What Are the Health Impacts of Secondhand Cannabis Smoke?
Secondhand cannabis smoke carries many of the same harmful compounds as tobacco smoke, including fine particulate matter, tar, carbon monoxide, ammonia, and cancer-linked chemicals. Breathing it can irritate the eyes, nose, throat, and lungs, trigger coughing and wheezing, and strain the heart and blood vessels. The CDC confirms that secondhand marijuana smoke also contains THC, the compound that causes a high, so bystanders can absorb an active drug they did not choose to use.
What Is in Secondhand Cannabis Smoke?
Burning cannabis flower releases a complex mix of gases and particles. Many of these overlap with what burning tobacco produces.
exposure to secondhand cannabis smoke
- Fine particulate matter (PM2.5), small enough to reach deep lung tissue and enter the bloodstream
- Tar and polycyclic aromatic hydrocarbons, several of which are known carcinogens
- Carbon monoxide, which reduces oxygen delivery in the body
- THC and other cannabinoids, which nearby people can inhale
- Ammonia, hydrogen cyanide, and other respiratory irritants
Can Secondhand Cannabis Smoke Get You High or Cause a Positive Drug Test?
Yes, in some settings. Studies of nonsmokers in poorly ventilated rooms have found measurable THC in blood and THC metabolites in urine after hours of exposure. Children in a car or small room with a smoker show the highest levels. Effects are usually mild, but a positive drug screen after intense exposure is possible.
Secondhand Cannabis Smoke: Effects on Nonsmokers
How Does Secondhand Cannabis Smoke Affect the Heart and Blood Vessels?
Fine particles from smoke trigger inflammation and can make blood vessels stiffen and function poorly within minutes of exposure. The American Heart Association links short-term particulate exposure to higher risk of heart attack, stroke, and arrhythmia, particularly in people with existing heart disease. Those risks apply to smoke from any plant material, cannabis included.
How Does It Affect the Lungs and Breathing?
Secondhand smoke inflames airways and can cause coughing, wheezing, chest tightness, and shortness of breath. The American Lung Association warns that secondhand smoke of any kind harms lung health and worsens asthma and COPD. People with existing lung conditions react at lower exposure levels.
Who Is Most at Risk?
- Infants and children, whose lungs and brains are still developing
- Pregnant people, because carbon monoxide and THC cross the placenta
- Older adults and anyone with asthma, COPD, or heart disease
- Pets, which inhale concentrated smoke in enclosed homes
Does Ventilation or an Open Window Help?
Partly, but not fully. An open window or a running fan lowers smoke concentration, yet particles linger in the air and settle on surfaces for hours. Smoking outdoors, away from doorways and other people, is the most reliable way to protect bystanders.
Are There Smoke-Free Options for Cannabinoids?
Anyone worried about secondhand exposure can choose products that produce no smoke at all. Lab-tested CBD oils, tinctures, capsules, and topicals deliver cannabinoids without combustion, so no smoke particles enter the air around you. A certificate of analysis from an accredited lab confirms potency and purity before you buy.