Drugs & Health Blog

Secondhand Marijuana Smoke?

The NIDA Blog Team

In concerts, at house parties, even in the hallway of apartment buildings, you may have come into contact and been exposed to secondhand marijuana smoke.

In situations like these, people often worry how breathing someone else’s marijuana smoke affects them.  A couple of common questions and the answers may help you see through the fog of this smoky situation.

Can you get high from inhaling secondhand marijuana smoke?

Probably not. 

You may have heard the phrase “contact high,” about someone breathing secondhand marijuana smoke and feeling a buzz. Studies have found that in extreme conditions, with lots of smoke blown directly into your face, you can feel the high and it can even show up in a urine test. But this is not a normal circumstance.

Research shows that very little THC is exhaled back into the air when a smoker exhales. So little, in fact, that if you sat in a room while people exhaled the smoke of four marijuana cigarettes (sometimes called joints) in one hour, you wouldn’t get high.  You would have to be trapped in a room breathing the smoke of 16 burning joints before you started to show signs of being high. 

Can you fail a drug test from inhaling secondhand marijuana smoke?

Again, probably not.

Since the amount of THC exhaled by marijuana smokers is so low, it would take a lot of secondhand exposure to fail a drug test. 

In a 2010 study, researchers measured the effect of secondhand marijuana smoke on non-marijuana smokers.  The non-smokers were placed in a well-ventilated space with people casually smoking marijuana for 3 hours.  The researchers then took blood and urine samples from the nonsmokers. They found that THC was present, but the amount was well below the level to needed to fail a drug test.  Another study found similar results: Testing positive is rare and limited to the hours directly following exposure.

What are the health effects of inhaling secondhand marijuana smoke?

Researchers are still working to figure this out. We still don’t know how a person is affected if they live with a regular marijuana smoker. We also don’t know how higher amounts of THC in today’s marijuana cigarettes affects secondhand smoke.

A recent study on rats suggests that secondhand marijuana smoke can do as much damage to your heart and blood vessels as secondhand tobacco smoke. But that study has not yet been done on humans.

We also know marijuana smoke contains harmful and cancer-causing chemicals, the same way tobacco smoke does. But we still don’t know how it affects a person’s health in the long run. Lots more research still needs to be done. 

Tell us in comments: what would you do if someone was smoking marijuana near you?

Update: Read the blog post, “Two More Things We’ve Learned About Secondhand Marijuana Smoke.”

Comments posted to the Drugs & Health Blog are from the general public and may contain inaccurate information. They do not represent the views of NIDA or any other federal government entity.


Hi i go over to my friends house and they smoke alot of weed thier in a garage we open the door or garage door alot but i can still smell it heavily i would cover myself with my shirt or sweater i have meps on thursday will Marijuana show up in my results and i wanted to know if the walmart drug test are reliable i just wanted to take one to make sure please respond thank you
Yes they are. My partner has used them many times in the past to see if he would pass, and they've always been reliable for him. :) at least for marijuana. He's never had to use any other ones. Lol.
Would second hand marijuana show in a hair test?
Ugh. Another website for teenagers with lies. marijuana does not have cancer causing chemicals in the smoke. My friends have been smoking marijuana for over 50 years and they are still the healthiest people I know. Even healthier then me.
I know. I've been reading these comments slapping my forehead every five seconds. People saying weed is sooooo bad for you.. The only thing that's really "bad" about it is smoking it. But there are MANY other methods..
Somebody blew marijuana smoke into my face (I'm not a smoker) and I caught the giggles. Asking my friend why the sky was blue and not any other colour... So, I guess it can affect others around them. Perhaps to a certain degree, depending how exposed you are to it?
im in perfect health and I have smoked weed for 55 years
Sang, great logic. Sounds about the same as the my granddad smoked cigarettes all his life since he was 15 and he is in perfect health for 80 years old. Some people bite the bullet and others don't.
Hi. Someone in my house was smoking weed 2 nights in a row in the living room, while I was up stairs in my room... I went downstairs real quick both nights, I'm wondering if this will affect my chances of a the drug test?
My husband and i don't smoke weed but we let someone smoke in our house a couple of time because she didn't want the neighbors to see her. now my husband has to have a drug test for work. Should we worry about him failing?
I would like to know the same
Hi I am a second hand smoker of marijuana,...the effect of marijuana has effected me in many ways. My mind feel if though i'd applied heavy emphasis on everything that comes to mind,...I also appoach situation annoyance behavior when the smoke is burning. Health wise my oil glands (eyes) are now dried. When I'm cleared from the smoke I feel the pop of clearance to mind,...I'm more proactive in my duties.
Hey guys I was with a couple of friends last night, and we we were in a tent just chilling. Then my friends went outside the tent to smoke joints and I think a tiny bit of it blew inside, I had a quick scent of it. Was just wondering if briefly smelling it would come up as a positive reading on a urine test? Thanks :)
Smelt marijuana on someone's breath. Harmful?
I just want to put my opinion across, I stopped smoking weed about 30 days before joining the merch can't navy, I had a drug test a week after joining, everyday up until the intake I would have several friends (5-7) all smoking there own joins in the same room as me for 6 hours a day, not A trace of cannabis was found in my system on my drug test, luckily for me I have a very fast metabolism that could have contributed to me passing the test with flying colours, however. I failed a second drug test a year later because I had been smoking weed for a good 2 weeks and only stopped 2 days before that drug test, I failed with 0.42 mg of cannabis in my urine, a doctor said to me that if it had been 0.35 mg of cabbis in my urine then they could not be sure if I had smoked it or if it was because of passive smoking, I hope this is of use to somebody, please note I cared not about loosing that job in the end, hence the reason for smoking. In fact it was actually better to fail a drug test or pay £6000 for leaving haha, I have a better job now and have since had to stop smoking again, to all the haters of cannbis, it is a natural plant, and has been proved to help cure some cancers, as well as help people with eating/sleeping disorders and many more.
Ok.....now here is the answer to all your drug questions...the army has just changed its policy at meps now if you piss positive for drugs of any kind you are TEMPORARY DQ for 90 days..marijuana stays in your system for about 30 days if your are not excessively over weight, because the molecules of marijuana sticks to fatty cells in your body. It is best if you let your military recruiter know when you last smoke, in some branch they have gotten ride of drug testing in the office so their is no way for them recruiters to know if you are positive
Reading through this comment thread was so brutal, the levels of ignorance of cannabinoid science and the human endocannabinoid system are astounding. And btw, NIDA, cannabis smoke does not, and has not, caused cancer. Please don't convey information in a slanted fashion.
I have a urine drug test today. While I did not smoke any marijuana, last week I had a joint in my pack of cigarettes and when I smoked the cigarettes, I could smell the aroma of the marijuana on my cigarettes, but I never actually smoked the joint. So will I fail the urine test from smoking the cigarettes that were next to the joint?

