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Drivers Testing Positive in Urine No More Dangerous Than 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 [01] at the University of Maryland School of Medicine (2005). The study examined 2,405
drivers hospitalized in automobile accidents from 1997 through 2001.
The
study investigated the circumstances of each accident to assess which drivers were at fault or culpable. Drivers testing
positive for marijuana 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,
marijuana-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 marijuana-using
drivers tend to slow down.
This
flatly refutes the rationale for random testing of truck and bus drivers, observed California NORML coordinator
Dale Gieringer, Urine tests for marijuana don't reflect driving impairment. Two
other studies [2] have failed to find higher accident rates for drivers testing positive for marijuana in urine.
An essential reason for these negative results is the reliance on urine tests to detect
marijuana. Urine tests are poor indicators of impairment because they detect non-psychoactive
metabolites that stay in the system for days after marijuana 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 testing positive for THC in
blood.
In
another new accident study [3] - the largest
yet - French researchers examined 10,748 drivers involved in fatal 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 3 at the highest levels (above 5 nanograms THC per milliliter of blood).
In contrast, for alcohol the risk ranged from 3 at the lowest levels (below .05% blood alcohol) to over 40 at the
highest levels. The study has 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 before the study was
complete. The study showed that driving with THC in blood was in fact no riskier than driving at
blood alcohol levels below .05%, which is legally permitted in France. The U.S. allows alcohol
levels up to .08%.
Numerous other studies have found that marijuana is a significantly lesser driving hazard than alcohol. Current
scientific evidence shows clearly that a zero tolerance standard for THC in blood is unjustified, argues California
NORML coordinator Dale Gieringer. An expert panel
report chaired by Dr. Franjo Grotenhermen [4] of the International Association for Cannabis Medicine concluded that
levels above 3.5 to 5 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 can
be consistent with safe driving.
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.
(3)
Bernard Laumon et al, Cannabis Intoxication and fatal road crashes in France: population based case-control study, British
Medical Journal doi:10.1136/bmj.38648.617986.1F, Dec. 2, 2005.
(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 at www.canorml.org/healthfacts/DUICreport.2005.pdf
