Secondhand cannabis smoke can cause mild intoxication, eye and airway irritation, and short-term changes in heart and blood vessel function, especially in enclosed spaces with little airflow. It carries THC along with many of the same harmful compounds found in tobacco smoke, including fine particulate matter, tar, carbon monoxide, and cancer-linked chemicals such as benzene. Outdoors or in well-ventilated rooms, exposure drops sharply, and a brief encounter is unlikely to cause lasting harm.
What is in secondhand cannabis smoke?
When cannabis flower burns, it releases a complex mixture that bystanders breathe in along with the user. The composition overlaps heavily with secondhand tobacco smoke, though THC is unique to cannabis.
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- THC and other cannabinoids
- Fine particulate matter (PM2.5) that reaches deep into the lungs
- Tar and carbon monoxide
- Volatile organic compounds and polycyclic aromatic hydrocarbons
- Irritants such as ammonia and hydrogen cyanide
How does secondhand cannabis smoke affect nonsmokers?
Can you get high from secondhand cannabis smoke?
Yes, but usually only mildly and mainly in small, unventilated spaces. A 2016 study in a ventilated room found that nonsmokers exposed to secondhand cannabis smoke reported light subjective effects and had measurable THC in blood, without significant cognitive impairment. Being in a closed car or small room with heavy smoking raises the odds of noticeable effects.
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Does it affect the heart and blood vessels?
Animal research published in the Journal of the American Heart Association found that a single minute of secondhand cannabis smoke impaired endothelial function, the ability of blood vessels to relax, with effects lasting longer than those seen after secondhand tobacco smoke. Short-term exposure can also nudge heart rate and blood pressure upward, which matters most for people with existing heart conditions.
What about the lungs and airways?
Common reactions include coughing, wheezing, sore throat, eye irritation, and headache. For people with asthma, COPD, or allergies, secondhand cannabis smoke can trigger flare-ups, and repeated household exposure is linked to bronchitis-type symptoms in both adults and children.
Who is most at risk from secondhand cannabis smoke?
- Infants and children, whose lungs and brains are still developing
- Pregnant people, because THC and carbon monoxide can affect fetal development
- People with asthma, COPD, or cardiovascular disease
- Anyone with a cannabis sensitivity or a drug test on the horizon
- Pets, especially dogs, which are highly sensitive to THC
Can secondhand smoke make you fail a drug test?
Casual exposure is rarely enough to trigger a positive on a standard urine screen, which typically uses a 50 ng/mL cutoff. Cases of positive results from secondhand exposure do exist, and they usually involve children or adults in extreme, unventilated conditions. If a test is scheduled, avoid enclosed smoking areas rather than relying on secondhand exposure being undetectable.
How can you reduce secondhand cannabis smoke exposure?
- Smoke outdoors, away from doors, windows, and air intakes.
- Never smoke in a moving or parked car with other people inside.
- Choose vaporizers, edibles, or tinctures, which produce far less sidestream smoke.
- Run a HEPA air purifier and open windows when indoor smoking is unavoidable.
- Set clear household rules, especially in homes with children, pregnant people, or pets.
- Keep a short distance and limit time in smoky rooms.
Is secondhand cannabis smoke worse than secondhand tobacco smoke?
Neither is safe, and both deliver fine particles, carbon monoxide, and irritants that harm the lungs and heart. Cannabis smoke can contain more tar per puff than tobacco smoke, while tobacco smoke has a longer, deeper record of causing cancer in bystanders. The practical takeaway is the same: keep combustion smoke away from people who are not using it.
The bottom line
Secondhand cannabis smoke is not harmless. It can produce mild intoxication, irritate the airways and eyes, and temporarily impair blood vessel function, with the biggest risks falling on children, pregnant people, and those with heart or lung disease. Smoking outdoors or switching to smoke-free cannabis products keeps the experience yours.