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Marijuana and driving ability
After alcohol, Cannabis
is the drug which is found most often in the blood of drivers involved in road accidents.
The effects of THC, the major psychoactive component of Cannabis, on
driving ability have been investigated by Dr. H.W.J. Robbe at the Institute of Human
Psychopharmacology of the University of Limburg in Maastricht, The Netherlands.
In his PhD thesis, "Influence of
Marijuana on Driving" (available through the IHA), which Robbe defended on
May 26, he concludes that marijuana is not a safe drug in traffic. After using
marijuana drivers were less able to drive in a straight line. However, compared to
the effects of alcohol and many medicines (antidepressants and sedatives) on driving
ability, the effects of marijuana are not exceptional.
The use of a moderate amount of marijuana did
not affect driving ability, but the drivers thought their ability had been negatively
affected. The use of a moderate amount of alcohol had a negative effect on driving
ability, while the drivers thought their performance had not been affected. The use
of alcohol seems to stimulate risky behaviour, whereas the use of marijuana leads to a
more prudent driving style.