Half a year since cannabis legalization, it’s become commonplace to walk the streets and smell the evidence of marijuana being smoked. One might ask if we’re in store for more contact highs among non-smokers.
It turns out, a contact high, or second-hand high, may be less of a concern than people expect. Non-smoking bystanders likely have little to worry about—depending on the circumstances.
Dr. Cornel Stanciu, an assistant professor of psychiatry at Geisel School of Medicine at Dartmouth in Lebanon, N.H., says there are two definitions of a contact high—one, where a bystander becomes intoxicated from inhaling second-hand smoke, and two, when a person tests positive for detectable levels of cannabinoids without smoking, due to exposure.
How do you get a contact high?
Auburn Larose, an epidemiologist with the North Bay Parry Sound District Health Unit, says “factors such as the amount of smoke, ventilation and the physical location will impact the extent of second-hand smoke exposure.”
Research backs this up, including the oft-cited 2015 John Hopkins University study, which put non-smokers into rooms with a group of people smoking.
The study found that when the room was ventilated with fans, non-smokers felt no psychoactive effects and did not test positive for THC.
Under extreme, unventilated conditions, the non-smokers were more tired, more “pleasant” and tested positive for tests with cut-off levels at 20 to 50 nanograms (ng) per ml of blood.
Federal law in Canada, for comparison, has prohibited drug concentrations for drug-impaired driving at over two, but under five, ng per ml of blood. This represents a straight summary conviction offence.
Stanciu explains that in addition to ventilation, the level of a contact high also depends on whether smokers are inhaling properly, how potent the cannabis is and, of course, how long it takes the non-smoker’s body to metabolize THC before testing.
A study in the British Journal of Anaesthesia, published in 1999, found that when smoking a cannabis cigarette, about half of the THC and other cannabinoids enter the mainstream smoke and are inhaled. More experienced smokers tend to inhale deeply and absorb almost all the cannabinoids present. Consequently, inexperienced smokers exhale more THC and, therefore, increase the likelihood of a contact high. The potency of cannabis is also changing with newer cultivation practices, and THC levels are higher now overall.
How strong is a contact high?
The Johns Hopkins study found that those in the room without ventilation did experience impairment—the study defines this as whether people were able to complete tasks, but there was also a certain level of THC—via second-hand smoke. Larose, however, says contact high “has not been thoroughly researched. As a result, the impacts of second-hand exposure to cannabis are not well-known,” she adds.
Stanciu is more direct. “If you were to ask me [whether a contact high could be as strong as a consumption high] a few years ago, I would have immediately said no, that is not an option. But in recent years, there have been certain changes that took place, one of them being that the potency of marijuana” is now higher than in years past. “My answer [now] is always, ‘It is very unlikely, but there is still a possibility,’” he adds.
To be clear, Stanciu notes that unlike with alcohol, it is still difficult to tell the difference between whether people are experiencing actual impairment when they test positive for detectable levels of THC. “The content of THC you have in your system doesn’t correlate with whether you are intoxicated or not. There is no way to be able to test for intoxication based on your saliva or blood level of marijuana,” he says. Psychomotor tests can help, but there is still a lack of research on whether regular users are less subject to receiving a contact high, he explains.
So far, studies exploring contact high have focused on smoking cannabis. With legalization of more extraction products on its way, concerns may be raised about the possibility of contact highs through newer usage methods, such as topical exposure. Here, Stanciu agrees with Larose that there isn’t enough research. (He does, however, maintain that it would be “highly unlikely” to get high from the smell of baking an edible without combustion of the cannabis).
For now, whether or not experts can agree that sufficient research exists regarding contact highs, “I certainly think it gives some perspective to legislatures and whoever is in charge of setting the rules and regulations for where [cannabis] can be consumed,” Stanciu adds.
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