood in its proper context. Dr. Franjo Grotenhermen of the German nova-Institut wrote.

"The presentation of the results in the abstract is somewhat misleading. The figures for the

unadjusted odds ratios suggest a more than threefold risk increase for all THC positive drivers

and a more than twofold increase even for drivers with a THC blood concentration of less than 1

ng/ml. However, closer review of the results shows that two other factors contributed to the

higher accident risk, i.e., alcohol consumption and the younger age of the THC positive drivers,

compared to the whole cohort .” [43]

Alcohol and Cannabis



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However, the data clearly shows alcohol impairs far more than cannabis and the combination of

cannabis and alcohol together causes greater impairment than either alone. [25][26] The

Grotenhermen et al. 2007 study which is the most cited to support a 5 ng/ml limit of THC in

whole blood suggests that limit roughly equates to a BAC of .05% which is not per se DUI under

Colorado law, and that limit is often taken out of context. [27]

Researchers at the French National Institute for Research on Transportation and Safety foundthat “alcohol intoxication and speeding were nearly ten times more likely to be an attributing

factor in traffic fatalities than the use of cannabis.”[44] Ramaekers et al. 2004 supports both of

the previous studies by stating “Experimental studies have shown alcohol and THC combined

can produce severe performance impairment even when given at low doses.” [45]

We close our culpability findings with the results of the Robbe study, which, like many other

studies before concluded: "Of the many psychotropic drugs, licit and illicit, that are available and

used by people who subsequently drive, cannabis may well be amongst the least harmful.

Campaigns to discourage the use of cannabis by drivers are certainly warranted. But

concentrating a campaign on cannabis alone may not be in proportion to the safety problem itcauses" [46]

In summary, Blood levels of THC are principally related to how recently or often cannabis is

used, and not directly related to impairment. The problem with trying to link THC levels to

impairment is that unlike alcohol, THC concentrations in the blood have no clear correlation to

activity in the brain. A1999 study commissioned by Drug Czar General McCafrey demonstrated

cannabis does not affect people with traumatic neuropathic illness such as MS the same. These

patients do not feel the same euphoria as people who do not have these conditions. The safety of

medical drivers is affirmed by the FDA approved package insert for Marinol. The insert states

that driving and operating heavy equipment after use of marinol (synthetic THC) is permissible if

patients can tolerate the effects. This is pure Synthetic THC without any CBD, a cannabinoid that

mitigates the effects of THC. [48] Medical Marijuana would actually have a less euphoric effect

as it contains CBD. Marinol is far more dysphoric than cannabis, but driving is permissible for

tens of thousands of drivers using Marinol with the approval of the FDA. In defense of the 5 ng/

ml limit, the fact that 1 in 5 drivers involved in accidents in Colorado test positive for THC is

being thrown around. This is because THC_COOH metabolites can remain in the body for 30

days and shows up in toxicology reports on car accidents, which supports the need for proper

testing.

CONCERNS AND RECOMMENDATIONS

Our concerns on the proposed 5 ng/ml limit relates to the latent whole blood levels of THC

resulting from chronic use. Patients using marijuana in compliance with state law, would most

often test positive for that THC level although not be impaired. However, we understand the



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what level in the blood active marijuana will cause you to be impaired. It is around eight

nanograms per milliliter of blood. THC stays in the blood a long time so it's not fair to punish

them for when they're not impaired, so we’re looking for that scientifically proven threshold,”

says Washington State Senator Goodman.

We are including a copy of this bill for your review. We ask you to please couple the proposed

dual limits with an affirmative defense for medical patients who may have higher ng/ml levelssuch as MS patients. With DUI per se charges, it does not matter what a citizen’s driving pattern

is like, or whether the driver passes field sobriety tests, it is a charge that is based purely on body

chemistry. Recall for a moment the ADHD patient who tested at 35 ng/ml of THC, but his

driving had improved.

Law enforcement and prosecutors should show that the driver's performance is actually cannabis-

impaired in order to get a DUIC conviction. The driver's guilt should be determined by the

totality of evidence in the case: driving behavior, performance on roadside sobriety tests, the

driver's conduct, the smell of smoke in the car and also whole blood test results.

The protocol should be erratic driving supported by evidence such as odor, drowsiness, failure of

and/or refusal to cooperate with a field sobriety test and then the testing at either 5ng/ml

(combined with alcohol?) and or 8 ng/ml per se, unless the driver has a pre-existing medical

condition and thus an affirmative defense.

