'Extreme' exposure to secondhand cannabis smoke causes mild intoxication

Secondhand exposure to cannabis smoke under "extreme conditions," such as an unventilated room or enclosed vehicle, can cause nonsmokers to feel the effects of the drug, have minor problems with memory and coordination, and in some cases test positive for the drug in a urinalysis. Those are the findings of a Johns Hopkins University School of Medicine study, reported online this month in the journal Drug and Alcohol Dependence.

Cannabis is the most widely used illicit drug in the world. "Many people are exposed to secondhand cannabis smoke," says lead author Evan S. Herrmann, Ph.D., a postdoctoral fellow in psychiatry and behavioral sciences at Johns Hopkins. "The scenario we looked at was almost a worst-case scenario. It could happen in the real world, but it couldn't happen to someone without him or her being aware of it."

"We found positive drug effects in the first few hours, a mild sense of intoxication and mild impairment on measures of cognitive performance," says senior author Ryan Vandrey, Ph.D. , an associate professor of psychiatry and behavioral sciences at Johns Hopkins. "These were relatively slight effects, but even so, some participants did not pass the equivalent of a workplace drug test."

The new research is the most comprehensive study of secondhand cannabis smoke and its effects since the 1980s, when researchers found the drug's active ingredient, tetrahydrocannabinol, or THC, and other cannabis byproducts could turn up in nonsmokers' bodies after an hour or more spent in extreme conditions with heavy smokers in an enclosed space.

That finding needed updating, since the average potency of street cannabis has tripled since the 1980s, the Johns Hopkins researchers wrote. Additionally, many earlier studies did not look at whether the nonsmokers reported feeling the drug's effects, or whether their behavior and thinking were affected by secondhand smoke, as the new study did.

Researchers recruited seven people ages 18 to 45 who said they smoked cannabis at least twice per week and tested positive for THC, but who tested negative for other drugs, and 12 others in the same age range who said they had not used cannabis in the past six months and tested negative for cannabis, other drugs, and alcohol. None of the participants were pregnant, and none of the nonsmokers took part in more than one session.

Six smokers and six nonsmokers spent an hour sitting side by side in a 10-by-13-foot, acrylic-walled room in two different experimental sessions. Each smoker was given 10 high-potency cannabis cigarettes to smoke. In one session, the room's ventilation fans were turned on. In another session, the fans were turned off, and the room became smoke-filled. This was a realistic simulation of home ventilation conditions. At the end of the exposures, smokers' and nonsmokers' blood, urine, saliva and hair were tested at regular intervals for THC.