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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.


Same exact thing happened to me a few days ago. My step-son smokes and I walked into the garage and nearly fainted. Good thing i'm only on probation and nights for like six months.... Kept my CDL and Job.
the fact that your attacking the article that clearly states "MARIJUANA HAS NOT EVER BEEN LINKED TO HEALTH PROBLEMS IN HUMANS" air quotes don't lie. claiming the person is being bias is just you trying to belittle some one because of your own shortcomings about the topic. if you dislike the article, write your own, but i doubt yours will pop up as the top 5 sites for this search. I dealt with acid reflux since i was 12, it would get soo bad i'd suffer for hours at times due to the pain it caused in my stomach as if i had food poisoning, without the vomiting or other end of it, I tried marijuana when i was 24, and am a Legal user, i smoke each evening, but if i had to i could go a few days at a time before the beneficial effects ware off, Yes for a short time before bed i do feel high, but the following day I wish i was the kid who hung out behind the bleachers because i would have been able to be a normal not-in-pain kid and teen. Go ahead, call me bias because i do use it, do i abuse it? nope, but i do live a much easier life thanks to it. IF some one was bias, they would slander the tobacco industry, this person is stating known facts, not his/her problem if you can't read it correctly for what it is.
I read your post. Granted this is a year late. I also have severe acid reflux, ever since I was a little kid. It is so bad that I have choked several times in my sleep and woke up choking. My throat feels like it is on fire and the taste would not go away and I have to stay up for several hours in the middle of the night until I can safely go back to sleep. Also I do not know why you smoke weed to solve the problem. If it is because of the pain then it is not acid reflux. Acid reflux is something that is caused from a combination of different things. Such as the position of your body and what you eat as well as the activity you are performing. To have constant pain does not constitute Acid Reflux. You either have an issue in your stomach lining or ulcers. So with that said I do not know why you were given medical marijuana when that will not do anything for acid reflux. Any sensible doctor would have prescribed you Omeperazole. This is a medication that helps greatly with acid reflux. He would have also suggested a change in diet as well as different sleeping positions. So with that said you are mistaking it, or are lying about the whole situation. Since I actually have acid reflux, this is very offensive and I wish you would not use the disease as an excuse to smoke weed. Again I would consult a specialist as I have and find out what is causing your constant pain in your stomach. Because somewhere along the line either the medication or you are doing something very wrong to keep causing this pain you are experiencing. Also I have every right to be biased when it comes to making sure people don't have to be exposed to inhaling others' smoke from marijuana use. Do you know why? It is because of the medication that I am on as well as my conditions. So even a chance of second hand smoke can cause very negative and unknown side effect in my health. I suffer from Tourette Syndrome, ADHD, OCD, Depression, Anxiety and am on a various assortment of medication due to all of these medical conditions. Also keep in mind not just the effects of my conditions and the medication, but the side effects of the medication as well. So when I am exposed to second hand smoke, I do not complain just because it smells bad. People should be more respectful of others and do not know what smoking a medication near someone else can do to their health. Also I am very aware of the medical effects of Marijuana and the dosage it take to actually have an affect of the human body. So don't think that a little bit isn't going to affect someone. Also this article is absolutely ridiculous. I have yet to see a medical or scientific fact stated. This is basically a blog for someone to defend weed. Marijuana has side effects that are not all that good. And a lot of people smoke it and abuse the law just so that they can get high. You need to see where people who do not smoke are coming from. Be more respectful and realize things for what they really are. Thank you for reading this comment and I hope you are able to get a better diagnosis for whatever ails you. Have a wonderful day NinjaGrowPwnz
What about if you had a friend you visited 2 - 3 days a week over a period of 2 yrs in a small room unventilated. I don't smoke it but my drug test came back positive - I got fired!
Dude, do you not understand why second hand smoke in an unventilated room is not the same is in a well ventilated area or outdoors? You may as well be smoking it yourself if you're in an unventilated room. The only difference is that you're not getting as much THC as quickly the person smoking it, but you're still going to take in like 25~50% of whatever they get.
I was on the beach with friends just yesterday and we were outdoors and they were smoking pot and they smoked three puffs in front of me and then went away do you still think I could fail a drug test

It's unlikely.

That really sucks! Leave when they smoke!
My 3 year old has to take a hair drug test ; she has been exposed to second weed smoke offenot from her father . He lies and says he doesn't do it around but ik him and how he is so he thinks second hand doesn't affect. But any way the point to my question is . When she goes to take it will it show up in her system if she does not smoke it her self just been around it

May we suggest you contact the Government’s National Helpline. It started as a suicide prevention helpline but now counselors are available 24-7 to discuss any issues of concern, including the kind of question you've asked.

So what? The 3 year old is going to be in the years when marijuana will be legalised and realised for its medicinal and recreational abilities. There are thousands of cancer patients who are able to enjoy there last moments in life without being in constant pain.
Just because they use the words not likely and not normally does not mean that they are bias. These are the facts that they can provide, what else do you want?
Did you ever here of doing a shot gun to some one, yep its second hand smoke an yep you get high an yep you fail drug test any body that never smoke pot should not have a opinion on matter they do not know what what they are talking about. smoke one an you will know, untill then shut up
You are getting more THC that wY. .in a room with just 1 person smoking or you smell!!! You cannot get high or fail a drug test. I give drug test everyday.
So I might see a buddy once a week maybe? He might hit his piece 4 times while im around, never blows it in my direction. We are in a large well ventilated room. Will that show up in a hair screening?

