Drugs & Health Blog

Secondhand Marijuana Smoke?

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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.


I leave in California, where a patient can plant up to certain amount of marijuana plants in their backyard. This is the story.The person who has the medical marijuana identification card (MMID)don't smoke marijuana at all,but her husband with some other friends use her MMID to plant Marijuana and sell for profit.There are lot of doctors that will approve you for MMID,even though if you don't need MMID, just pay the doctors some money, and you get it.I don't smoke marijuana at all,but there are people who smoke,and really strong smell.I can't take that smell and so does other neighbors who don't smoke marijuana at all.To avoid the smell,I have to stay indoors.I feel like the freedom to breathe fresh air is gone.It also gives me headaches and I get allergies.
I do smoke weed. I have been asked by roommates and visitors to take it outside. Smokers have to understand that not everyone is going to like it. It's just courteous to ask if it's "Ok I smoke?" Plus going for a walk and smoking a J is awesome. Being a pothead I can certainly say that it has affected my memory but at the same time it gives me a stronger creative outlet for writing and drawing. When I got high at work my performance was definitely not as good so I stopped getting high at work. It's like alcohol in that sense.......just save it for your free time and take it outside like a cigarette and everyone is happy.
This is absolutely NOT true!!! The smoke will affect you and give you a high different than inhaling it.
So my question is; if someone takes a hit off of a Marijuana joint and I mouth to mouth inhale their exhale; will I test positive in a hair follicle??

Hi Sha, we haven't seen research studies yet that answer this question.

Can weed get in your system if you blow someone a charger. Then 2 weeks you go for 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.

How about this? Your ex wifes boyfriend exposes your young kids to it daily. They also know that he smokes Marijuana and is at a very impressionable age. Hes been told theres nothing wrong with it by his mother. How do you teach your kids to stay away from it when it's right under their noses? So frustrating. I've seen kids through away their education over it. So scary.
How about this? Your ex wifes boyfriend exposes your young kids to it daily. They also know that he smokes Marijuana and are at a very impressionable age. They've been told theres nothing wrong with it by their mother. How do you teach your kids to stay away from it when it's right under their noses? So frustrating. I've seen kids through away their education over it. So scary.
God said in the Bible He would judge those who didn't give up drugs. Welcome to Hell.
i leave with a weed smoker ,l ve never smoked but am always feeling tired,sleep too much like him and always angry.i hate it
I too can't stand the smell, used to come into my bedroom which I share with my disabled brother. And it kept coming in my window every night after 11pm cos my neighbor was smoking it a couple of metres from outside my house. It really don't phase me if people want to smoke it as long as you don't do it in front of children and they don't breathe in that secondhand smoke. The old saying ''Each to their own'' I suppose. Just have respect for your neighbors who don't smoke it. So if your in a situation like me, don't be grassing to the police unless you really have to like if they're being violent or something but just politely ask them to move of your property and smoke somewhere else.
Man I was shooting a music video and they had a blunt of loud in rotation and I got high just being in the room! Although I love the smell I hate the feeling!
It is very commonly misconceived that secondhand marijuana smoke is harmful, and people need to spread awareness.
I do not smoke marijuana. Never have. Through unfortunate events three of my four children did find it. I get horrible migraines, very anxious, and suicidal from the stuff in the air in house even if I don't smell it.
My brother smokes weed I don't but I have a cold and I was wondering if it could make my sickness worse

Hi Carley, smoke from marijuana can irritate your lungs, so if you have a cough, it's possible it could irritate your lungs further.

Im scared of failing my drug test because of second hand smoking

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.

I walked into a school bathroom and there was someone smoking weed, I was in there for a minute and it wasn't well ventilated, will this have any affects on me long/short term.

Here's what we know about inhaling secondhand marijuana smoke:
• If you inhale secondhand marijuana smoke, it's unlikely you would fail a drug test, but it is possible.
• Secondhand marijuana smoke is more likely to give someone a high if they're in an enclosed space with others smoking marijuana with high THC levels.
• More research is needed, but we do know that marijuana smoke can especially affect children and people with asthma.

For more information, please visit https://www.drugabuse.gov/publications/marijuana/what-are-effects-second...

I live in senior subsidized housing in Indianapolis. I already had respiratory problems when we moved in here 7+ yrs ago. Now, I have asthma. Also, I am now showing high blood pressure, dangerously high. I have a new neighbor the past few months I can't lay down and sleep in my own bedroom. I cough and vough so hard it feels like my lungs are going to come up. I get a headache. I feel weak and sick half of the time. This is NOT a normal progression. The management of this bldg turn a blind eye to all of the drug use. We've had three sets of mgrs, all the same. The police will not come and would do nothing if they did. I'm not rich and moving is something I'd have to save for months to do. IF another bldg would rent to me knowing where I live now. This is a HUD subsidized property and one of HUDS biggest no-nos is " NO DRUG USE IN THEIR PROPERTIES." Yeah, right
Half of my school smells like weed or smokes it. It's disgusting since I'm sensitive to the smell
So my neighbors up stairs smoke like there is no tomorrow and every time the smell penatrates down to my apartment I have a two year old boy and I have grown concerned can my child be exposed to 2nd hand smoke by this point? Can it affect him. The smell is strong sometimes his Allergies start to act up. Any advice?

You would be surprised how often we get this question. Many people in apartments complain about marijuana smoking in other apartments. If possible, keep your apartment well ventilated, with lots of fresh air. We cannot assess your son’s personal health situation, but you should speak to your boy’s pediatrician about it. You can also discuss this with your landlord; he/she might be willing to let you move to a different apartment, especially if you can get a note from your son’s doctor.
You have not said if you come from a state that has legalized marijuana. If so, your state should have a website that explains how the laws work in your state. There might also be a phone number or e-mail you can contact and see what your rights are. We are sorry you have to experience this. In the long run, you should consider moving if at all possible.

I have to take a hair follicle and urine test this Wednesday. But sept 8th I was exposed to second hand marijuana smoke I was in a house and to my knowledge they smoked one joint. Will that cause me to fail the test

It’s not likely that you will fail a drug test due to secondhand marijuana smoke exposure. However, 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.

Can one test positive for weed if they smoked a cigarette from a pack that a turned off joint was stashed in?

Probably not.


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