Short answer
Yes, secondhand marijuana smoke can get a nonsmoker high, but only under specific conditions: heavy smoke, a small space, no airflow, and a high-THC product. Outdoors or in a ventilated room, the dose is small. Most nonsmokers feel nothing. THC metabolites can still appear in urine.
What is in secondhand cannabis smoke
Burning cannabis releases THC, CBD, tar, carbon monoxide, and fine particles. Sidestream smoke from the lit end of a joint carries THC and combustion byproducts that a bystander inhales. Potency matters. Federal potency monitoring found average THC in tested flower rose from under 4 percent in 1995 to about 15 percent by 2017. A room filled with smoke from 20 percent THC flower delivers more THC to a bystander than the same room did in 1990.
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What the studies found
Cone and colleagues published controlled exposure studies in 2015. Nonsmokers sat in a van or a room with smokers using 11.3 percent THC cannabis. In unventilated conditions, nonsmokers had detectable THC in blood plasma, a small rise in heart rate, and low scores on self-rated high and stoned scales. Cognitive and motor test scores shifted on some measures. In ventilated conditions, blood THC was low or undetectable and subjective effects were minimal.
can secondhand thc smoke cause a failed drug test
Urine testing in the same series found carboxy-THC above the 15 ng/mL confirmation cutoff in some nonsmokers after unventilated exposure. Ventilated exposure stayed below that level.
passive weed smoke and children risks
Dose depends on the room
- Space size. A car with windows up concentrates smoke. A living room with a window open dilutes it.
- Airflow. Fans, open windows, and exhaust move smoke out before it reaches a bystander.
- Number of smokers. More burning material means more sidestream smoke.
- Time. Thirty minutes in a closed car delivers more than a passing breath on a sidewalk.
- Potency. Higher THC flower raises the airborne dose.
Will a drug test catch it?
Workplace urine screens use a 50 ng/mL immunoassay cutoff. Secondhand exposure in a ventilated space stays below that. Unventilated, heavy exposure can push a sample past the 15 ng/mL confirmation cutoff, which a lab reports as positive. Blood THC from secondhand smoke clears within hours. Urine carboxy-THC can remain detectable for days after heavy exposure.
Children and other high-risk groups
Children, infants, pregnant people, and people with asthma or heart disease face the largest risk. Secondhand smoke of any kind raises the rate of respiratory infections, ear infections, and asthma attacks in children. THC exposure adds a psychoactive compound to that mix. Pets in a closed room with smokers inhale the same particles.
How to cut exposure
Smoke outside. Keep car windows down or smoke alone. Use a fan and an open window if smoking indoors. Air purifiers with HEPA and carbon filters cut particles and some gases, but no filter removes all THC from a room.
What is not known
There is no standard dose-response model for secondhand cannabis smoke. Study samples were small, with six nonsmokers per exposure session. The THC dose that triggers a subjective high in a bystander is not established. Results vary with body weight, tolerance, breathing rate, and room conditions.