What are the Effects of Secondhand Cannabis Smoke?
The effects of secondhand cannabis smoke are similar to those of secondhand cigarette smoke. Secondhand cannabis smoke can contain many of the same toxins and carcinogens as cigarette smoke, leading to an increased risk of lung cancer and other respiratory problems. Secondhand cannabis smoke can cause symptoms such as dizziness, headache, nausea, and eye and throat irritation.
This article was originally published on January 25, 2023 and last updated on December 30, 2025.
Exposure to cannabis smoke
Secondhand cannabis smoke contains tetrahydrocannabinol (THC), the compound responsible for cannabis’s psychoactive effects. According to the CDC, secondhand exposure to THC can affect children and adolescents, potentially causing adverse health effects and impacting brain development. However, more research is needed to understand the full extent of these effects.
What is secondhand marijuana smoke?
Marijuana smoke is created by burning components of plants in the genus Cannabis.
- The terms marijuana and cannabis are often used interchangeably when discussing the smoking and vaping of the cannabis plant and its components, and the secondhand smoke created by combusting the product.
- Secondhand marijuana smoke is a complex chemical mixture of smoke emitted from combusted marijuana and the smoke that is exhaled by the user.
- Secondhand marijuana smoke contains fine particulate matter that can be breathed deeply into the lungs.
- Secondhand marijuana smoke contains many of the same cancer-causing substances and toxic chemicals as secondhand tobacco smoke. Some of the known carcinogens or toxins present in marijuana smoke include: acetaldehyde, ammonia arsenic, benzene, cadmium, chromium, formaldehyde, hydrogen cyanide, isoprene, lead, mercury, nickel, and quinoline.i
- Marijuana smoke contains tetrahydrocannabinol (THC), the active chemical in cannabis.
What are the health risks of exposure to secondhand marijuana smoke?
Short-term effects include coughing, headaches, eye and nasal irritation, and sore throat. Long-term effects may lead to increased risk of coronary heart disease, lung cancer, stroke, and chronic obstructive pulmonary disease (COPD).
Children may experience sudden infant death syndrome (SIDS), respiratory and ear infections, asthma attacks, and slowed lung growth. Pregnant women may be at risk for premature birth and low birth weight. Additionally, for lung cancer patients, exposure may lead to reduced overall survival and progression-free survival.
The 2024 U.S. Surgeon General’s Report found that “secondhand cannabis smoke contains many of the same toxic and cancer-causing chemicals found in tobacco smoke, and some of those chemicals are found in higher amounts in secondhand cannabis smoke than in secondhand tobacco smoke.”
Peer-reviewed and published studies indicate that exposure to secondhand marijuana smoke may have health and safety risks for the public, mainly due to its similar composition to secondhand tobacco smoke.
Secondhand smoke from combusted marijuana contains delicate particulate matter that can be breathed deeply into the lungs, which can cause lung irritation, asthma attacks, and make respiratory infections more likely. Exposure to fine particulate matter can exacerbate health problems, particularly for individuals with respiratory conditions such as asthma, bronchitis, or COPD.
Particulate levels from secondhand marijuana smoke are even higher than particulate levels from secondhand tobacco smoke. A study comparing indoor particulate matter 2.5 (PM2.5) levels from secondhand marijuana smoke and secondhand tobacco smoke concluded that “the average PM2.5 emission rate of the pre-rolled marijuana joints was found to be 3.5 times the average emission rate of Marlboro tobacco cigarettes, the most popular US cigarette brand.” Smoking a marijuana joint indoors can produce extremely high indoor PM2.5 concentrations, thereby exposing the public and workers to dangerous secondhand marijuana smoke emissions.
Being near people who are using inhaled cannabis is hazardous to human health. In a dispensary that allowed marijuana/cannabis smoking, research scientists discovered that the average PM2.5 emissions were 840 μg/m3 over nine visits, which exposed patrons and workers to air pollutant concentrations that are beyond hazardous levels.
The levels of PM2.5, a delicate particulate matter, inside a Los Angeles cannabis consumption lounge were 10 times higher during the lounge’s busiest hours than the particulate levels inside the lounge when the business was closed. They were 3 times higher than the levels during slower times of day.