ACT4CO's suggested limits avoids unnecessary testing of patients who may test positive at the

proposed 5 ng/ml DUIC, when not impaired. Which could place a financial and logistical burden

on law enforcement and taxpayers. As there is strong science to support a successful defense to a

5 ng/ml DUIC charge with respect to patients and even non medical users. Denied accurate

testing coupled with a low 5 ng/ml DUIC per se charge, courts could become bogged down by

drivers taking their cases to trial to maintain driving privileges when DUIC per se charges are atthe lower 5 ng/ml standard.

We are also concerned about how long a driver could be detained. We have heard of a story

where a patient was detained over night. This has no basis in science; it takes approximately 2-3

hours for your blood THC concentration to fall below 5 ng/ml after smoking cannabis. So drivers

should not be detained longer than 3 hours, if arrested. In Idaho, blood samples are being

forcibly taken by officers in the field.

ACT4CO would prefer to see sanctions rather than traumatizing procedures such as forced blood

samples on a possibly physically impaired patient that could result in injuries from a clash of personalities between an upset driver and a frustrated officer. A driver who refuses or fails a field

sobriety test should be required to submit to a blood test by a trained medical professional or risk

criminal and administrative sanctions. We have heard additional concerns that a few biased

officers could target patients and or MMC owners as the leave centers. MMC owners could be

cited as having low moral character if they were charged with a DUIC and lose their businesses.

Putting a system in place to report such abuses would resolve these concerns.



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Given the invasiveness of blood tests and the inadequacy of urine tests in determining

impairment. ACT4CO urges the legislature to consider exploring less traumatic methods such as

saliva testing. THC concentrations in saliva appear to correlate reasonably well with THC

concentrations in blood, and saliva testing may emerge as a non-invasive screening test for the

use of cannabis in road checks, which could be confirmed by blood analysis. To our knowledge,

Australia currently implements Saliva testing. Developing a modified field sobriety test which

measures the behavior of drivers (reaction time, for example) rather than their blood could also be a low cost pre blood or saliva test solution.

Thank you for hearing our concerns and ACTing on behalf of patients.

Sincerely, ACT4CO

Please feel free to contact me with any questions or concerns [email protected]



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CITATIONS

THC CONCENTRATIONS

[1] (F. Grotenhermen, et al., "Testing for Impairment by Cannabis," 2004.) Need to specify

whole blood testing in the bill.

"When reporting THC levels in blood or adopting legal limits one must always specify the

reference fluid … For THC, concentrations measured in whole blood are typically 1.6–2.2 times

lower than those measured in blood or plasma."

[2] (National Highway Traffic Safety Administration) This is in reference to what cannabinoids

are being tested for, active vs. inactive.

“Chronic users can have mean plasma levels of THC-COOH of 45 ng/ml, 12 hours after use;

corresponding THC levels are, however, less than 1 ng/mL.”

[3] (National Highway Traffic Safety Administration) Supports both the limitations of THC ng/

ml limits and especially using metabolites.

“It is inadvisable to try and predict effects based on blood THC concentrations alone, and

currently impossible to predict specific effects based on THC-COOH concentrations”

[4] (Clinical Chemistry 55: 2180-2189, 2009. First published October 15, 2009; 10.1373/

clinchem.2008.122119) Accuracy of testing is a concern.

“Our data indicate that total cannabinoid concentrations are not currently measurable due to thelack of cannabinoid sulfate and 11-OH-THC glucuronide standards. Total concentrations cannot

be estimated by GC-MS analysis because enzymatic and/or alkaline hydrolysis fails to fully

cleave cannabinoid conjugates and/or produces poor chromatography for accurate cannabinoid

measurement. A third problem is that stability of THC-, 11-OH-THC-, and THCCOOH-

glucuronides and sulfates at refrigerated and frozen storage temperatures have not been

adequately characterized in authentic plasma specimens. Thus, limitations of current research

methods are underestimation of cannabinoid glucuronide conjugates owing to incomplete

hydrolysis by E. coli β-glucuronidase and instability when stored at 4 ¡C for approximately 2

weeks.”

[5] (National Highway Traffic Safety Administration) Supports THC concentrations do not imply

impairment and are dependant on use patterns.

