Medically Reviewed by
Jason Crawford

Article Last Updated on December 24, 2022

Marijuana use has become quite common in the US, mainly as a result of the increased legalization laws on a state level. And as cannabis use has increased, so has workplace drug testing. Ever since the Regan administration first required federal employees to undergo mandatory drug testing, this has become common in a lot of companies in the US and around the world. 

While users who consume cannabis on a regular basis will without a doubt get a positive result if they don’t detox before the drug test, do non-users who have been exposed to secondhand cannabis smoke have a chance of having detectable levels of delta-9-tetrahydrocannabinol (THC) or its metabolites in the body? Read on to find out.

The Effects of Secondhand Cannabis Smoking

Marijuana smokers are usually either in search of the psychoactive effects that THC provides, or the sedative and anti-inflammatory effects which come from the cannabinoid CBD. However, there are often people in the group who don’t enjoy consuming marijuana but inhale secondhand smoke regardless. So, you may be asking yourself how secondhand smoke affects these “passive users.”

You probably know that exhaling cannabis smoke results in increased levels of CO2 in a room, which may cause slight oxygen deprivation for the people who are inhaling the secondhand smoke. Similar to tobacco smoke, marijuana smoke contains harmful toxins and potential carcinogens which are inhaled even through secondhand smoke. Due to smoke exposure being especially harmful to children, it would be best not to smoke marijuana in closed rooms when children are present.

Getting “Contact High” From Secondhand Marijuana Smoke

One of the most common misconceptions when it comes to secondhand cannabis smoke is getting “contact high” from being in the same room as people who smoke cannabis. To figure this out, scientists have done multiple studies.

A 2010 study focussed on researching whether people who stayed at a coffee shop in Amsterdam for 3 hours where people were smoking and vaping cannabis would get a positive urine drug test. The results of the study showed that the nonsmokers had slight increases in their THC levels, but not enough to get high or get a positive test result.

A study by the Johns Hopkins University School of Medicine also researched secondhand smoke exposure in nonusers who were sitting in a closed room where 6 out of 12 people were smoking high-potency cannabis. The first test was done with the fans turned on, and the second without the fans. Even though the nonsmokers had side effects from the smoke they inhaled, the cannabis high wasn’t one of them.

A report from National Institute on Drug Abuse (NIDA) also concluded that it’s highly unlikely for someone to get “contact high” by inhaling secondhand marijuana smoke. Throughout the research, they looked at factors including hours of exposure, the concentrations of THC in the cannabis, as well as the ventilation in the room. People staying in unventilated rooms where there is a high concentration of cannabis smoke may experience impaired function of their blood vessels, as well as other cognitive and performance impairments.

Will You Have a THC-Positive Drug Test From Secondhand Marijuana Smoke?

The studies mentioned in the paragraph above included drug tests such as oral fluid testing, blood, urine, and hair testing to figure out whether nonsmokers would have increased amounts of THC in their bodies and whether they were over the federal cutoff limits for cannabis.

Out of all the tests which were done, the only positive test was the urine test, although the person was tested immediately after cannabis exposure. Herrmann, one of the researchers who performed the study, concluded that it’s only possible to get a positive drug test result from passive smoke inhalation under extreme conditions. The positive results were noted in cases where people were exposed to secondhand cannabis smoke in unventilated rooms for a longer period of time, and the drug testing was done immediately after exposure, or after a 30-minute window of exposure.

Before taking a cannabis test at work, avoid being in unventilated rooms where you’d inhale passive smoke to minimize all risks of getting a positive result.

Secondhand Cannabis Smoke and Other Health Risks

Passive smoke exposure won’t get you high, but you can still experience other health risks if you stay in an unventilated room where weed is smoked. The research is limited since scientists are mostly focusing on researching how direct consumption of cannabis affects users, but it isn’t non-existing.

According to research, secondhand exposure to cannabis smoke while sitting in an unventilated room may result in the following-short term effects:

In the long run, secondhand cannabis exposure may also affect the function of the blood vessels and the effects of the exposure may even last longer than secondhand tobacco smoke. (Xiaoyin Wang et al, 2016)

Moreover, long-term secondhand cannabis exposure may affect lung health by irritating the lungs and throat since cannabis smoke contains harmful chemicals and tar same as tobacco smoke. Some researchers are even focusing on finding out whether long-term exposure to cannabis smoke increases the chances of developing lung disease or lung cancer. (Donald P Tashkin et al, 2013)

To ensure that nonsmokers don’t experience these potential side effects, it’s best to regularly ventilate the room where marijuana is smoked, especially if you’re smoking weed multiple times a day.

Final Thoughts on Testing Positive for THC From Secondhand Marijuana Smoke

Even though marijuana is widely used as both a recreational and a medicinal drug, exposure to secondhand cannabis smoke may result in unwanted effects. From coughing to experiencing slight cognitive and performance impairment, and even increased heart rate, passive exposure to marijuana smoke leaves a lot of people fearful.

While cannabis smoke may lead to the above-mentioned side effects, one thing it can’t produce is a psychoactive high and a positive drug test. Therefore, nonsmokers shouldn’t fear testing positive at their mandatory drug test at work, because that’s highly unlikely.

However, if you’d like to prevent even the most minimal side effects of passive cannabis smoke exposure, make sure you stay in a ventilated room or somewhere close to the windows if there are cannabis smokers present in the room.

Additional Sources

Wang, X., Derakhshandeh, R., Liu, J., Narayan, S., Nabavizadeh, P., Le, S., Danforth, O. M., Pinnamaneni, K., Rodriguez, H. J., Luu, E., Sievers, R. E., Schick, S. F., Glantz, S. A., & Springer, M. L. (2016). One Minute of Marijuana Secondhand Smoke Exposure Substantially Impairs Vascular Endothelial Function. Journal of the American Heart Association, 5(8), e003858. https://doi.org/10.1161/JAHA.116.003858

Tashkin D. P. (2013). Effects of marijuana smoking on the lung. Annals of the American Thoracic Society, 10(3), 239–247. https://doi.org/10.1513/AnnalsATS.201212-127FR

A passionate advocate for the benefits of cannabis. Fraser Horton, who has a background in botany and a strong love of nature, has spent years researching how cannabis affects the body and mind. He established Leaf Nation in 2020, where he has devoted himself to educating people about the legalisation of marijuana and its safe and responsible use. Fraser is committed to highlighting cannabis’ potential for improving wellness and working to dispel the stigma associated with its use.


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