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 the use of the cannabis plant and more are expected to follow in the next few years. The increased legalization rates have brought on more research into how cannabis affects users but also passive smokers. 

People who don’t smoke weed but often find themselves in rooms where cannabis smokers are having a smoking session are sometimes wondering whether smelling weed will result in a positive drug test. They assume that being in a hotboxing room for a long period of time will increase their levels of THC, resulting in a secondhand high. To set the record straight, in this article, we’ll get into how marijuana use affects non-smokers, whether weed smoke could get passive smokers high, and everything else you can think of related to the subject.

Effects of Secondhand Marijuana Smoke

Inhaling secondhand marijuana smoke is much like inhaling secondhand cigarette smoke. Cannabis smoke, similar to tobacco smoke, has carcinogenic properties, so it’s not an ideal scenario to stay in unventilated rooms filled with weed smoke for long periods of time. While inhaling both cannabis smoke and tobacco smoke is harmful, cannabis smoke isn’t as carcinogenic as tobacco smoke according to a study done in 2005. That being said, tobacco smoke exposure is extremely harmful to children and so is marijuana smoke, so never leave your children in an unventilated room where cannabis is smoked.

The Risks of Staying in an Unventilated Room Where Cannabis Is Smoked

It isn’t recommended that you stay in a room where cannabis is smoked for long periods of time, especially if the room is unventilated, for a number of reasons:

  • Even one minute of marijuana secondhand smoke exposure substantially impairs vascular endothelial function, according to a study.
  • Secondhand exposure to cannabis is linked to impairments in your ability to drive a car safely, which is why you should wait for the effects to pass before you get back to your car and get on the road.
  • Inhaling secondhand smoke with high levels of THC, CBD, other cannabinoids, and chemical compounds can affect your lung health long-term.

These effects aren’t likely to significantly impair your health if you occasionally stay in a room where people are smoking weed or vaping, but the secondhand smoke does still pose some major health concerns.

Is Getting High From Secondhand Cannabis Smoke Likely?

While it isn’t likely that you’ll get high from smelling weed when staying in a room where people are smoking the cannabis flower, there are some risks of getting a positive drug test in some cases. While the terpenes are responsible for the strong smell of weed, the cannabinoids are responsible for the effects of weed on your body, such as the psychoactive effects that THC produces. 

You probably know that drug tests check for the presence of the metabolites of the cannabinoid THC in your saliva, blood, urine, or hair. Depending on the type of cannabis strain your friends bought from the dispensary and its THC content, as well as how often and how long you’ve been exposed to secondhand marijuana smoke in an unventilated room or how sensitive the drug test is, you may get a positive result on rare occasions.

According to research, an oral fluid drug test can be positive for 30 minutes after exposure to secondhand cannabis smoke. Another study done in 2015 by the John Hopkins University School of Medicine concluded that while you can experience side effects from secondhand exposure to cannabis, a contact high isn’t one of them. Despite this, one of the people tested had a positive urine drug test compared with the federal cutoff levels which is 50 ng/mL.

According to a 2010 study on “contact high” done on people who stayed in coffee shops, only a small amount of THC was absorbed which means it’s unlikely that you’ll get a positive urine drug test. However, some of the blood tests done after the initial exposure showed traces of THC-COOH.

According to an article by the National Institute on Drug Abuse, staying in an unventilated room where people are smoking cannabis for a long period of time may result in a “contact high” on rare occasions. For that reason, it’s best to kindly ask your friends to ventilate the room regularly so you can keep the secondhand exposure to a minimum. It’s optimal to let the room air out at 15 to 20-minute intervals.

Eliminate Secondhand Marijuana Smoke From Your System

Let’s say that you’ve inhaled a significant amount of secondhand cannabis smoke and you’re worried that it may show up on your mandatory drug test at work. What do you do then? While we don’t guarantee that these methods will work 100% and are not encouraging cheating on drug tests, below are some methods to detox naturally from secondhand weed smoke.

To promote natural detoxing, you can always drink more water and keep yourself hydrated. While drinking significant amounts of water can dilute your urine and make it look suspicious, you can always take a B vitamin to improve the appearance of your urine.

Another supplement that you can take to help dilute THC metabolites in your body is zinc which is also a supplement that has numerous other benefits for your body, hair, and skin. You can also take some activated charcoal which can help in the elimination of a number of substances and toxins from your body, and you can use it to promote the detox from lingering THC metabolites.

Don’t take any medication or pills intended for detox that aren’t in the realm of normal doses of vitamins and minerals without a consultation with your healthcare provider. This can only harm you in the long term, especially if you’re taking therapy for a medical condition.

Final Thoughts

You know by now that smelling weed isn’t likely to result in a positive drug test or a high if you’re staying in an unventilated room where cannabis is smoked. After all, small amounts of THC metabolites that accumulate in your body after passive exposure to cannabis aren’t detected by most standard drug tests with a threshold for cannabis of 50 nanograms per milliliter (ng/mL).

You can only test positive if you’re tested using a very sensitive drug test immediately after exposure. And with regards to getting “contact high,” any effects that you experience post exposure to secondhand cannabis will wear off in a few hours. Remember not to operate heavy machinery or drive if you aren’t feeling your best. 

To prevent secondhand cannabis exposure and all the side effects that come with it in the future, make sure that you’re socializing in a ventilated room which is aired out every 15 to 20 minutes. It’s also a good idea not to sit immediately next to cannabis smokers so you limit the exposure and the side effects as much as you can. So the next time you get together with your friends, take the seat closest to the door or window and open it regularly.

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.