“It is difficult to establish a relationship between a person's THC blood or plasma concentration

and performance impairing effects. Concentrations of parent drug and metabolite are very

dependent on pattern of use as well as dose.”



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[6] (Clinical Chemistry 55: 2180-2189, 2009. First published October 15, 2009; 10.1373/

clinchem.2008.122119) THC from chronic use can be released into the body slowly over time.

“Prolonged THC excretion in frequent cannabis users suggests that low free or hydrolyzed

plasma THC concentrations, such as 1–2 µg/L (per se THC concentrations), may not reflect

recent cannabis exposure. Prolonged daily cannabis use may extend detection times due to THC

tissue accumulation and slow release into blood.”

[7] (Huestis MA, Henningfield JE, Cone EJ. Blood cannabinoids. I. Absorption of THC and

formation of 11-OH-THC and THCCOOH during and after smoking marijuana. J Anal Toxicol

1992;16:276-282) (Karschner EL, Schwilke EW, Lowe RH, Darwin WD, Pope HG Jr, Herning

R, et al. Do 9-tetrahydrocannabinol concentrations indicate recent use in chronic cannabis users?

Addiction 2009 Oct 5]..) Shows how long THC can remain in the system without use.

“Chronic heavy cannabis use prolongs blood cannabinoid detection intervals. After acute

smoked cannabis in occasional users, blood THC was generally below detection limits within 12

h. After frequent use, mean whole blood THC was >1 µg/L (n = 5) after 1 week of monitored

abstinence.”

[8] (Karschner EL, Schwilke EW, Lowe RH, Darwin WD, Pope HG Jr, Herning R, et al. Do 9-

tetrahydrocannabinol concentrations indicate recent use in chronic cannabis users? Addiction

[Epub ahead of print 2009 Oct 5].) Supports latent whole blood THC levels with chronic use.

“The Kraschner EL study concuded “Substantial whole blood THC concentrations persist

multiple days after drug discontinuation in heavy chronic cannabis users. It is currently unknown

whether neurocognitive impairment occurs with low blood THC concentrations, and whether

return to normal performance, as documented previously following extended cannabis

abstinence, is accompanied by the removal of residual THC in brain. These findings also may

impact on the implementation of per se limits in driving under the influence of drugs legislation.”

[9] (Grotenhermen et al. 2007) Supports 3 ng/ml base levels for patients resulting from multiple

uses per day.

“The slow disappearance of THC from serum is particularly pronounced with heavy users, who

consume more than one marijuana cigarette (joint) per day, or even with moderate users of

cannabis. Their blood may contain THC concentrations of between 1.0 and 6.4 ng/ml serum even

24–48 hours after smoking the last joint”.

[10] (Grotenhermen et al. 2007) Supports latent THC levels do not imply impairment.

“limits by design penalize the presence in body fluids of an active drug ingredient or its

metabolites, which does not necessarily correspond to actual impairment. This is a particular

concern with cannabis. Its main psychoactive constituent, delta-9-tetrahydrocannabinol (THC), is

detectable in blood for up to 2 days. Depending on the frequency of use, its metabolites are

detectable in blood and urine for days or weeks after cannabis use.”



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[11] (UK TRL Cannabis and driving: a review of the literature and commentary No.12) Shows

that THC's effects fade in a short period after use and the dose ratio is arbitrary.

“The study estimates 11 ng/ml THC as the equivalent dose to the legal limit of alcohol (0.08%

BAC in the UK). Complicating this assessment is the fact that cannabis effects on driving fade

after a short period of time, while THC may be present in the body for weeks.”

[12] (US Department of Transportation, 2003. op. Cit.) Supports siting the ratio of ng/ml within

one hour of use and how that reflects on impairment.

“Experimental research on the effects of cannabis … indicat[e] that any effects … dissipate

quickly after one hour.”

[13] (UK TRL Cannabis and driving: a review of the literature and commentary No.12) Supports

11 ng/ml as being equivalent to .08% BAC and that even this ratio should not always apply to

medicinal use of cannabinoids.