It's not likely.

Hi i have a tenant who smokes something dontknow wat exatly. I know cigarette smell but this is different he smokes past midnight i have no smoking polici but that is not stoping him i gat up. Past 2 oclock am and he is smoking something the smell comes up thru the vents my quedtion is how can i report him ,how is effecting. Me my health.thanks ,also i saw in his garbage a drug test ,so i have proof ,,,,
Hi I haven't been smoking for about one and a half months but I still am Around people who do smoke about 4 times a week every week since then, I do try avoid to breath in the smoke since we are outside but I can still smell the smoke after, I need to take a drug test soon and I'm not sure how it will show up as?
Look at it for what it is a plant God pus on this earth religious freedom not govt restriction comparing pills to a natural psychoactive chemical is like comparing knives to guns free will is good if I want to do something that doesn't harm anyone else then who are you to tell me I can't do it do what your parents taught you and mind your own alcohol and cigarettes is legal and man made and doesn't get a second look but if the guy next to you say weed is bad cuz the govt says it's illegal is crazy to me
My brother smokes a lot we hen my dad isnt home. Instead of relaxed he seems more ignorant, tense, unreasonable, and has this face where he looks like he wants to kill someone ALL the time. I told my mom and dad, but they say marijuana only calms you down. It seems to affect me too, because he smokes in the room we sleep in! Also I seem to be more responsible and rational than him and he's older. Please, please, please give me some feedback.

Hi Call911, if you want to talk to somebody, please call 1-800-273-8255. The phone line is run by SAMHSA, and they have people standing by at all hours to talk about any problems you're dealing with. They also have an online chat line you can access here: http://www.suicidepreventionlifeline.org/

Oh thank god! I've been worrying about this a lot because I have job interview coming up. I quit smoking a LONG time ago, but my fiancee didn't. Every time I've smelled it recently I've covered my face freaking out thinking if I inhale it I'm gonna fail my DT! Lol. Good to know I got no worries. :) thanks for this!
Hey I have to take a drug test tomorrow to swear into the navy and about a hr ago I was with a friend who smoked a blunt of loud Marijuana while I was braiding her hair will I fail my test tomorrow...and sn:that's the first time in about a year I have been exposed to smoke from the drug

Hi lula, it's not likely that you could inhale enough secondhand marijuana smoke to fail a drug test. 

I was in the back seats of the car ,and my two friends in the front car seat the smoke was about to start filling the car and I got out will I test positive on the drug test ??

Hi Cece, it's not likely that you could inhale enough secondhand marijuana smoke to fail a drug test.

Whoever wrote this article is an idiot. You Will in fact test positive for THC if you are exposed to marijuana smoke even in the smallest amounts. Try it and see
I have to take a drug test in a couple days. I was wondering would I fail a drug test by just being around second hand weed smoke in a car for only about 15 mins? while I was in the car the two ppl in the front were smoking but they only smoked one blunt and my window in the back seat of the car was a little cracked open.

