People often wonder if they can get high from secondhand smoke (and by “people” we really mean “people about to be drug screened”). They avoid parties, skip concerts, and stay away from their cousin Marlow – the one who walks around with a permanent marijuana cloud like a stoned version of Pig-Pen from Peanuts. But is all this proactivity necessary? The answer: probably not.

According to the National Institute on Drug Abuse, studies show that a very small amount of THC is put back into the air when a smoker exhales. The amount is so miniscule that sitting in a room with a smoker for an hour wouldn’t get you high. Instead, you’d have to inhale the smoke of around sixteen joints before you’d feel an effect. But what does this kind of contact do to a drug test?

The good news is you’re unlikely to fail a drug test because of secondhand smoke. It’s not impossible to fail one, but it’d take a lot of exposure. A lot of exposure.

What Science Says About Secondhand Smoke

A 2010 study found that nonsmokers who stayed in a well-ventilated room for three hours did have trace amounts of THC in their blood and urine. However, the amount wasn’t enough to fail a test.  Other studies suggest that ventilation plays a very large role in all of this.

Per Live Science, people exposed to secondhand smoke can and do feel its effects: they get high, their thinking clouds, and they fail drug screens. But the conditions must be extreme

A study at Johns Hopkins School of Medicine took twenty people between the ages of 18 and 45 and looked closer at this issue. The cannabis status of those involved varied: some were smokers, some weren’t. The researchers obtained blood, saliva, urine, and hair samples to establish cannabis biomarkers. Then they placed the participants in an aluminum smoke chamber.

They gave half of them marijuana cigarettes that contained potent strains and instructed them to smoke at their leisure; the other participants didn’t smoke but sat next to do those who did. The research occurred in two separate sessions.

In one session, the chamber’s ventilation system was turned on; air circulated in and out at the standard rate found in office buildings. In the other session, ventilation was restricted.

Secondhand smokeThe results were as expected: when the room was ventilated, the secondhand exposure didn’t do much; nonsmokers didn’t feel impaired and they didn’t test positive for THC. When the room was unventilated, nonsmokers showed slight impairment, felt high, and had detectable levels of THC for twenty-two hours after exposure.

The lesson learned: yes, it’s possible to get high from secondhand exposure, but it’s not common. Standing next to someone who’s smoking at a party probably won’t do it, no matter how much you try to convince your boss that it could.

Worth mentioning is the fact that drug screens don’t necessarily come back positive in people who are smokers. Most labs use a cutoff for THC of 50 ng/ml (some labs use a more sensitive test that sets the cutoff at 20 ng/ml but this isn’t the norm). In general, this means that social smokers probably won’t test positive if they haven’t smoked for three or four days and chronic smokers probably won’t test positive if they haven’t smoked for a week. In some rare cases, a test will stay positive for up to thirty days since last exposure (this most often only occurs in people who’ve smoked very regularly for a long period of time or chronic smokers who have a high percentage of body fat).

The above relates to direct exposure and attests to the fickleness of THC in the system: it doesn’t stay there long, not even with overt inhaling. If you can beat a drug screen by abstaining from marijuana for a week or so, you shouldn’t have anything to worry about in regards to secondhand exposure; don’t stress over your roommate who smoked a bowl in front of you last month – go and show that drug test who’s in charge.

The Health Effects of Secondhand Cannabis Smoke

The health effects of secondhand smoke from tobacco cigarettes are well established with many public places now entirely smoke-free. Yet, whether or not passive tobacco is truly as dangerous as believed remains controversial: some studies show a link to poor health, some don’t. The effects of secondhand marijuana smoke are less known.

Because marijuana can be beneficial to health – something tobacco can’t claim – one could argue that its secondhand smoke is harmless at worst and helpful at best

Still, there are lots of factors that contribute to this. Someone with asthma, for example, probably won’t benefit from exposure to any kind of smoke. And others don’t want to risk it; there’s a lot we don’t know about cannabis.

Avoiding Secondhand Smoke

In the event you want to avoid exposure to secondhand marijuana – you’re up for your dream job and won’t take any chances or you don’t like pot – it’s not that difficult. Some of the following tips should help:

Know what you’re getting into: If you go to a 311 concert at Red Rocks in Colorado, you’re gonna smell pot (heck, if you go to a John Tesh concert at Red Rocks in Colorado, you’re gonna smell pot). Avoiding functions that are known for cultivating cannabis might seem unfair, but desperate times call for desperate measures (like ordering concerts on Pay-per-view).

Remember that people don’t mean to offend you: People aren’t using weed so that you’ll be exposed to secondhand smoke; they’re using it so they’ll be exposed to the first-hand kind.

Leave if needed: If you find yourself in a place where there’s a lot of pot smoking – a party for instance – simply leave…or find the homeowner and ask about the intricacies of their ventilation system.

Of course, all of the issues surrounding secondhand marijuana smoke are easily solved in one word: edibles.

Jenn Keeler

About the author: Jenn Keeler is a freelance writer and illustrator specializing in humorous lifestyle articles. She is one of the few people on earth actually using an English degree. Her heart belongs to the Denver Broncos and her husband. In that order.