“Much of the interest in cannabis as a potential accident risk factor is related to the concernabout alcohol. Both alcohol and cannabis have an intoxicating effect that alters the psychological

state of the individual. However, the mechanism of action and form of intoxication of these drugs

are distinct. Alcohol may provide a useful metric to evaluate the effect of cannabis. Moreover,

given the existence of a set legal limit for alcohol, research of the dose equivalence between

alcohol and cannabis for performance relevant to accident risk may provide a method of

determining a safety critical limit for cannabis. German research based on meta-analyses has

concluded that 50% of performance is impaired at 11ng/ml THC, making this an equivalent level

of intoxication to 0.08% BAC, although more recent and driving specific studies need to be

compared with respect to effect size to confirm these suggested dose equivalences.However, it is

important not to use parallel reasoning between alcohol and cannabis to dictate the researchagenda and transport policy for cannabis alone. Such reasoning is particularly inappropriate for

medicinal applications of cannabis derivatives.”

IMPAIRMENT CITATIONS

[14] (Bedard et al. 2007) Science does not support exact THC concentrations relating to

impairment.

“Consideration needs to be given to evidence that THC serum concentration does no always

denote impairment.”

[15] (D'Souza et al. 2008; Hart et al. 2001; Jones et al. 1981; Ramaekers et al. 2009) THC does

not effect chronic users the same as occasional users.

“Previous research has demonstrated that daily cannabis users are less sensitive to the impairing

effects of Δ9 tetrahydrocannabinol (THC) intoxication on cognitive and psychomotor functions.”



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[16] (Gonzalez et al. 2005) Suggests that long term use creates physiological changes to offset

effects.

“This loss of sensitivity or tolerance to the behavioral effects of THC after prolonged use is

believed to result from a change in pharmacodynamic response as evinced by CB1 receptor

downregulation in large parts of the brain”

[17] (Eldreth et al. 2004) Suggests that Heavy use is off set by accessing different neural pathways.

“Alternatively, it has also been suggested that heavy cannabis users recruit alternative neural

networks as a compensatory mechanism during task performance.”

[18] (Kanayama et al. 2004) This study demonstarted that cannabis users utilized additional

brain regions, which applies to patients.

“compared with controls, cannabis users utilized additional brain regions to perform cognitive

tasks, i.e., they compensated by working harder and recruiting compensatory networks.”

[19] (UK House of Lords Select Committee on Science and Technology. 1998. Ninth Report.

London: United Kingdom. Chapter 4: Section 4.7.) Supports a ability to drive with a extremely

high ng/ml ratio, as levels would be around 150 ng/ml immediately after consumption.

“Intoxication with cannabis leads to a slight impairment of psychomotor … function. …

[However,] the impairment in driving skills does not appear to be severe, even immediately after

taking cannabis, when subjects are tested in a driving simulator. This may be because people

intoxicated by cannabis appear to compensate for their impairment by taking fewer risks and

driving more slowly, whereas alcohol tends to encourage people to take great risks and drive

more aggressively.”

[20] (Source: Kurzthaler I, et al. Hum Psychopharmacol 2005 Apr 18;) This shows patients with

neuropathic illness are not impaired like recreational users.

“The effects of the synthetic cannabinoid nabilone on driving ability was investigated in 6

patients with multiple sclerosis and spasticity. In a crossover design they received either 2 mg

nabilone/day or placebo. No indication was found of a deterioration of any of the five

investigated neuropsychological functions (reaction time, working memory, divided attention,

psychomotor speed and mental flexibility) during the 4-week treatment period with nabilone.

Nabilone shows similar effects as THC, 1 mg of nabilone comparing to about 10 mg THC.”

[21] (Source: Strohbeck-Kuehner P, Skopp G, Mattern R. Fahrtüchtigkeit trotz (wegen) THC.

[Fitness to drive in spite (because) of THC] [Article in German] Arch Kriminol 2007;220(1-2):

11-9.) Demonstrates some patients can not only drive with higher levels but their latent THC

levels must also be high.

“Scientists at the Department for Forensic and Traffic Medicine of the University of Heidelberg,

Germany, investigated the effects of cannabis on driving related functions in a 28 year old man

with attention-deficit/hyperactivity disorder (ADHD). He had violated traffic regulations several

times in recent years and his driving licence was revoked due to driving under the influence of



19

cannabis. He showed abnormal behaviour, seemed to be significantly maladjusted and his

concentration was heavily impaired while sober during the first meeting with a psychologist. He

was allowed to perform driving related tests under the influence of the cannabis compound

dronabinol (THC), which his doctor had prescribed him to treat his symptoms. The examiner

expected that he was not able to drive a car under the acute influence of THC.

