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Can You Get High On Secondhand Cannabis Smoke?

In many ways, life would be much easier if you could get stoned from secondhand cannabis smoke. For starters, it would make things much cheaper and allow multiple people to get high off one stoner’s exhalations.

Alas, the chances of getting baked after breathing in secondhand marijuana smoke are, unfortunately, pretty slim. Or, fortunately, if you were worried about it.

What Happens When You Breathe In Secondhand Cannabis Smoke?

Most of the buzz around passive smoking actually surrounds secondhand cigarette smoke, which has been linked to several health effects, including disruption to blood vessels and vascular endothelial function.

However, while many studies exist on the health risks of exhaled tobacco smoke, there’s not much information about whether or not indirect weed smoking gets you high.

secondhand cannabis smoke

Despite this, many people claim that a secondhand high – otherwise known as a contact high – can be experienced by hotboxing a small space. While there may be an element of truth to this claim, the reality is you probably need to breathe in a massive quantity of secondhand weed smoke to feel any kind of buzz.

  • One study from 2019 examined the effects of secondhand smoke exposure among police officers at a 53,000-seater stadium in a U.S. state where weed has been fully legalized. Analysis of the air within the venue indicated that tetrahydrocannabinol (THC) was present in the personal breathing space of every single officer, yet none reported any psychoactive effects[i].

Having said that, a minority of officers claimed to have experienced a few other side effects commonly associated with smoking weed, such as red eyes and a dry mouth. About a third of those taking part in the study also had detectable levels of THC in their urine, although none of these was at the concentration required to fail a drug test.

Of course, this study occurred in a large, open-air venue, which is obviously very different from hanging out in a smoky, unventilated room. It’s logical to assume that sitting in an enclosed space with a bunch of stoners would allow for non-smoker exposure to a higher amount of THC, possibly resulting in a contact high. However, you’re very unlikely to experience anything close to a full stone from secondhand weed smoke alone.

Can You Fail A Drug Test From Secondhand Smoke Exposure?

While some people may be keen to save a few bucks by getting high off their pals’ blowouts, others are desperate to avoid the effects of secondhand smoke lest they fail a drug test. However, there’s probably little cause for concern once again as the chances of inhaling enough cannabinoids to fail a test are virtually zero.

When cannabis smoke enters the lungs, it diffuses into the blood and eventually finds its way to the liver. Here, enzymes convert THC into a soluble metabolite called THC-COOH, which is then excreted in urine and other waste products. It’s this metabolite that drug testers look for when they want to bust someone for marijuana use, and while most analyses only look at a person’s pee, some may also take blood, saliva or hair samples.

In 2005, researchers hotboxed an eight-seater van to examine the effects of “severe passive smoke exposure”. For the study, four non-smokers sat next to four marijuana smokers, who each blazed a joint containing either 5.4 per cent or 10.4 per cent THC. Drug test results indicated that small quantities of the cannabinoid were present in the oral fluid of non-smokers but that levels returned to zero after less than 45 minutes[ii].

secondhand cannabis smoke

The experiment was then repeated, yet this time saliva samples were taken after passengers exited the van rather than while they were still in the hotbox. Amazingly, no THC was found in any of the samples, suggesting that the first round of results were probably false positives caused by contamination with weed smoke inside the van.

“Oral fluid specimens collected in the presence of cannabis smoke appear to have been contaminated, thereby falsely elevating THC concentrations in oral fluid,” explained the study authors. “The risk of a positive test for THC was virtually eliminated when specimens were collected in the absence of THC smoke,” they continued.

Overall, these results suggest that the only way to get busted for passively smoking weed would be if someone came and collected your saliva while you’re still surrounded by smoke. Obviously, this isn’t something that’s particularly likely to happen unless you’re ridiculously unlucky.

Another study, conducted in 2015, investigated the effects of passive exposure to cannabis smoke in a sealed chamber and a ventilated room. Urine test results showed that some hotboxed participants had enough THC in their sample to fail, but these levels dropped off after just a few hours. In contrast, none of the participants in the ventilated chamber had detectable levels of cannabinoids in their pee[iii]

Based on this finding, the researchers conclude that “positive tests are likely to be rare, limited to the hours immediately post-exposure, and occur only under environmental circumstances where exposure is obvious.” In other words, it’s almost impossible to unknowingly inhale enough secondhand marijuana smoke to get busted.

How Much Secondhand Weed Smoke Are You Likely To Inhale In Real Life?

While both of the aforementioned studies attempted to investigate the effects of marijuana when inhaled in a highly contrived environment, another looked at the consequences of secondhand cannabis smoke in a real-life situation. Eight participants spent three hours in a popular coffee shop in the Netherlands, where they were surrounded by regular customers and a fair amount of weed smoke.

secondhand cannabis smoke

Blood samples were taken at various time points, and while trace amounts of THC were detectable after 1.5 hours and three hours, no cannabinoids were present at the six-hour follow-up. Importantly, none of the participants had sufficient THC in their urine to fail a drug test at any point during the study[iv].

Furthermore, no one involved in this research reported any impairment, indicating that sitting around in a Dutch coffee shop all day won’t get you high – unless you actually buy a joint, of course.

[i] NIOSH [2019]. Evaluation of police officers’ exposure to secondhand cannabis smoke at open-air stadium events. By Wiegand DM, Methner MM, Grimes GR. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Health Hazard Evaluation Report 2017-0174-3335,

[ii] Niedbala RS, Kardos KW, Fritch DF, Kunsman KP, Blum KA, Newland GA, Waga J, Kurtz L, Bronsgeest M, Cone EJ. Passive cannabis smoke exposure and oral fluid testing. II. Two studies of extreme cannabis smoke exposure in a motor vehicle. Journal of Analytical Toxicology. 2005 Oct 1;29(7):607-15. –

[iii] Cone EJ, Bigelow GE, Herrmann ES, Mitchell JM, LoDico C, Flegel R, Vandrey R. Non-smoker exposure to secondhand cannabis smoke. I. Urine screening and confirmation results. J Anal Toxicol. 2015 Jan-Feb;39(1):1-12. –

[iv] Röhrich J, Schimmel I, Zörntlein S, Becker J, Drobnik S, Kaufmann T, Kuntz V, Urban R. Concentrations of delta9-tetrahydrocannabinol and 11-nor-9-carboxytetrahydrocannabinol in blood and urine after passive exposure to Cannabis smoke in a coffee shop. J Anal Toxicol. 2010 May;34(4):196-203. –

Cultivation information, and media is given for those of our clients who live in countries where cannabis cultivation is decriminalised or legal, or to those that operate within a licensed model. We encourage all readers to be aware of their local laws and to ensure they do not break them.

Ben Taub