Ultrafine particles go deep into the lungs and can cause asthma, upper respiratory disease, and more. Researchers studied the smoke from cannabis cigarettes and discovered that smoking cannabis in ozone-rich environments, both indoors and outdoors, will likely lead to ultrafine particle (UFP) formation.
On-site consumption of cannabis using electric vaporizers, vape pens, and dab rigs produces a chemical aerosol that pollutes indoor air to unhealthy levels. This diminished air quality was observed when marijuana was not being combusted on-site. Researchers measured high levels of PM2.5 inside a marijuana retailer that allowed vaporizing, dabbing, and vaping marijuana, but did not allow smoking of marijuana or tobacco.
Researchers at the University of California at Berkeley studying fine particulate matter exposure found that cannabis bong smoking in the home generated 4 times greater PM2.5 concentrations than cigarette or tobacco hookah (waterpipe) smoking.
Among adults living in a state with legalized medical cannabis and limited smoke-free protections, researchers found that secondhand cannabis smoke exposure is common and associated with more frequent respiratory symptoms, particularly among cannabis users. Those exposed were more socially and economically vulnerable.
In the first “whole-house” study of its kind, researchers measured both tobacco and marijuana secondhand smoke. They found that PM2.5 concentrations from marijuana secondhand smoke were 4.4 times higher than emissions from secondhand tobacco smoke. Secondhand marijuana levels were higher than tobacco levels in every room of the house.
Children who live in households where cannabis is smoked indoors have biomarkers of cannabis secondhand smoke exposure that were 5 times higher than those of children who are not exposed to cannabis secondhand smoke in the home.
Significant amounts of mercury, cadmium, nickel, lead, hydrogen cyanide, and chromium, as well as 3 times the amount of ammonia, are found in mainstream marijuana smoke than in tobacco smoke.
What does exposure to secondhand marijuana smoke do?
In 2009, the California Office of Environmental Health Hazard Assessment added marijuana smoke to its Proposition 65 list of carcinogens and reproductive toxins, also known as the Safe Drinking Water and Toxic Enforcement Act of 1986. It reported that at least 33 individual constituents present in both marijuana smoke and tobacco smoke are Proposition 65 carcinogens.
Secondhand smoke from marijuana has many of the same chemicals as smoke from tobacco, including those linked to lung cancer.
Exposure to secondhand marijuana smoke impairs blood vessel function. Published studies on rats show that thirty minutes of exposure to secondhand marijuana smoke at levels comparable to those found in restaurants that allow cigarette smoking led to substantial impairment of blood vessel function. Marijuana smoke exposure had a greater and longer-lasting effect on blood vessel function than exposure to secondhand tobacco smoke.
One minute of exposure to marijuana SHS substantially impairs endothelial function in rats for at least 90 minutes, considerably longer than comparable impairment by tobacco SHS. The findings in rats suggest that SHS can exert similar adverse cardiovascular effects regardless of whether it is from tobacco or marijuana.
How are secondhand marijuana smoke and secondhand tobacco smoke similar?
Secondhand marijuana smoke and secondhand tobacco smoke are similar in many ways. More research is needed, but the current body of science shows that both tobacco and marijuana smoke have identical chemical composition and suggests that they may have harmful cardiovascular health effects, such as atherosclerosis (partially blocked arteries), heart attack, and stroke.
Particle concentrations from dabbing and vaporizing cannabis can create levels of indoor air pollution similar to those seen in extreme air pollution events like wildfires and severe industrial pollution. Exposure at these concentrations can cause cardiovascular and respiratory disease.
Vaporized CBD produces significantly higher concentrations of formaldehyde, acetaldehyde, acrolein, diacetyl, and methylglyoxal compared with the other cannabinoid samples. Compared with different modalities of use for CBD and other cannabinoids, vaping has the potential to adversely impact human health by producing harmful products during the heated aerosolization process.
People who are exposed to secondhand marijuana smoke can have detectable levels of THC (tetrahydrocannabinol) in their blood and urine.
Marijuana also can be contaminated with mold, insecticides, or other chemicals that may be released in secondhand smoke.
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