But at the second visit his behaviour was markedly improved and he performed average and

partly above-average in all tests on reaction speed, sustained attention, visual orientation,

perception speed and divided attention. A blood sample taken after the tests revealed a high THC

concentration of 71 ng/ml in blood serum. He admitted later to have smoked cannabis and not

taken dronabinol, because it was too expensive. Researchers noted that "people with ADHD are

found to violate traffic regulations, to commit criminal offences and to be involved in traffic

accidents more often than the statistical norm" and conclude from their investigation that "it has

to be taken into account that in persons with ADHD THC may have atypical and even

performance-enhancing effects.”

[22] (Evening News of 24 January 2004) Demonstrates that cannabis can improve driving

performance and would certainly apply to medical use.

“According to research by British scientists a moderate amount of cannabis may actually

improve driving performance. A group of 20 drivers aged 21-40 participated in a driving

simulator test. Ten of them smoked the equivalent of about half a cannabis cigarette. Subjects

under cannabis scored superior than the sober subjects in most of the tasks including reaction

time and number of collisions. Simon Smith Wright, the director of the laboratory where the

studies were conducted, said: "The results of our test clearly show that a small or moderate

amount of cannabis is actually quite beneficial to someone's driving performance."

[23] (Starmer et al., 1988, p. 35-36) Calls rigid ng/ml limits into question and suggests that patients are not effected the same.

"There has developed an understandable but regrettable tendency to separate alcohol from other

impairing agents and at the same time to enact tough drugs-driving legislation which remains

firmly based on experience with alcohol. This is illogical, inappropriate and usually quite

unenforceable. There is often pressure to define, for legal purposes, critical body fluid

concentrations above which all would be impaired and below which no impairment would be

demonstrable. At present, this is not possible. In addition to the considerably more complex

pharmacokinetic and pharmacodynamic effects of most drugs compared with those of ethanol,

there is also the proposition that therapeutic drugs, used for legitimate purposes, may improve

the driving ability of certain patients despite their ability to impair performance normal

individuals."

[24] (UK Department of Environment, Transport and the Regions (Road Safety Division). 2000.

Cannabis and Driving: A Review of the Literature and Commentary. Crowthorne, Berks: TRL

Limited.) Suggests that changes caused by cannabis do not compromise driving like impairment

caused by alcohol.



20

“This report has summarized available research on cannabis and driving. Evidence of

impairment from the consumption of cannabis has been reported by studies using laboratory

tests, driving simulators and on-road observation. ... Both simulation and road trials generally

find that driving behavior shortly after consumption of larger doses of cannabis results in (i) a

more cautious driving style; (ii) increased variability in lane position (and headway); and (iii)

longer decision times. Whereas these results indicate a 'change' from normal conditions, they do

not necessarily reflect 'impairment' in terms of performance effectiveness since few studiesreport increased accident risk .”

[25] (New Scientist of 19 March 2002) These findings make it clear that there is no clear anaogy

between alcohol and cannabis use.

“A single glass of wine impairs driving ability more than smoking a cannabis cigarette. These are

the findings of a major new study by the Transport Research Laboratory in Crowthorne (UK).

They confirm the results of a preliminary study more than a year ago. The study also found that

drivers on cannabis tended to be aware of their intoxicated state, and drove more cautiously to

compensate their impairment.”

[26] (F Grotenhermen et al. Addiction Volume 102 Issue 12 Page 1910-1917, December 2007)

THC combined with BAC impairs, could apply to 5ng/ml limit.

“Finally, a legal per se limit for cannabis must consider that the concurrent use of alcohol and

cannabis impairs driving skills more than each drug individually. For drivers presenting with

measurable THC concentrations and a BAC exceeding 0.03% or 0.05%, a lower per se limit for

THC than proposed above may be appropriate.”

[27] (Grotenhermen et al. 2007) This is in reference to Colorado's DWAI .05% BAC = (5 ng/ml)

and Per Se DUI being .08% BAC = ( 8-11 ng/ml)

“A comparison of meta-analyses of experimental studies on the impairment of driving-relevant

skills by alcohol or cannabis suggests that a THC concentration in the serum of 7–10 ng/ml is

correlated with an impairment comparable to that caused by a blood alcohol concentration

(BAC) of 0.05%.”

[28] Dr. Barry Beyerstein of Simon Frazer University Shows that science does not support a

catch all ng/ml limit for impairment.

