ABSTRACT
Marijuana is the most widely used illicit drug in the United States with 72 million people reporting having used marijuana in their life. Among individuals who reported driving after drug use, 70% indicated they had smoked marijuana within 2 h of driving. Laboratory studies in which subjects smoked marijuana under controlled conditons have documented that marijuana reliably impaired sensory-perceptual abilities, gross motor coordination, psychomotor abilities, divided and sustained attention, and cognitive functioning, including learning and memory. Other laboratory research has focused on the applied question of whether marijuana impairs driving abilities as measured by standardized field sobriety tests used by police to detect impaired drivers. This research has shown that marijuana impaired balance and psychomotor coordination in a dose-dependent manner. Such behavioral impairment may underlie marijuana-induced decrements in tests of on-road driving. Plasma ∆9-tetrahydrocannabinol (∆9-THC) concentration in the range of 15-30 ng/ml was associated with impaired balance and motor coordination, suggesting that driving abilities would be impaired at the same ∆9-THC concentration. Future research should continue to explore the relationship between plasma ∆9-THC concentration and human performance, and more studies are needed on the effects of marijuana combined with other commonly used drugs, such as alcohol, on driving abilities.
