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