Probably not.

I haven't smoke weed since June 14 2015 my brothers smoke loud weed. I tested negative Monday n Wednesday comes n I drop positive for thc they smoke outside I smell it sometimes. So y u think I fail da drug test today?
Could I fail a drug test if I took my meds that were kept in the same area as loud weed?

Probably not.

Loud weed?! Lmao wtf is that? Please call it headies or at least exotic ( which is also a term used incorrectly all the time). If it's not from somewhere in the continental USA it's safe to say it is exotic. Otherwise, it's just HEADIES. ( not an actual strain name)
You obviously don't get out a lot. Everyone says they have loud weed. Its another way to say its good weed and smells up a whole room, like a person screaming in a room, LOUD!
I have a hair follicle test soon and I've been around my dad who smoked it. It's been about a month since that. Could I fail it? Do I need to tell them?

It's not likely that secondhand exposure would show up in a drug test. However, if you want to talk with your family about drug use, you might check out some of the resources on this page:

We use to smoke always outside never in house or vehicle but our roommate who doesn't smoke failed a Ua he's never around when we smoke why did he fail? Is it because of it from our clothes or household objects we touched after smoking ?

It's not likely your roommate could inhale enough secondhand smoke to fail a drug test.

Can someone fail a hair test if there in the same house as someone smoke running a round

The Substance Abuse and Mental Health Services Administration (SAMHSA) is the federal agency that addresses drug testing guidelines. Though your question is not related to workplace testing, you should contact the following: Drug-Free Workplace Helpline: 800-967-5752 (800-WORKPLACE) HELPLINE@SAMHSA.HHS.GOV

well as for a shot gun the whole point is giving the other person a hit.. whichh your not supposed to inhale the hit. If you inhale you are getting the thc molecules. Not inhaling would be giving them the thc molecules which would get you a failed test.
I know this is an old article but i go to a methadone clinic and have been for 2 years, i was addicted to oxys after 2 surgeries when i was 18 and 21 never was a pot smoker or any other illegal drugs or prescription pills. I've been clean of oxys since i started at my clinic well after 2 years of clean urine drug testing i get a oral swab, no big deal I'm clean. .. nope i went in yesterday and was told i tested positive for marijuana! I'm 32 years old and the last time i tried it was when i was 15! My husband of 12 years smokes it daily and I've always been around him n never smoked or failed a drug screening note all of a sudden i test positive for it and lost my 2 week take homes of methadone that i really did earn. I told them theres no way i do not smoke! Is there any way to argue this as being second hand or from sexual Intercourse/oral or just kissing? I contested it but he told me to hold off til he can find out the exact levels then I'll be given another test. I told him i wanted an oral and urine and blood
"We also know marijuana contains harmful cancerous chemicles like cigarettes." At this point stupidity has taken over humanity lmao, it is IMPOSSIBLE to die from cannabis, weed, marijuana (all same thing)
research indicates that it is not a benign substance.. I.e., smokoung weed comes with detrimental health effects. Common sense also tells us that smoke (of any type) is not healthy. Thus, to claim that smoking weed is completely without risk is seriously ignorant.
I don't know! I looked this up because my neighbors keep smoking and it goes into my room. I keep waking up from the smell and I'm scared of what it's doing to me :(
I was sitting on the grass at the park. And my brother said, "what's that smell?". When I turned around I saw an old lady smoking weed. We left as soon as possible!
Bull you can get high of marijuana and if someone blows it in your face you can get stone you must be a smoker a smoker also wouldn't know if a person can get stone because they smoke. If you have and allergies it can also have an affect on the brain even trimming can make u feel as if your stone maybe they should test freakin people that don't smoke n people that do this is bull
I failed a test and I didn't even smoke just cuz I was around marijuana smokers..
Amen, & don't look back. I have no choice as I live in section 811 housing & there is no other place around here
I had muffins with quit abit of poppy seeds on it& had a drug test& it came up positive. also could second hand smoke of Marijuana come up positive on those kind of tests?

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

On a related note, you should check out our post Drug Testing for ...  Poppy Seeds? which talks about how poppy seeds can cause you to test positive for opiates.

Your not counting the smoke coming off the joint while its just burning, this has more effect than what is exhaled, it is unfiltered ...
Right. That worries me, the smoke coming of the burning blunt in the front seat of a new car.
That's totally untrue ... just today I failed a drug test for thc when I don't even smoke it and was only around my husband using very little!
I have failed two drug tests due to little inhalation if any.
I have failed one also and I was only at my neighbors house for a minute and they were not smoking at the time but you could smell that they had.
Actually you can fail a drug test because my sis in law fail two already due to her brother smoking in the same room n she doesn't smoke second hand smoke.
I visited Amsterdam last were and there were many people smoking marijuana. My nieces hated the smell and were desperately trying to cover their noses from inhaling the smoke every time we pass by a marijuana user. Please, stop using marijuana and we can make the world a better place.
You're foolish. You don't like the smoke from it? Fine, I don't like the smell either, but MJ does actually help people. If you've ever seen a child have tremors and watch them subside from MJ and still think it should be banned, you're a cold hearted person. It does have some legitimate uses..
I don't smoke weed, for a few years now but my fathers older friend has been smoking it for over 60 years "daily"and he just celebrated his 91 birthday and he is healthier than most 50+ year old ppl we know. So I'm all for it, if it's what u want to do.
why go to Amsterdam of you don't like weednotsnthe bloody weed capital!!!!!!
Poppy seed is crack


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