Probably not.

I dont smoke marijuana havent for a while because I drive trucks & you get tested all the time. I got drug tested today & failed for THC I could lose my job. I hang around alot of people that smoke all the time in the living room. I don't have nothing against the drug cause it helps people in different ways
Was sitting at the beach and these people were lighting a fatty and blew it over by us but I didn't smoke but failed my drug test. Wtf
I'm at a double edged sword. I smoked for over 30 years, did some time and to top it off, was also diagnosed with a brain tumor 8 years ago. I have been totally clean and sober for 7 years, but have also tested positive for thc 3x!! And I have all tests but 1,from 18 yrs ago in a situation where those people personally told my Dr that in fact I DID NOT smoke. I have ALSO been told by her( my Dr) that given my situation, thc can help, but almost all tumor was removed last August. I will also never have a shot at decent employment after college;a masters degree still cannot help getting a job. I do not WANT to smoke. But people might want to realize that POSSIBLY, some of us will test positive more than others from 2nd hand. Last year I breathed it constantly, every day. Tested positive. Told my Dr I was moving into a house with a family member, who rarely smokes in the same room. Rarely does not mean NEVER..there was second hand smoke 4-5x and??Ill know this week..until scientific research gives exact results, the best way is to stay away from smokers, and if needed check out the other thc uses for medical issues. We CAN have help without being stoned
I got the hell away, my future depends on not failing and drug test. And lest time I check weed is still an illegal substance in 49 of the 50 states
Wrong medicinal weed use is legal in 24 of 50 states, recreational use is allowed in 3 I think , but you have small towns that have made it legal scattered around the United States.. Not trying to start a argument, just giving out facts for those who truly don't know, Colorado an California an Washington, D.C.
My boys whole family smokes he sits in the room with his brother while he smokes he has never failed his probation drug test ever and they smoke every day
If you don't smoke weed and someone else is ssmoking it how long does it take it to get out of your blood if you take blood work
I just think that the smell is nasty and makes me gag and choke, I just wanted to know if It would give you chest pains, being exposed to the smoke.

There has been a lot of research on the effects of secondhand tobacco smoke, but we currently don’t know very much about the effects of secondhand marijuana smoke. But just because there isn’t much research yet on it, doesn’t mean you should allow yourself to be exposed to it—especially when you find it physically uncomfortable. After all, it took decades to link tobacco to cancer and lunch and heart disease, in both smokers and those who were exposed to smoke.

My son has been exposed to secondhand marijuana smoke while visiting family. We have a child custody order specifically prohibiting marijuana. If I test him and it comes back hot, what do I need to do?

We’re sorry to hear that your son may be exposed to secondhand smoke. Positive drug tests are rare for people exposed only secondhand to marijuana smoke, but might be higher for a child. We also do not know what affect secondhand smoke might have on a child’s developing brain. If you get a positive test, we recommend you consult a physician as well as whatever support system is in place to protect your child.

My question is if someone is smoking a blunt and is blowing right in ur face and you can see smoke coming out of your mouth but your not actually hitting the blunt isn't that just as bad and will it show up on a drug test?

Positive drug tests are rare for people exposed only secondhand to marijuana smoke. Studies show that smoke would have to be blown directly into your face for a long period of time to show up on a drug test. It is possible, but most real life situations are not like that. How likely secondhand smoke is to impact a bystander’s drug test depends on the ventilation of the room, the amount of THC content of the marijuana being smoked (how strong it is), how much smoke someone is exposed to, for how long, and how long after that exposure a drug test is administered.

You know, people next my room smoke, and I do smoke before too actually but I stopped and am concerned about not in hailing at all
At a concert where several people were lighting up, bowls, joints, and I didn't get high.
weed can really noid some folks out, some folks they love the effects, it's easy to fix those who like it and those who don't, show some good old common deacenty 2 each other till the science is in,i don't but peace out to the smoochie buchies!
Right well..I once sat in a car, together with two people smoking a joint, and after it was done, they smoked another. The windows were up, we could barely see trough the windows (don't judge me, it wasn't my idea, I know that is dangerous, I protested) and we were in there for an hour. After that, I felt like vomiting and had a terrible headache. The last few minutes in the car I got tired and drowzy and had the feeling the waterdrops on the window had little faces and were smiling at me. Now..I am known for overreacting to normal medicines. Last time I took a sleepingpill, meant for people that overreact to melatonine, so it had the lowest dose in the freaking world. And still I was tripping balls that night and hallucinated the whole carnival in my bedroom. But still, you can't even try claiming that it won't have any effect on you.
It happened to me last night and I literally was like "I'm going, goodnight everyone" and I walked home in the dark. Better off walking in the dark than being around drugs. I'm a "follow the rules" kind of person. I don't do drugs, and I never will. I have never smoked and never will, I don't like drinking and yet I still manage to have fun. My upbringing was simple yet I knew what was okay and what was not okay.


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