POT SMOKING CAN IMPAIR DRIVING ABILITY

NEW YORK, Jul 08 (Reuters Health) -- Driving and marijuana use could be a
dangerous combination, according to European researchers.

"Perceptual motor speed and accuracy, two very important parameters of
driving ability, seem to be impaired immediately after cannabis
consumption,'' conclude Dr. Ilse Kurtzhaler and colleagues at Innsbruck
University Clinics, in Innsbruck, Austria. Their findings were published in
the June issue of the Journal of Clinical Psychiatry. While the detrimental
effects of alcohol on driving ability are well known, "definitive answers''
regarding driving and marijuana use have remained elusive, according to the
authors.

To help resolve this issue, they performed a series of physical and
psychological tests on 60 healthy volunteers who were asked to smoke
regular cigarettes or cigarettes containing tetrahydrocannabinol (THC), the
active agent in marijuana.

The investigators found that, compared with subjects who smoked regular
cigarettes, "the THC group exhibited a significantly higher impairment of
cognitive (intellectual) function'' after smoking the drug.

Specifically, the THC group saw their intellectual function decline in two
main areas -- 'perceptual motor speed' and 'accuracy.' Impairment in
perceptual motor speed means that a driver misjudges speed, for example,
thinking he is driving 50 miles per hour when in fact his speed is much
faster. Driving accuracy refers to the driver's ability to respond quickly
and effectively to new, potentially dangerous driving events.

THC smokers also had trouble remembering experiences from psychological
tests run the previous day, according to the researchers. This suggests
that "a driver under acute cannabis influence would not be able to use
acquired knowledge from earlier experiences adequately to ensure road
safety,'' they explain.

Based on these findings, Kurzthaler's team speculate that roadside tests
aimed at detecting marijuana use could become standard practice in the
not-too-distant future.

In an interview with Reuters Health, Dr. Jag Khalsa of the National
Institute of Drug Abuse in Bethesda, Maryland, called the Austrian research
one of the first "well-controlled'' studies on the issue, conducted in a
"scientific manner.''

Still, he believes that more research is needed before US legislators,
health authorities and law-enforcement officials make any move towards
mandating THC checks for American drivers. In any case, he said, "I don't
think we have a sound (testing) technology yet.''

SOURCE - Journal of Clinical Psychiatry 1999;60:395-399.