A recent study conducted at the Johns Hopkins School of Medicine found that secondhand cannabis smoke can intoxicate nonsmokers under "extreme conditions," meaning unventilated rooms. It's the first comprehensive study on secondhand pot smoke released since the 1980s, whose findings needed to be updated since the potency of street marijuana has tripled in recent years. It should also let those who don't partake know that jumping into a car with smokers will probably get them high.

The study, published in Drug and Alcohol Dependence, was led by Evan S. Herrmann, Ph.D., a postdoctoral fellow in psychiatry and behavioral sciences at Johns Hopkins. Researchers recruited a relatively small sample of seven smokers and 12 nonsmokers, all between 18 and 45, for the study. Six from each group were placed side by side in a 10-by-13-foot acrylic enclosure for an hour, and the smokers were given 10 joints with high-potency weed to smoke. In one session, the room was ventilated, while in another it wasn't. As you might imagine, the nonsmokers in the unventilated room got pretty high.

"We found positive drug effects in the first few hours, a mild sense of intoxication and mild impairment on measures of cognitive performance," said Ryan Vandrey, Ph.D., a senior author on the study, in the official release. "These were relatively slight effects, but even so, some participants did not pass the equivalent of a workplace drug test."

Nonsmokers had detectable levels of THC in their blood and urine

While none of the nonsmokers in the ventilated room tested positive for THC, all six of those exposed to the smoke in the unventilated room had detectable levels of THC in their blood and urine. They also felt pleasant, tired, and less alert — stoned, you might say.

Marijuana is enjoying a moment of growing acceptance in the US, with business in places like Colorado booming after successful legalization efforts. While cannabis is considered far less harmful than alcohol or tobacco, the Johns Hopkins study helps illustrate how people might be affected if they choose not to smoke but the people around them do. The short answer is: if you don't feel like getting high, open a window.