No, you can't get high from smelling cannabis. The smell is made of aroma compounds, not THC, and a whiff in a hallway or at a concert delivers nothing. A contact high is a different thing: breathing in a lot of someone else's smoke in a closed space.
Researchers tested that directly. Non-smokers shut in a small, unventilated room with heavy smoking for an hour absorbed measurable THC and felt mildly sedated. With the room ventilated, they absorbed far less and reported no drug effect. Secondhand smoke still isn't harmless: the CDC says it carries many of the same toxic chemicals as tobacco smoke and can pass THC to children.
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What is a contact high?
A contact high is feeling the effects of cannabis without smoking it yourself, by breathing in smoke from people around you. The phrase is also used loosely for feeling giddy because everyone else is high, which is mood, not THC. For the real thing, you need to inhale enough smoke to absorb THC, and that takes more than a smell.
Smelling weed vs. breathing smoke
The smell of cannabis comes from terpenes and sulfur compounds, the same families of molecules that make pine, citrus and skunk spray smell the way they do. They float off fresh flower and burning flower alike, and they have no THC in them. You can smell a dispensary from the parking lot and nothing happens. THC rides in the smoke itself, in tiny particles, and only reaches your blood if you breathe that smoke in. The weed smell page covers the chemistry.
What the studies found
A team at Johns Hopkins ran the experiment most people imagine. In 2015 they put six non-smokers in a small sealed room for an hour with six people smoking cannabis the researchers called high potency (11.3% THC), with the ventilation off. Then they repeated it with ventilation on, at a rate the authors compared to a home heating or air conditioning system.
- Sealed, no ventilation: the non-smokers had detectable THC in their blood and urine, slightly faster heart rates, "mild to moderate" sedative effects they could feel, and more mistakes on a simple speed-and-memory test. A real, if modest, contact high.
- Same room, ventilated: much lower blood levels, no sedative effects, no drop in performance.
The authors described the sealed condition as extreme: a room about 10 by 13 feet, the size of a small bedroom, six people smoking for an hour, no airflow. A car with the windows up and several people smoking is the closest everyday version. A living room with a window open, a patio, a concert, or a friend's joint on a walk weren't tested, but they are much closer to the ventilated room than the sealed one. If you can't see smoke hanging in the air, a contact high is very unlikely.
What a contact high feels like and how long it lasts
Mild. The non-smokers in the sealed room reported a mild drug effect and felt more tired and less alert, well short of what the smokers felt. Those effects were gone within about an hour and a half. Inhaled cannabis is felt within minutes, so if you were going to feel something from a smoky room, you'd feel it there, not an hour after you left. If you feel strongly high after being around smoke, you may have inhaled a lot of it, be very sensitive, or have taken something else. The too high page has what helps.
Is secondhand weed smoke harmful?
The smoke matters more than the high
The CDC says secondhand cannabis smoke contains many of the same toxic and cancer-causing chemicals as tobacco smoke, some in higher amounts, that THC can be passed to infants and children through it, and that people exposed can feel high. The contact-high question is mostly a curiosity for adults. For a baby in the back seat or a kid in the apartment, it's an exposure. Smoke outside, away from windows and doors, and never in a car with children in it.
Can dogs and cats get a contact high?
Yes. Veterinary poison experts say breathing in cannabis smoke can poison a pet, and that there is no safe dose of THC for them. The ASPCA lists marijuana as toxic to dogs and cats, with signs including prolonged depression, vomiting, incoordination, drooling, dilated pupils, low body temperature and, in severe cases, seizures or coma. Eating flower, edibles or ash is the usual route, but smoke in a small space counts. Keep pets out of the room, keep products locked away, and call a vet or an animal poison line if a pet seems off after exposure.
How to avoid a contact high
- If you're the non-smoker: move air. Open a window, step outside, don't sit in a closed car with smokers. Ventilation was the whole difference in the study.
- If you're the smoker: take it outside, or at least to an open window, when anyone who didn't choose to be high is around. That includes roommates, kids and pets.
- Vapes and edibles produce little or no secondhand smoke. See vapes and edibles.
We don't cover drug testing on this site. If that's your worry, the honest answer is that it depends on the test, the exposure and the timing, and a lab or your employer's policy is the place to ask.
Words you'll hear
- Contact high, secondhand high: effects from breathing other people's smoke.
- Hotbox: smoking in a sealed space, usually a car, on purpose. The study's "unventilated" condition, in slang.
- Terpenes: the smell. No THC.
- Sidestream smoke: smoke from the burning end, as opposed to what the smoker exhales. Both count as secondhand.
Common questions
Is a contact high real?
Yes, under extreme conditions. In a 2015 Johns Hopkins study, non-smokers shut in a small unventilated room with an hour of heavy smoking absorbed THC and felt mildly sedated. With ventilation, they reported no drug effect. A whiff of smoke outdoors or at a party doesn't do it.
Can you get high from smelling weed?
No. The smell is terpenes and sulfur compounds, which carry no THC. Only inhaling the smoke itself, in quantity and in a closed space, can produce any effect.
How long does a contact high last?
It's mild and short. In the study, the effects were gone within about an hour and a half. Inhaled cannabis is felt within minutes, so if you didn't feel anything in the smoky room, you won't feel it later.
Can you get secondhand smoke from weed?
Yes, and that's the real concern. The CDC says secondhand cannabis smoke carries many of the same toxic and cancer-causing chemicals as tobacco smoke, some in higher amounts, and can pass THC to infants and children. Smoke outside, away from windows.
Can dogs get a contact high?
Dogs and cats are very sensitive to THC, and the ASPCA lists marijuana as toxic to them. Breathing smoke in a closed room can poison them, and so can eating flower, edibles or ash. Keep pets out of the room and call a vet if a pet seems wobbly, sleepy or sick.
Can you get a contact high in a car?
A closed car with several people smoking is the everyday version of the study's sealed room, so yes, a non-smoker can likely absorb some THC and feel mildly sedated. Windows down changes that. Never with children in the car, and nobody drives after.
We cite government health agencies and peer-reviewed research. Numbers in the text link to the source.
- Peer-reviewed Herrmann et al. (2015): Non-smoker exposure to secondhand cannabis smoke II, effect of room ventilation, Drug and Alcohol Dependence
- Government CDC: Secondhand cannabis smoke
- Government Health Canada: Health effects of cannabis (inhaled effects within minutes)
- ASPCA Animal Poison Control: Marijuana is toxic to dogs and cats
- Peer-reviewed Oswald et al. (2021): Volatile sulfur compounds and the smell of cannabis, ACS Omega
- Pet Poison Helpline: Marijuana (smoke inhalation can poison pets)