"The relationship between THC levels in blood and impairment of eye-hand coordination,

reaction time and other components of driving skill is not a straightforward one. Also, individual

differences of impairment among different users are so great that it would be very difficult to set

a fair legal standard of impairment that would apply to everyone."

DRIVING CITATIONS

[29] (Anderson, B.M., Rizzo, M., Block, R.I., Pearlson G.D. & O’Leary D.S. (2010). Sex



21

Differences in the Effects of Marijuana on Simulated Driving Performance. Journal of

psychoactive drugs, 42(1),19-30.) This study was recent and took modern potency of cannabis

into account dispelling the potency myth.

“In the United States, one in six teenagers has driven under the influence of marijuana. Driving

under the influence of marijuana and alcohol is equally prevalent, despite the fact that marijuana

use is less common than alcohol use. Much of the research examining the effects of marijuana ondriving performance was conducted in the 1970s and led to equivocal findings. During that time,

few studies included women and driving simulators were rudimentary. Further, the potency of

marijuana commonly used recreationally has increased. This study examined sex differences in

the acute effects of marijuana on driving performance using a realistic, validated driving

simulator. Eighty-five subjects (n = 50 males, 35 females) participated in this between-subjects,

double-blind, placebo controlled study. In addition to an uneventful, baseline segment of driving,

participants were challenged with collision avoidance and distracted driving scenarios. Under the

influence of marijuana, participants decreased their speed and failed to show expected practice

effects during a distracted drive. No differences were found during the baseline driving segment

or collision avoidance scenarios. No differences attributable to sex were observed.”

[30] (W. Hindrik and J. Robbe and J. O’Hanlon. 1993. marijuana and actual driving

performance. Washington, DC: US Department of Transportation National Highway Traffic

Safety Administration, Report No. DOT HS 808 078.) Supports cannabis users are aware and can

compensate while driving.

“This report concerns the effects of marijuana smoking on actual driving performance. This

program of research has shown that marijuana, when taken alone, produces a moderate degree of

driving impairment which is related to consumed THC dose. The impairment manifests itself

mainly in the ability to maintain a lateral position on the road, but its magnitude is not

exceptional in comparison with changes produced by many medicinal drugs and alcohol. Driversunder the influence of marijuana retain insight in their performance and will compensate when

they can, for example, by slowing down or increasing effort. As a consequence, THC’s adverse

effects on driving performance appear relatively small.”

[31] (US Department of Transportation, 2003. op. Cit.) Cannabis users are aware of their

impairment and compensate by reducing risk-taking.

“The extensive studies by Robbe and O’Hanlon (1993), revealed that under the influence of

marijuana, drivers are aware of their impairment, and when the experimental task allows it, they

tend to actually decrease speed, avoid passing other cars, and reduce other risk-taking behaviors.”

[32] (Anderson et al. 2010) (Parsons, 2008) Note worthy In light of evidence that text messaging

can be worse than drunk driving.

“ found that being under influence of active cannabis, “did not appear to affect their

[participants’] driving” and observed “many teenagers and young adults driving under the



22

influence of marijuana are doing so while… talking on the cell phone and/or text messaging

others”.

[33] (H. Robbe. 1995. Marijuana’s effects on actual driving performance. In: C. Kloeden and A.

McLean (Eds) Alcohol, Drugs and Traffic Safety T-95. Adelaide: Australia: HHMRC Road

Research Unit, University of Adelaide. Pp. 11-20.) Alcohol's effects on driving cannot be

compared to cannabis.

“Evidence from the present and previous studies strongly suggests that alcohol encourages risky

driving whereas THC encourages greater caution, at least in experiments. Another way THC

seems to differ qualitatively from many other drugs is that the formers users seem better able to

compensate for its adverse effects while driving under the influence.”

[34] (Canadian Senate Special Committee on Illegal Drugs. 2002. Cannabis: Summary Report:

Our Position for a Canadian Public Policy. Ottawa. Chapter 8: Driving Under the Influence of

Cannabis.) What constitutes lower doses is dependant on frequency of use, patients are not

effected by 5 ng/ml doses.

“Cannabis leads to a more cautious style of driving, [but] it has a negative impact on decision

time and trajectory. [However,] this in itself does not mean that drivers under the influence of

cannabis represent a traffic safety risk. … Cannabis alone, particularly in low doses, has little

effect on the skills involved in automobile driving.”

