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.


omg weed no good. weed badddddd
weed is not good for you
weed is not good for u including on my hypothesis it is very bad it you can get a brain disease. but it helps me ;)
Weed is no worse than the drugs doctors push like Xanax, Vicodin and not to mention the drugs they test for a month or two. Than we see these commercials about if you have taken this drug and got cancer, had a stroke and so on! Weed has been around for hundreds of years and smoked as rituals and to relax, the only effects I have ever read about was the giggles, munchies, sleepy, and relaxed. This drug helps many people and alcohol and cigarettes are worse for you! If you don't like it don't use it, but keep your nose out of my business at home when I'm not at work.
Comparing it to other bad stuff that is out there does not make more safe. Did you know shooting yourself in the head is also bad and can possibly lead to death, therefore, weed is good. Uuummm. I think not
There have been no studies that suggest weed is bad for you. If you can provide facts from studies please post the links so the rest of us can see them. Oh wait, you won't find any.

You can read about some of the most recent research on both the adverse health effects and the potential therapeutic benefits linked to marijuana here: http://www.drugabuse.gov/publications/research-reports/marijuana/letter-...

There was a study done in jamaca on weed and children 20 mothers smoked during there pregnancy and the first five years of the child's life 20 other mothers did the opposite the kids that's parents smoked pot where found to develop faster and learn faster. The study only lasted five years because they stopped the funding when they couldn't prove that it effected the children in any way negatively. On top of that it has around 25 or so medical use to treat illnesses without the use of prescription pills that cause liver damage and a dependency on a different scale then weeds. And the damage cause by those pills gets treated with more pills. When in some cases they could have smoked a joint. And I know people how have smoked weed for fifty years and are in better health then the people who never smoked it.
See if you want to smoke your weed that is fine. But on that note why should I have to smell it while at or leaving a MLB game. There were a lot of kids and Air Force people their and if somehow we pop positive for THC from repetitive encounters with the weed then we could lose our jobs. My 10 year old sister in law should not have to walk through that and neither should I. If you want to smoke your weed smoke it somewhere more private. That's all I am saying.
I like this argument and agree. People should not be forced to smell our decision. If you want to do it in family setting then learn to make it odorless.
Actually some people have an adverse reaction to weed, and it really gets me that people self diagnose themselves with anxiety and claim that pot helps, when I can tell you from my own personal experience that people who truly have anxiety are more likely to experience panic attacks due to pot use rather than any kind of relaxed feeling. It just really gets me that everyone always assumes that other people have the same reaction to something that they do. I just breathed in a small secondhand amount while walking home and I am still feeling nauseous and upset an hour later. I hate that people are forcing me to experience something that I want no part of. And yes THC is still present in secondhand smoke therefore it is still entering your body and affecting your mind even if in small amounts.
I agree! We get second hand smoke and/sometimes or/ just the smell of it through our AC vent from the connecting apartment. The smell itself annoys me, but I hate that I have to choose between being comfortable in my own apartment and not having a panic attack or a headache/nauseated and dizzy... The scumlord told me to buy an airfreshner... really!
I have really bad axiety and PTSD due to a rape and have medical marijuana prescribed and it actually helps my ptsd episodes and my anxiety alot .
"It just really gets me that everyone always assumes that other people have the same reaction to something that they do." Couple of generalizations here. Not "everyone always assumes", and aren't you essentially saying that you have anxiety and know that everyone should react the same way as you, because you have anxiety and know? I have anxiety, ptsd and depression. Sometimes pot helps, sometimes it doesn't. But it never harms me. So I would be an exception to your rule. To each his own, we are all different. Please do not preach or generalize. Only you are you.
I would say no no no because me no likey marijuana
Yep. Me too, and I'm not taking any chances in using or inhaling the smoke from marijuana. We might not know for sure whether it helps human health, but one thing for sure is that marijuana corrupts our body. Just please, DON'T use marijuana.
Whenever you say ''studies'', please include a source. I'm curious.

Hi Anonymous, we've linked to the studies in the post.  Please check them out.

I was given a hair test on 2-13-15 and failed for THC under 50ng. I retested under my own dollar and i came up negative. I lost my job behind this situation and I'm going in for the jugular.
There is over a billion scientist giving everybody the true facts on marijuana not only does it harm you but it can also help you it does more bad than good stop being ignoret get the facts.
ignorant? *ARE there even a billion scientists alive in the world right now? are false facts a real thing even? good lord, smoke some weed man
I am a baker and every morning i have a poppy seed bagel for breakfast and work with a lot of poppy seeds could it come up in my saliva drug test as positive for marijuana

Hi Chef Greg.  Eating poppy seed might cause you to test positive for opiates—not marijuana.  Check out our post Drug Testing for ... Poppy Seeds for more information.

