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New accident studies confirm cannabis is less a driving hazard than alcohol |
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Written by Dale Gieringer, Ph.D
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Wednesday, 08 February 2006 |
Studies find drivers with cannabinoids in urine as safe as drug-free drivers
Drivers who test positive for marijuana in urine are no more likely to
cause accidents than drug-free drivers, according to a study led by Dr.
Carl Soderstrom[ 1 ] at the University of Maryland School of Medicine
(2005). The study examined 2,405 drivers hospitalized in automobile
accidents from 1997 through 2001.
Statistically, cannabis-using drivers aged 41 to 60 were less likely
to be at fault for accidents than drug-free drivers, perhaps because
they tend to slow down.
The study investigated the circumstances of each
accident to assess which drivers were at fault or culpable. Drivers
testing positive for cannabis were found to have no greater culpability
than drug-free drivers. In every age group, alcohol was the drug most
strongly associated with crash culpability. Cocaine users also showed
higher crash culpability, especially in the age range of 21-40.
Significantly, cannabis-using drivers aged 41 to 60
were statistically less likely to be at fault for accidents than
drug-free drivers. Similar results have been suggested in other
studies, perhaps because cannabis-using drivers tend to slow down.
This evidence flatly refutes the rationale for
random testing of truck and bus drivers, say critics of the
government’s far-reaching and invasive drug testing program. Two other
studies[ 2 ] have also failed to find higher accident rates for drivers
testing positive for cannabis in urine.
An essential reason for these negative results is
the reliance on urine tests to detect cannabis. Urine tests are poor
indicators of impairment because they detect non-psychoactive
metabolites that stay in the system for days after cannabis is smoked.
Blood tests, which measure the presence of psychoactive THC, provide a
better indication of current impairment. Usually they register positive
for only a few hours after smoking, though low levels of blood THC may
persist in heavy users for a day or two. Some — though not all —
studies have found higher accident rates for drivers with THC in blood.
French officials embarrassed
In the most recent accident study[ 3 ] — the largest
yet — French researchers examined 10,748 drivers involved in fatal
automobile crashes for traces of drugs and alcohol in blood.
The study found that the presence of THC in blood
was associated with a somewhat higher risk of responsibility for
accidents, but significantly less so than alcohol. The increased risk
for THC was dose-dependent, ranging from 1.6 at trace levels to three
at the highest levels (above five nanograms THC per milliliter of
blood).
In contrast, for alcohol the risk ranged from 3 at
the low end (below 0.05% blood alcohol) to over 40 at the highest
levels.
The study proved embarrassing for drug warriors in
the French government, who had prematurely rushed to pass a “zero
tolerance” DUI law barring any blood traces of THC. The study showed
that driving with THC in blood was in fact no riskier than driving at
blood alcohol levels below 0.05%, which is legally permitted in France.
The U.S. allows alcohol levels up to 0.08%.
Numerous other studies have found that cannabis is a
significantly lesser driving hazard than alcohol. Current scientific
evidence shows clearly that a zero tolerance standard for THC in blood
is unjustified, according to most experts.
An expert panel report chaired by Dr. Franjo
Grotenhermen[ 4 ] of the International Association for Cannabis
Medicine concluded that levels above 3.5 to five nanograms per
milliliter of THC in blood are generally indicative of impairment. On
the other hand, there is considerable evidence indicating that lower
levels of blood THC are compatible with safe driving.
Data favors on-site consumption
Despite overwhelming evidence that cannabis is safer
than alcohol, local public officials have been skeptical. Oakland City
Council members voiced concern about driving safety in voting to ban
on-site consumption in cannabis dispensaries. Cannabis advocates
replied that on-site smoking would be a negligible concern in a city
with 802 licensed alcohol outlets. In Alameda County, advocates
prevailed upon the Supervisors to allow on-site consumption with
vaporizers, but only with prior approval by the Health Department.
A California NORML poll found that 75% of San
Francisco voters approved of on-site smoking at medical cannabis
dispensaries. The Board of Supervisors voted to allow on-site smoking
in the city’s dispensary ordinance. Advocates are lobbying for a
similar policy in Oakland.
* Gieringer is director of California NORML. Adapted
from CANorml December 2005 reports,
www.canorml.org/healthfacts/drivingstudy_new.htm
REFERENCES
(1) Carl Soderstrom et al, “Crash Culpability Relative to Age and Sex
for Injured Drivers Using Alcohol, Marijuana or Cocaine,” 49th Annual
Proceedings of the Association for the Advancement of Automotive
Medicine, Sept. 13-14, 2005.
(2) Lowenstein and Koziol-McLain “Drugs and traffic crash
responsibility: a study of injured motorists in Colorado,” J Trauma
50(2):313-30 (2001); and KLL Movig et al, “Psychoactive substance use
and the risk of motor vehicle accidents” [in the Netherlands], Accident
Analysis and Prevention 36: 631-6 (2004).
(3) Bernard Laumon et al, “Cannabis Intoxication and fatal road crashes
in France: population based case-control study,” British Medical
Journal, Dec. 2, 2005. doi:10.1136/bmj.38648.617986.1F
(4) Franjo Grotenhermen et al., “Developing Science-Based Per Se Limits
for Driving under the Influence of Cannabis: Findings and
Recommendations by an Expert Panel,” (International Association for
Cannabis Medicine, 2005) posted online at
www.canorml.org/healthfacts/DUICreport.2005.pdf.
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Dale Gieringer, Ph.D |
| About the author: |
|  Dr. Dale Gieringer received his Ph.D. at Stanford on the topic of DEA drug regulation. He is the author of articles on marijuana and driving safety, drug testing, marijuana health mythology, the economics of marijuana legalization, and DEA "drug enforcement abuse." He is presently working on a book on medical use of marijuana. He has also sponsored research on the use of water pipes and vaporizers to reduce harmful tars in marijuana smoke. |
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Last Updated ( Thursday, 03 August 2006 )
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