CULPABILIY CITATIONS

[35] (G. Chesher and M. Longo. 2002. Cannabis and alcohol in motor vehicle accidents. In: F.

Grotenhermen and E. Russo (Eds.) (Cannabis and Cannabinoids: Pharmacology, Toxicology, and

Therapeutic Potential. New York: Haworth Press. Pp. 313-323.) There is no solid scientific datathat supports cannabinods alone increase culpability.

“At the present time, the evidence to suggest an involvement of cannabis in road crashes is

scientifically unproven. To date, seven studies using culpability analysis have been reported,

involving a total of 7,934 drivers. Alcohol was detected as the only drug in 1,785 drivers, and

together with cannabis in 390 drivers. Cannabis was detected in 684 drivers, and in 294 of these

it was the only drug detected. The results to date of crash culpability studies have failed to

demonstrate that drivers with cannabinoids in the blood are significantly more likely than drug-

free drivers to be culpable in road crashes. In cases in which THC was the only drug present

were analyzed, the culpability ratio was found to be not significantly different from the no-drug

group.”

[36] (Study of cannabis and driving. Robbe & O'Hanlon, 1993) Cannabis alone does not

seriously impair or increase accident risk.

“The foremost impression one gains from reviewing the literature is that no clear relationship has

ever been demonstrated between marijuana smoking and either seriously impaired driving

performance or the risk of accident involvement. The epidemiological evidence, as limited as it

http://www.druglibrary.org/schaffer/Misc/driving/s1p2.htm

http://www.druglibrary.org/schaffer/Misc/driving/s1p2.htm



23

is, shows that the combination of THC and alcohol is overrepresented in injured and dead

drivers, and moreso in those who actually caused the accidents to occur. Yet there is little if any

evidence to indicate that drivers who have used marijuana alone are any more likely to cause

serious accidents than drug-free drivers.”

[37] (Logan, M.C., Hunter, C.E., Lokan, R.J., White, J.M., & White, M.A. (2000). The

Prevalence of Alcohol, Cannabinoids, Benzodiazepines and Stimulants Amongst Injured Driversand Their Role in Driver Culpability: Part II: The Relationship Between Drug Prevalence and

Drug Concentration, and Driver Culpability. Accident Analysis and Prevention, 32, 623-32.)

Data shows ratio was no higher than the drug free group for cannabinoids alone.

“For each of 2,500 injured drivers presenting to a hospital, a blood sample was collected for later

analysis.There was a clear relationship between alcohol and culpability. In contrast, there was no

significant increase in culpability for cannabinoids alone. While a relatively large number of

injured drivers tested positive for cannabinoids, culpability rates were no higher than those for

the drug free group. This is consistent with other findings.”

[38] (M. Bates and T. Blakely. 1999. “Role of cannabis in motor vehicle crashes.” Epidemiologic

Reviews 21: 222-232.) Supports cannabis alone does not increase culpability.

“Overall, we conclude that the weight of the evidence indicates that: There is no evidence that

consumption of cannabis alone increases the risk of culpability for traffic crash fatalities or

injuries for which hospitalization occurs, and may reduce those risks.”

[39] (Australian Government Report 1996) No epidemiological evidence supports cannabinoids

increase accidents.

"There is no controlled epidemiological evidence that cannabis users are at increased risk of

being involved in motor vehicle or other accidents."

[40] (Weatherburn et al. 2003) Recent study concluding no solid science connecting cannabis to

major road trauma.

“there are no solid grounds for asserting that cannabis intoxication is a major cause of road

trauma”.

[41] (Researchers at the St. Elisabeth Hospital, Tilburg in the Netherlands May 2004) Nederlands

has legal adult cannabis use and would show culpability if increased but still no evidencecannabis causes accidents.

"No increased risk for road trauma was found for drivers exposed to cannabis."

[42] (Source: Movig KL, et al. Accid Anal Prev 2004;36(4):631-6.) This recent study founf

cannabis does not increase risk for accidents like other substances.



24

“Researchers estimated the association between drug use and motor vehicle accidents by

conducting a prospective case-control study from May 2000 to August 2001. The 110 cases were

drivers involved in road crashes, who needed to stay in hospital. The 816 controls were drivers

recruited at random while driving on public roads. The risk for trauma from road accidents was

increased by 5-fold with use of benzodiazepines. The risk for alcohol was increased by 5.5 with a

blood alcohol concentrations (BAC) between 0.05-0.08 per cent and by 15.5 with a BAC above

0.08 per cent. Increased risks were assessed for drivers using amphetamines, cocaine, or opiates. No increased risk was found for drivers who had used cannabis.”

