Medically Reviewed by
Jason Crawford

Article Last Updated on January 11, 2023

Legalization laws are changing each year, especially in the US where 18 states have already legalized marijuana. This has brought on more research into cannabis and how it affects smokers, including passive smokers.

People who don’t smoke weed but are often in the presence of people who use cannabis fear they’ll test positive on their next mandatory workplace drug test. They assume that being exposed to the smoke by smelling weed will result in an unpleasant conversation with their manager at work. But is that true? Will smelling weed result in a positive drug screen?

This will be the focus of today’s article. We’ll cover how marijuana use affects nonsmokers in a room filled with cannabis smoke and whether they’ll get positive drug test results on their next drug screen as well as how second-hand weed exposure affects their health, so read on.        

Effects of Secondhand Marijuana Smoke

Inhaling secondhand marijuana smoke is similar to tobacco smoke exposure. Both cannabis smoke and tobacco smoke have carcinogenic components, so naturally, it isn’t a good idea to stay in an unventilated room filled with cannabis smoke for a long period. We know that tobacco smoke exposure is especially harmful to children, so marijuana smoke won’t be any different. 

Secondhand cannabis smoke won’t result in a “contact high” according to a 2010 study done at Amsterdam coffeeshops, however, you may absorb a small amount of THC. Another study done at the Johns Hopkins University School of Medicine researched the effects of secondhand exposure to cannabis smoke, and it also proved that staying in a room where people smoke weed won’t get you high. 

This claim was also confirmed by the National Institute on Drug Abuse (NIDA), which researched the potency of the drug as well as room ventilation and hours of exposure. The organization claimed that a contact high wasn’t possible from secondhand exposure, though nonsmokers may experience other side effects.

What Are the Health Risks From Staying in an Unventilated Room?

  • Secondhand exposure to cannabis in an unventilated room is linked to some performance impairments which may affect driving skills, which is why you should wait a few hours if you’re feeling unwell (after your exposure to weed smoke).
  • Secondhand cannabis exposure may also affect the function of blood vessels and the effects may even last longer than inhaling secondhand tobacco smoke. According to an animal study, inhaling pot smoke secondhand can shrink the blood vessels in mice similar to how tobacco smoke does. However, this study hasn’t been done on humans, so there’s no final answer on this subject.
  • Inhaling secondhand marijuana smoke may affect lung health in the long-term for people who are staying in unventilated rooms often.

Keep in mind that these effects are often a result of long-term exposure to secondhand cannabis smoke. If you find yourself in a room where a lot of people are vaping or smoking weed just one time, you definitely won’t experience lasting effects.

Can You Fail a Drug Test From Secondhand Cannabis Smoke?

As recreational marijuana and medical marijuana consumption have increased around the US, so has mandatory workplace drug testing. Drug tests check for the presence of cannabinoids by testing the levels of tetrahydrocannabinol (THC) and its byproducts known as THC metabolites in the body. Common cannabis drug tests include:

  • Oral fluid test;
  • Blood test;
  • Urine test
  • Hair follicle test.

According to the studies mentioned above, it’s almost impossible to get a positive drug test result from secondhand cannabis exposure. On rare occasions, people who are tested immediately after exposure could have a positive urine test, however, the chances of that happening are slim. An oral fluid test may be positive after secondhand cannabis exposure if you get tested within 30 minutes after the exposure, according to research.

The positive result on a drug screen can also depend on:

  • How long you’ve stayed in an unventilated room;
  • How often you’re exposed to secondhand marijuana smoke;
  • How much time has passed after your exposure;
  • How sensitive the drug test is.

While it’s very unlikely that you’ll get a positive drug test from secondhand exposure, some tests can be more sensitive than others, so if you’re tested with a very sensitive test immediately after exposure, you may get a positive result. However, the cutoff for most standard drug tests is 50 nanograms per milliliter (ng/mL), so the amount of THC in the body should be above this number in order for you to get a positive result.

What to Do if You Find Yourself in a Room Where People Smoke Pot?

Sometimes you find yourself in a situation where the only one who isn’t smoking weed is yourself. Naturally, you want to keep the secondhand exposure to a minimum, so what do you do? 

The best option would be to kindly ask the marijuana smokers to keep a door or a window open to provide natural airflow. And if the weather is too cold, make sure you air the room at 15-20 minute intervals. 

How to Get Rid Of Secondhand Marijuana Smoke From Your System?

There are a few methods you can use besides staying in a ventilated room to get rid of secondhand marijuana smoke from your body.

  • You can drink more water, as this is the most natural method that the body detoxes itself. This will not only keep you hydrated, but it will also dilute the urine if you need to take a drug test. You can take Vitamin B, if you want, as this will improve the appearance of your urine (so it won’t seem diluted when you drink a lot of water).
  • A Zinc supplement can also help you dilute the THC metabolites and make them harder to detect, so it can also be an option if you’re in a hurry.
  • Consuming activated charcoal also helps eliminate unwanted substances from the body, so consuming it may help you get rid of the unwanted THC metabolites you got from smelling weed.

Please keep in mind that consuming pills and other medications should never be done without the consultation of a healthcare provider, especially if you’re taking some kind of therapy. 

Final Thoughts 

As you’ve probably concluded by now, smelling weed isn’t likely to cause a positive drug test among passive cannabis smokers. The trace amounts of THC metabolites which may accumulate in your body after passive exposure to cannabis smoke won’t be detected by standard drug tests which have a threshold of the 50 nanograms per milliliter (ng/mL).

The only way you could test positive is if you get tested immediately after exposure with a very sensitive drug test, and the chances of that happening are actually very slim.

Still, to avoid any chances of exposure, you can socialize in a ventilated room (and sit far away from the marijuana smokers). This way you’ll limit your exposure, as well as the possible side effects.

Additional Sources

NIDA. 2020, October 13. Secondhand Marijuana Smoke?. Retrieved from https://teens.drugabuse.gov/blog/post/secondhand-marijuana-smoke-update

Herrmann, E. S., Cone, E. J., Mitchell, J. M., Bigelow, G. E., LoDico, C., Flegel, R., & Vandrey, R. (2015). Non-smoker exposure to secondhand cannabis smoke II: Effect of room ventilation on the physiological, subjective, and behavioral/cognitive effects. Drug and alcohol dependence, 151, 194–202. https://doi.org/10.1016/j.drugalcdep.2015.03.019

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.


The information presented on this page is provided as a public service to aid in education and is derived from sources believed to be reliable. Readers are responsible for making their own assessment of the topics discussed here. In no event shall Leaf Nation be held reliable for any injury, loss or damage that could happen if using or abusing drugs.