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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?

Learn more: marijuana withdrawal is real.

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.


get da heck out of there
It was in my dorm room, nothing i can do about it
SAME!!!!!! literally RIP
If you have a problem with Marijuana smokers in a dorm room or an apartment building do what I have done and call the police and have them arrested. It's still against the law even under your own roof if it effects others. I cleaned out my entire apartment building. I have kids so I do not want the exposed to it especially on a normal basis. I even Remember there is always something that you can do nothing is beyond your power if you want it or want to accomplish something.
What state is this?? I leave in L.A and police keeps saying that there's little they can do. I have a 3year old son.
I live in Scotland and the person down stairs smokes weed most off the time flat stinks and I have a 2 year old grandson who inhales it all the time when they smoke down stairs we don't like it Next step is calling the police to see if they can help

Second hand smoke of any drug is not healthy for a 2 year old, whose brain and lungs are developing. For adults, it is not likely to make you “high” despite the myths of a ”contact high” but it can affect your lungs and breathing and can make your life miserable to smell it all the time. It is similar to non smokers who have to live in a building alongside cigarette smokers---it can be very uncomfortable. See

Be careful with that. That's good but understand there are people that will kill you and your family for calling the cops. You may think your helping but in all reality your putting you and you family in dangerm
That's true but how would they know who called? I am sure it was anonymous!
are all of you cracy nobodys gonna kill over some weed
the calls are not anonymous especially in florida. they can tell the person you called.
I doubt shes afraid of a bunch of potheads. They'll light up and forget the cops were ever there.
Snitch its jus weed!! Why do so many people hate the smell.
Because it smells like a skunk landed right in front of you....that's why!!!
So true. Potheads can't smell. So that's why it doesn't bother them.
True true, even cigarette smokers lose their sense of smell. My dad smoked cigarettes and weed for years and years ayears and said when he stopped both that his sense of smell and taste where extremely better.
Not True myself a notorious pothead love the smell as mot potheads do thepotheadtifficus also love the raw smell of bud Doritos and especially chocolate and cannot understand why people don't like they smell as each kind has a different smell
Exactly I'm 12 and my dad smoked weed it's down right disgusting and I've almost fanted you People who don't care for children breathing it in are just jealous cause your stuck in the addition of weed or other drugs
Good for you, Dillon, to know how bad it is at such a young age. Don't forget when you are older.
It ruins your clothes, distracts you from doing studies, it stinks, gives people that don't smoke a headache and I'm paying rent and don't want to be exposed to it. Oh and it kills your brain Ella.
It doesn't kill brain cells. That's a myth that has been dispelled.
Untrue in fact it has been repeatedly proven to delay and halt the forming of the adult brain.....
Well I have a doctorate and a successful practice and two undergrad degrees and I smoked the whole time. Soooo... check your facts. Also, many professionals and CEO's of companies smoke and do other drugs on a daily basis. People are ignorant. Not every pot smoker is a Loser. Oh yea my dads a physician and smoked as a teen as well smh. What do you upstanding citizens do? haha
Marijuana destroys all ambition. Kinda like a form of mental castration. And like all forms of addiction, addicts will always extrapulate and find justification for their drug use.
It paralyzes them instead! Not much better. I have loved ones who smoke everyday, multiple times a day, and some who smoke a few times a week. They all show signs that their thought process, and memory are majorly effected. I smoked pot last year 1 time for the 1st time in like 10 years. I was noticably effected for about 3 days after smoking!
The effects only stay for a few hours then leave. You must of taken something to have an effect that last 3 days or are overdramatizing about it. You'd have to be in the same room for hours with poor ventilation with tons of marijuana smokers to feel any effects to it.
It does kill brain cells they just redevelop faster than they can be killed
Funny how many "grays anatomy" doctors we have here. Lies lies lies.
I absolutely agree with you. I am severely allergic to cigarette smoke and my body reacts to this the same. I pay rent as well and should not walk in from work to this smell in my space or in my blood.
It only ruins your clothes if you dont wash them and take care of them not because of marijuana. Go hang out with people like you. Hence.. Not in this country bud
Yes! Thank neighbor smokes enormous amounts and it stinks so bad. I was wondering why I had a headache this morning...
Yes it does gives you headache and sometimes sick to the stomach
I use to smoke it. Now it stinks to me worse than somebody having a cigarette and I smoke cigarettes but have had to go for 3 days without smoking and when I was around cigarette smell I got sick so had one. Weed smell is alot different and people need to have respect for others and not do it where they live. Weed is still illegal with federal law. State law might make it okay but Federal can come in and take every single one of y'all to jail for smoking
call the FBI I'm sure they would love to arrest someone for pot when they could be saving other people's lives insted instead of wasting their time...
Pot in the legal community is a BIG money maker! It will suck your finaces dry and/or retirement. Marajana will always remain illegal.
Cigarette smoke is worse my head spins off when I smell that mess but weed don't effect me like that in fact to get of that headache....join them
I don't smoke and I totally believe it has many medical properties that help sick people. Our society has been brainwashed over the years to believe that it is bad for us. Alcohol, cigarettes, sugar, fatty fast food is something we should worry about. Its time to chill and let people enjoy what they love.
Amen!!! Worry about the real problem-prescription drugs, meth, etc.
How something disconnecting your brain could be good for you!? I don't believe you're not a smoker for saying this. Haven't met that one sober person with fully functioning brain who would say this...
Hell no Lola. I will not just agree to let folks do what they want when it comes to smoking. If you have a 15 yr old son who is not doing well academically and has started to hang out with those who have no job and smoke weed in cars, Hell no i'm not just going to say.....ok 15 yr old do whatever you want to do because you love it. That's not how this parents thinks or how this household is run.
Of course not. So maybe make sure he's not struggling... pot helps ease mental pain... those who have a mental illness turn to it to help ease anxiety, stress and worry. He needs your doting love even though it doesn't seem like it. Instead of going on an angry power trip.... talk to him ask him why he does it, let him know the facts and that if he does choose to smoke later on life then he can do that. But not while his brain is developing as it does worsen mental illnesses. Anger isn't the answer
Ugh. I'm dealing with this right now. My neighbors have been smoking pot pretty much all day, and I was trying to do my Algebra review for a test, and I have a massive headache now. My apartment also smells like a skunk lives in my closet too..
Skunk smells very differently from weed! I love the smell of certain weed, but I don't smoke as I don't like the affect it has on me; I use salves and lotions derived from weed for my ailments throughout my body and it helps immensely!
People who don't smoke weed think it smells bad because it does. We only think it smells good because we have connected that smell to the pleasure center in our brain. We've associated weed smell with getting high, but other people haven't. Be respectful and try and keep your weed smell off of everything.
um no. i know tons of non smokers that like the smell. Like how some people like the smell of gasoline, or sharpie. I agree, be respectful, but don't generalize and say we only think we smell good because of association when that's absolute bull.
You do not know people who don’t smoke that like the smell. You”re either lying or misremembering. If they like it and don’t currently smoke they probably used to smoke but don’t anymore because they finally got a job. I suppose there’s also the possibility that since you always smell like pot they may have lied to you to spare your feelings.


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