[43] (Source: Laumon B, Gadegbeku B, Martin JL, Biecheler MB. Cannabis intoxication and

fatal road crashes in France: population based case-control study. BMJ 2005 Dec 2)

Grotenhermen's study is one of the most sited studies for the 5 ng/ml limit, yet he states BAC

and age as being the main factors.

“Researchers of the French National Institute for Transport and Safety Research and other

French research institutions presented results of the largest ever conducted study on cannabis and

driving in the British Medical Journal. The government funded study confirms results of earlier investigations that found no or only a small increase in the risk of causing an accident following

the use of cannabis. The risk increased with increased THC blood concentrations as already

observed in an Australian study published in 2004.

In a letter to the British Medical Journal Dr. Franjo Grotenhermen of the German nova-Institut

wrote. "The presentation of the results in the abstract is somewhat misleading. The figures for the

unadjusted odds ratios suggest a more than threefold risk increase for all THC positive drivers

and a more than twofold increase even for drivers with a THC blood concentration of less than 1

ng/ml. However, closer review of the results shows that two other factors contributed to the

higher accident risk, i.e., alcohol consumption and the younger age of the THC positive drivers,

compared to the whole cohort. About 42 per cent of THC positive drivers also tested positive for

alcohol, with a blood alcohol concentration (BAC) of 0.05 percent. Even an BAC below 0.05 per

cent was reported to be associated with an odds ratio of 2.7 in the study, but no data were given

on the percentage of THC positive drivers with an additional BAC < 0.05 per cent. Thus, no

information is available on drivers who had only THC in their blood and on their risk of causing

an accident, which has been used as a standard way of reporting in previous studies."

[44] (Source: Libération of 3 October 2005) This study shows that the cannabis culpability ratio

is lower than BAC .05%.

“Drivers under the influence of cannabis are far less likely to be culpable in traffic accidents thandrunk drivers. According to the newspaper "Libération" the results of an epidemiological study

with approximately 8,000 accidents will be published in several weeks in the British Medical

Journal.

Researchers at the French National Institute for Research on Transportation and Safety found

that alcohol intoxication and speeding were nearly ten times more likely to be an attributing

factor in traffic fatalities than the use of cannabis. Overall, researchers estimated that cannabis'



psychomotor impairment was similar to that exhibited by drivers with blood alcohol

concentrations (BAC) ranging from 0.02 to 0.05 per cent. The relative risk for causing a fatal

accident was 1.8-2.2 for cannabis, similar to that for alcohol below a BAC of 0.05. It was about

20 for alcohol above a BAC of 0.05 and speeding.

The study results have been provoking the greatest embarrassment among government officials

since they always claimed that "drugs behind the wheel are responsible for more deaths thanspeeding." Under French law, drivers who test positive for even trace levels of THC in their

blood face up to two years in prison.”

[45] (Ramaekers et al. 2004. Dose related risk of motor vehicle crashes after cannabis use. Drug

and Alcohol Dependence 73: 109-119.) The combination of acohol and cannabnoids is the main

cause for increase in culpability, where cannabis is involved.

“Experimental studies have shown alcohol and THC combined can produce severe performance

impairment even when given at low doses. The combined effect of alcohol and cannabis on

performance and crash risk appeared additive in nature, i.e. the effects of alcohol and cannabis

combined were always compara ble to the sum of the ef fects of alcohol and THC when given

alone.”

[46] (Robbe, 1994, p. 177) This study concluded that cannabis alone does not merit a campaign

and is the least harmful substance with respect to driving.

"Of the many psychotropic drugs, licit and illicit, that are available and used by people who

subsequently drive, cannabis may well be amongst the least harmful. Campaigns to discourage

the use of cannabis by drivers are certainly warranted. But concentrating a campaign on cannabis

alone may not be in proportion to the safety problem it causes"

[47] (Drummer et al. Addiction Volume 102, Issue 12, pages 1910–1917, December 2007)

[48] Institute of Medicine "Marijuana and Medicine: Assessing the Science Base" 1998.

http://onlinelibrary.wiley.com/doi/10.1111/add.2007.102.issue-12/issuetoc



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