Facts About Second-Hand Marijuana Smoke

People who don’t smoke marijuana, but hang out with those who do, may have some questions about the effects of second-hand marijuana smoke. For instance, they may want to know if they can get a contact high by just breathing in the smoke from other people’s joints. While there is minimal research on this topic, there are some facts about second-hand marijuana smoke that you should know.

Mild Contact Highs Are Possible

Research shows that you can get a contact high just by being around marijuana smoke, but only under very specific conditions. First, you’d have to be in a small, unventilated room, and second, you’d have to be around the smoke for a very long time. Even then, the most you’ll feel is a little buzzed or hazy, and you might not perform as well on tasks that require significant mental focus. Additionally, you’ll return to normal almost as soon as you start breathing fresh air.

If you’re around people who are smoking marijuana and you’re in a large or ventilated room, you don’t have to worry about getting high at all. A study that examined people in this setting who were around smokers but didn’t smoke themselves showed no change in their physical measurements (like heart rate and blood pressure) after being exposed to the smoke.

Positive Drug Tests Are Possible

Despite the relatively low risk of getting high by breathing in second-hand marijuana smoke, the risk of testing positive on a drug test is more concerning. This is specifically a risk if you’re in an unventilated room with someone else who is smoking marijuana, but you can’t rule out the possibility that you’ll test positive even if you’re in a well-ventilated room. This is because drug tests detect THC levels in blood, saliva, and hair, all of which can return a positive result if you’re tested soon enough after exposure.

Heart Damage is Possible

This is one area where studies on second-hand marijuana haven’t caught up to those on second-hand cigarette smoke, but in the limited research available, there is some indication that second-hand marijuana can cause more damage to the heart than cigarette smoke. Both marijuana and tobacco cigarettes contain similar chemicals, so this result is no surprise, but it’s not a foregone conclusion. Still, it’s always better safe than sorry, so with the lack of benefits of second-hand marijuana smoke, you may just want to avoid it altogether.

Allergies are Exacerbated

This is another fact about marijuana smoke that’s no surprise, but you may not have considered it before. If you have allergies, both cigarette and second-hand marijuana smoke can make your condition worse. In fact, exposure to cigarette smoke can actually cause children to develop new allergies, particularly to foods. For this reason, kids should always avoid places where there is smoke, whether it’s from tobacco or marijuana. If you suffer from allergies that affect your respiratory system, you should probably stay away from both as well.


Since there’s almost no chance of catching a contact high from second-hand marijuana smoke, there’s really no reason at all to place yourself in a situation where you’re breathing it. The risks of testing positive for the drug, damaging your heart, and experiencing allergies are simply not worth it.

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