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.


i smoke on the daily and have a gap of 96.. I'm in advanced classes and often times marijuana helps me in my studies. i do hate with a strong passion alcohol and cigarettes. can you please tell me how many deaths are caused by marijuana?

It is very unlikely for a person to overdose and die from marijuana use. However, people can and do injure themselves and die because of marijuana's effects on judgment, perception, and coordination, for example, when driving under the influence of the drug. Also, people can experience extreme anxiety (panic attacks) or psychotic reactions (where they lose touch with reality and may become paranoid). (https://teens.drugabuse.gov/drug-facts/marijuana)

I agree. I cheef daily
Some people have good job
Typical selfish dumb comment weed when smoked stinks and offends others that don't smoke weed
Some people (not a dorm situation ) have to worry about DOT drug rests
It makes my stomach turn. Worse than cigarette smell.
If one is not a smoker of anything, one's sense of smell tends to be more acute.
It stinks and if you are 13 like me you dont want to smell that.
It's not just the smell it's the affects it has me the damage it can do
The smell is disgusting, even worse than cigarette smoke. I don't like it.
I agree. One has to smell to understand. I don't even smoke cigarettes. People in downstairs apartment smoke weed all day. It smells horrible in my apartment.
Duh? Because it doesn't smell great?
Because they do....go outside and smoke.
You're a snitch lol
Kids duh. They don't choose to smoke. It affects their brains. You should now
You should know* not now. Just an FYI. You need to save every brain cell you have
Omg your wasting tax payers money and wasting police time, cause of a smell... to be fair earth made the weed plant and cause we decide its harmfull you think it is. Whys is booze man made but not against the law but it cause more harm then cannabis dose. Infact they proven it to medically help you. Its from the earth its self not man made. I dont get this world.
Weed today is not natural. You think Marijuana naturally has 15% or more THC? And besides, something being natural means very little. Cobra venom is natural, that must mean it's not bad for you. At any rate though, marijuana has not been shown to cause any negative effects outside of smoke inhalation damage to the lungs, and diminished brain development in individuals under the age of 25. And you can remove the first one if you vape THC instead.
Great comment! I m sick of smell of neighbours weed and do worry it effects my grandkids..why should i have to close all my windows on hot days
So are you going to come to my house and shove a vitamen down my throat because its "good for me." Everyones missing the main point here, NO ONE has a right to force someone to smoke secondhand marajuana smoke. And yes just because its not getting people high does not mean that the 1. psychoactive substance THC and 2. any other substances and pesticides in the marajuana smoke are not entering their bodies. What gives anyone the right to force me to put a psychoactive drug in my body that I don't like. I don't care how "good" you think it is for me.
I am around 50.. I agree with those who is against the smell and possibly the effects- not all people react the same to medication, for those that are stating it is medicine - I am prescribed medication for pain if my blood, cheeks, or urine showed up positive :I would be screwed. I am asthmatic now and I never smoked a cigarette. As a teenager, I tried smoking pot; but, I had an adverse reaction. Later, to find that I am schizoid affective. Not everyone is the same ,if we were we wouldn't need a variety of meds. Instead of thinking just about you- you may consider the person next to you.
Thank you Linda for posting this as its relevance includes people of all ages! I actually had the same situation occur to me. Bc my neighbors smoke weed in the apartment next door (and they have parties each night and despite closing my windows I can still smell their smoke and the apt is always so full of smoke like the cloud is so dense you can't even see through it!) and so at my pain management drs office not too long ago they did the usual routine blood work and urine tests and they found evidence of pot use. I was so confused bc since I have asthma I have never smoked a cigarette or pot even once (I go into anaphylaxis) Bc it may be legal in some states doesn't mean there aren't still people who are banned from having contact with pot, like individuals with chronic pain who are on pain contracts with their Drs and basically almost all of them state that if pot is found in your urine you can be spontaneously kicked out of the clinic therefore causing a great deal of pain and stress to another person. Thankfully my doc was understanding about my neighbors abnormal behavior but it scared me to death! I think it boils down to where you use pot that is if it's even legal in your state. I mean if you have close neighbors like in an apartment building generally a person wouldn't turn their tv up all the way just bc they prefer it loud. Because they live in a close quarters community, they have to consider the lives of their neighbors just as their neighbors do as well- it's called being an adult. Where as if someone who owns a farm likes to smoke pot occasionally and their nearest neighbor is a few miles away I feel that there is a difference in that situation bc what they are doing won't affect their neighbors (assuming the individual lives alone). Plus scientific studies have proven that both Tobacco and pot smoke is bad for dogs and cats, so if you don't care about neighbors at least consider your pets and their well being! I find it so incredibly concerning that some people are so self centered that they don't even care about how something they do might affect their neighbor! What's happened to getting to know your neighbors? So sad.
Yes I deal with this all day my boss, dad, mom, sister, friends everywhere I go I'm around it and I don't like it but I can't tell my boss to stop or I'll be fired and ect with family
right ! i swear people just tend to overreact to such dumb stuff it's completely idiotic to me in my opinion !
need the Conservatives back in power to criminalize any use of cannibis and jail peopl who use it near children and others.
I live with a cannabis smoker and it really affects my breathing. Our bodies weren't made to smoke so smoking cannabis is not natural. Also. Dung is also earth made but I wouldn't spread the smell of it around my house
Your kids are gonna smoke it anyway
Dude savage
I tested positive for marijuana and I do not smoke. I was in total shock! My neighbor smokes it but I have never been in the presence when they were and never stuck around when I could smell it, because it's gross.. I don't know if there is such thing as a defective drug test or if I could actually affect me like that..
Unfortunately I live in Colorado! My daughter who is a child with Down Syndrome and a congenital heart defect is being effected poorly from our neighbors below. It literally smells as if I have been smoking it in my own apartment sometimes. They live below us, so the smoke travels up. Both my daughter and I get headaches and stomachaches from the smell. However, my daughter has a lot of ear, nose and throat problems and it makes her eyes water and her nose run a lot. I keep cleaning and it doesn't help! Though the neighbors below have complained about the noise I make cleaning all of the time. They must smoke in their room,because the odor is strongest on my daughters bedroom. She can't sleep because of how it effects her. This is just awful, and there is nothing I can do about it in this state.
Run to the cops snitch you act like people doing herion or something
Don't matter some people got jobs they could lose if I'm going to lose a job I would rather lose it for something I did. Not from the help of my neighbors for something I don't even do. I social drug use is for the weak minded someone who can't face life sober.
Not in England been fighting 3 years still no luck
I agree. I think the smoked form should always be illegal. If people were drinking it in tea or eating it nobody would care. But they're hurting me and my family by putting it in the air.
The problem is that some of the states that have made it legal for medical use have limited the way it can be consumed. For example in Pennsylvania it can only be taken in oil form. So smoke or vaporizer. Vaporizers cost $250-$400. Smoking is about $20 maximum. So y'all can start talking to the building owners to find out why your apartments and condos aren't better insulated. And why you weren't complaining about the smell of regular tobacco or even the smoke from crack or even a fireplace.
what asnitch. its called knocking on your neighbors door and telling them the problem.
You will have a person locked up for taking their medication? Because research shows that people with glaucoma need the drug. I'm asking for a friend.

