The Grapevine

Scientists Test Secondhand Smoke Effects Of Marijuana, Find 'Contact High' Is Real

contact high
Smoking marijuana in an unventilated room can produce milder versions of the same physiologic effect in nearby non-smokers. Rafael Castillo, CC BY 2.0

Smoking marijuana in an unventilated room — “hotboxing,” to the uninitiated — is a surefire way to increase a person’s physiological effects to the drug, a new study finds, thus confirming empirically what anecdotal evidence has taught pot smokers for decades.

As Americans’ attitudes toward cannabis swing from blind disgust to tentative acceptance, research into the drug’s unique, blanketing effects has started to become more robust. It doesn’t just get you high, the studies find. Rather, it can offer relief for inflammatory diseases, soothe chronic pain, and jumpstart the appetites of people who suffer from eating disorders. But while the plant has much of academia on its side, its reputation has had a harder time catching up.

Which is probably why Evan Herrmann and the rest of the study’s co-authors don’t actually use words like “hotboxing” and “pot.” Instead, they describe a test involving six individuals exposed to secondhand cannabis smoke inside a Plexiglas room, whose ventilation levels they could control manually. They were looking at how much the non-smokers were affected by the lingering smoke.

At the end of the experiments, after smokers had either filled the sealed room with smoke or allowed the smoke to leave through vents, the researchers found ventilation ultimately made a large difference in the non-smokers’ physiology. Their heart rates picked up, their cognitive skills waned, and they got a little hungrier. (This last effect is partially suspect, Herrmann admits, since the trial ended near lunchtime.) In the ventilated condition, however, subjects’ blood tests showed far lower cannabinoid levels and their cognitive skills fell mostly at baseline.

To Herrmann, the results suggest a possible, though perhaps implausible, scenario in which secondhand smoke could sabotage new employees hoping to espouse a clean record or the average citizen mixed up in a possession charge. “It would be pretty unlikely for someone to fail a drug test from most ‘real-world’ secondhand exposure scenarios where the environment is ventilated,” Herrmann told Medical Daily in an email.

However, as the study showed, unventilated conditions put one participant above the THC threshold of 50 nanograms per milliliter for urine tests, a standard concentration used by most government positions. Four of the five remaining subjects surpassed the 20 ng/mL threshold used by some private companies, the authors explain.

Marijuana is currently the most widely used illicit drug, and a solid amount of evidence exists to suggest it’s becoming more potent with time. Fortunately, that trend won’t likely result in greater rates of failed drug tests, given that dispensaries trade mostly in edibles and other oral routes of ingestion. In addition, many of their clientele are simply seeking the drug’s medicinal benefits, not its psychoactive properties. In these cases, THC isn’t a factor.

Herrmann says the research is following the trend. “We've moved on from the passive smoke exposure,” he said. “We're now studying the effects of oral cannabis — specifically looking at how different doses of orally consumed cannabis effect behavior/cognition and drug testing results.”

Source: Herrmann E, Cone E, Mitchell J, et al. Non-smoker exposure to secondhand cannabis smoke II: Effect of room ventilation on the physiological, subjective, and behavioral/cognitive effects. Drug and Alcohol Dependence. 2015.

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