I used to smoke ans got put on probation. I was around a music festival for one day (full of weed) and hang around a family member who smokes in his house but in another room. Long story short I failed my drug hair test today and im wondering how that happened considering I never smoked
When exposed like that. And that specifiuc method of testing. It can go back a looong time. Most courts dnt even allow this. Unless its a child in a dhs case usuaslly. Let your lawyer know youve smoked in the past year and thats not fair. Because hair testing. Is stupid.
It doesn't matter I u smoked it or not if your by people that smoke its gunna be in your hair for a long time
Im enlisted in the navy and have a drug test coming up in about a week. My cousin has been smoking weed in our room, the window was open and a fan was on but the odor was strong enough to get him caught, i want to prove to my parents i didnt smoke but am afraid that i may fail a drug test. I was only exposed for about an hour when i moved another room in my house to sleep. Im very nervous and would appreciate any feedback.

Hi lumpy.  Based on what you describe above, it's not likely that you inhaled enough secondhand marijuna smoke to fail a drug test.  Good luck!

You can have traces of cannibis in the military drug screen. They account for exposure. They look at levels. I can't say the same for civilian company drug testing
I'm going to MEPs Thursday , and I will be taking a drug test ... I have been around friends who were smoking lightly on 2 different days for about 5 hrs a day, cause we were gambling ; I don't have any doubts that I'll fail but I'm wondering
Hello ,my fiance smokes often a lot of times in my presence how will this effect me ?

Unfortunately, KammyK, we don't know much about how secondhand smoke affects people.  We suspect it is similar to secondhand cigarette smoke, but we're waiting for research to know for sure.  

I have a quston about to things my old laddie just had a baby and but does not do no drugs at all I smoke weed well before she had baby she got drug tested and methinphedinms in her system then she has the baby few days later which was to days ago And did another the same thing came up then today she has weed in her system and no methinphedimns was found now how the hack do u get weed in your system if u been in the hospital and the pevoiusly drug test there was none

Hi Adam, we can't speak to this person's drug test results specifically. Please talk to a doctor if you have concerns.

I was with a friend who was giving someone a shot gun not the inhaled kind some of the smoke got into my mouth because I was by her (she was giving her dog a shotgun) will I fail my drug screen next week? I'm in intensive probation and I don't want to go to jail for this I have been drug free for over a year now I literally just unfriend my bff because of this. Did I overreact?

You did not overact. It is a good idea to be cautious about your exposure to drugs, especially because of your intensive probation. It’s not likely that you will fail a drug test due to secondhand marijuana smoke exposure. But, if you know you’re going to have to take drug tests, you should try to avoid places, people, and situations that could lead to exposure.

higuys im going to the army's first recuitment soon and thats the story last friday u smoked like 5-7 inhales of a joint and i remember theres that urien check 18 days later. (as far as i know its a normal check and not drug test) might they still find it?i workout so i pee and sweat alot. another thing is im at this concert and some ppl lighted a joint and i can smell the weed very boldly, is it second hand? im very worried of that urien check. will they find thc17- 18 days of intese peeing and prolly some smelling in a concert? im very very worried im really looking farward an aswer please answer me asap :(

Hi Yanko.  Unfortunately, we can't answer that for you.  Everyone is different and many factors influence whether marijuana will show up in a drug test, including your size, how often you've smoked, how much you smoked, when you smoked, etc.  It's not likely that the secondhand smoke from the concert will affect your urine test, but we can't say the same for smoking last Friday.  

Hi, i was at a friends party outside and all of theMwere smoking weed this was on jan 3. I just took a hair drug test in jan 22 could secondhand smoke of marijuana show up onony hair drug test .

Hi Brittany, as long as you weren't smoking, it's not likely.

Is there any fact to this. Because I am in the same position but it was blown in my face once and thats the only time I was even been near it.
These people don't know what they are talking about! I've never smoked in my life but was around someone for maybe 30 mins who was smoking in a ventilated area but I could still smell it strongly and I failed my hair test 2 weeks later!! And to top it off I'm pregnant and if I was going to try it for the first time it definately wouldn't be now!
Hey. I was inside a house party. The living room. Everybody was smoking an I wasnt. The room was packed with second hand smoke but every hour or so I would step outside for a few minutes. There was over 30 people in the party also. Is it possible it could of got in my system ?

It's possible that a very, very small amount got into your system, but not enough to get you "high" or cause you to fail a drug test.

Hi, I have to get a drug test for work but on the the 13 I was In a car with my friend for only 30 mins that was smoking would I fail my drug test because of that

It's not likely—though you should try to avoid situations like that in the future.  Secondhand smoke isn't healthy.  Good luck with the new job.

I was in a car of a weed smoker with my window down while they smoke for about 45min took a drug 3day later will I test positive for the drug test

No, probably not.  

i have upcoming dr's appointment and he normally does drug test, i dont smoke so i have not worried about but lately i have been around a person that does never thinking about my upcoming test will this cause me to fail my urine test
I have grand children who's parent smokes weed .I am worried about the second hand smell effect. What should I do ?


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