NIDA is a public health agency and does scientific research; we do not make laws. Different states have different laws about medical marijuana, so you can check what's going on in your state. Because you mentioned glaucoma, you might be interested to know that the National Eye Institute (NEI) has done research showing that current medications are more effective than marijuana for glaucoma. You can read the NEI report here: https://nei.nih.gov/news/statements/marij
There's a lot of research going on related to other possible therapeutic uses of marijuana and its constituents. For more information, see https://teens.drugabuse.gov/drug-facts/marijuana

The fact the you are using the words "not likely" and "not normally" in this article it is very clear that you ar defending marihuana and being very bias instead of just providing facts about the subject
i agree with baker if you would experience effect of 2nd hand cannabis smoke like some people are - me included you would look at it differently.
I was a cdl holder until a few days ago when i tested marijuana.the dot has an exceptable level of thc in urine at 15 nano grams per milliliter thats 15 billionths of a gram per millionths of a liter volume by weight.i was in a parking lot and smelled weed in the air the next day my sister inlaw sparked up near me about six feet away.i moved away into the garage where i unknowingly walked into where she had just been smoking.took a test two days later and tested positive for thc well above 50ng per mL
I do not smoke weed & I'm on probation & I could get sent to jail if I smoke so heck no I don't, I went for a job & had to take a drug test & I nearly failed, by some miracle the line I mean barley showed color, put it this way the Lady must have either been a pit smoker or was just in a good mood that day, I sat in smoke daily I never would dream this could happen!
Mickey moose you are obviously lying. If you arent a habitual user the thc from directly smoking pot will ne out m of your system in ad little as 12 hours.
That's because you smoked, silly. There's no way you tested that high for not actually smoking. Second hand smoke won't peek levels above 5 nano-grams, and that's if you're sitting right beside a pot smoker. Just admit to everyone on this forum thst you actually smoke and lost your job because of your own actions. Feeding untruth across the Internet is a political tactic to control the masses. Are you being paid to spread this false statement? Please be honest.
A mililiter is 1/1000 of a liter
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.


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