Cannabis impairs driving even when users are NOT high, report finds

Even when sober, frequent marijuana users are dangerous drivers, report finds

Researchers tested participants in a driving simulator.

Even when sober, some heavy marijuana users are dangerous drivers, a new study suggests.

The bad driving appears to be isolated to those who started using pot before age 16, researchers reported Tuesday in Drug and Alcohol Dependence. The theory is that early marijuana use changes the brain, leaving people more impulsive and more apt to make rash decisions.

In the new study, which tested participants in a driving simulator, researchers from McLean Hospital in Boston found that sober cannabis users who started using the drug in their teens had more accidents, drove at higher speeds and cruised through more red lights compared to people who had never used marijuana.

"This research suggests that early exposure to cannabis may result in difficulties performing complex cognitive tasks," said co-author Staci Gruber, an associate professor of psychiatry and director of Marijuana Investigations for Neuroscientific Discovery at Harvard Medical School and McLean Hospital.

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