Secondhand Marijuana Smoke: Health Consequences and Policy Considerations


Smoke is Smoke

“Breathing any smoke is bad for your health, whether the smoke comes from campfires, tobacco, or marijuana.”

Colorado Department of Health and Environment


What is Secondhand Marijuana Smoke?


Š      Burning the components of plants in the genus Cannabis creates marijuana smoke.


Š      Secondhand marijuana smoke is a complex chemical mixture of smoke emitted from a marijuana cigarette (e.g., joint, spliff), pipe, cigar or cigarillos containing marijuana (e.g., blunts) and smoke that is exhaled.


Š      Marijuana and tobacco smoke are chemically similar and have some of the same cancer-causing and toxic chemicals including: acetaldehyde, ammonia arsenic, benzene, cadmium, chromium, formaldehyde, hydrogen cyanide, isoprene, lead, mercury, nickel, and quinoline.


Š      Marijuana also can be contaminated with mold, insecticides or other chemicals that may be released in secondhand smoke.



What are the Health Risks?


            According to the Colorado Department of Health and Environment, “Secondhand smoke from marijuana has many of the same chemicals as smoke from tobacco, including those linked to lung cancer. While more studies are needed, secondhand smoke from marijuana may increase the risk of lung cancer.  Also, secondhand smoke from marijuana can cause lung irritation and asthma attacks, and makes respiratory infections more likely.  If you have children or non-users in your family or home, it is important to practice safer smoking behaviors, like not smoking indoors or in your car.”


            Since marijuana is illegal by federal law there have been a limited number of studies examining health risks associated with marijuana use in the United States.   Health risks may also be difficult to determine as marijuana is often used by tobacco users and/or in combination with tobacco. Some examples of concurrent use are:


Š      Mixing marijuana and tobacco in marijuana papers and in some electronic smoking devices

Š      Rolling blunts (marijuana wrapped inside tobacco leaf, cigar, or cigarillo)

Š      Blunt chasing (smoking a tobacco cigarette after smoking marijuana)


            Recent studies indicate that exposure to secondhand marijuana smoke may present a public health hazard.


Š      A 2007 Canadian government–affiliated study found a number of toxic and cancer-causing chemicals in secondhand marijuana smoke including three-times the amount of ammonia in secondhand marijuana smoke than in tobacco smoke  as well as other chemicals such as mercury, cadmium, nickel, lead, chromium, hydrogen cyanide, benzene, isoprene, toluene, and others.


Š      Marijuana smoke was added to the list of chemicals known to cause cancer and reproductive toxicity under the Safe Drinking Water and Toxic Enforcement Act (Proposition 65) in California in 2009 by the California Environmental Protection Agency.   In its report on marijuana the agency identified at least 33 individual constituents present in both marijuana smoke and tobacco smoke that are Proposition 65 carcinogens.


Š      A 2014 study of rats conducted by researchers at the University of California at San Francisco found substantial impairment of blood-vessel function from 30 minutes of exposure to secondhand marijuana smoke at levels comparable to those found in restaurants that allow cigarette smoking.  The researchers found that rats exposed to secondhand marijuana smoke experienced a greater than 50 percent reduction in flow-mediated dilation, similar to the reduction in artery function seen in both rats and humans exposed to tobacco smoke in previous studies.  The researchers stated in a press release that because of their similar chemical composition, “secondhand marijuana smoke and secondhand tobacco smoke are likely to have similar harmful effects on public health, including atherosclerosis (partially blocked arteries), heart attack, and stroke.”


Š      One in six infants and toddlers admitted to a Colorado hospital with coughing, wheezing, and other symptoms of bronchiolitis tested positive for marijuana exposure. The study, "Marijuana Exposure in Children Hospitalized for Bronchiolitis," recruited parents of previously healthy children between one month of age and two years old who were admitted to Children's Hospital Colorado (CHC) between January 2013 and April 2014 with bronchiolitis, an inflammation of the smallest air passages in the lung.


Š      Do electronic smoking devices (ESDs) with marijuana emit hazardous chemicals?  ESDs require certain chemicals for their operation and are known “to emit ultrafine particles and low levels of toxins that are known to cause cancer.”   A 2015 study found that “ESD aerosol particles are smaller than 1000 nanometers, which is a similar size to tobacco smoke and diesel engine smoke, and bystanders can be exposed to this aerosol. The exact size distribution depends on the chemical composition of the electronic cigarette liquid, the e-cigarette device operation, and user vaping preferences.”


Why Should Marijuana Smoking be Limited in any Public Place or Workplaces?


Š      Everyone should have the right to breathe smoke-free air.  Smoke-free policies are designed to protect the public and all workers from the exposure to the hazardous chemicals found in secondhand tobacco smoke. The same should be true for secondhand marijuana smoke.


Š      For consistency and enforcement, smoke-free policies in public places and workplaces should apply to tobacco and marijuana whether vaped or smoked.   Allowing marijuana smoking in places where smoking is now prohibited could undermine Colorado laws that protect the public from exposure to secondhand tobacco smoke and pave the way for the return of tobacco smoking in restaurants, bars, or other work places or public places. It may violate the section of Amendment 64 that says that nothing in the law shall “permit consumption that is conducted openly and publicly or in a manner that endangers others.”  Secondhand marijuana smoke or emissions from electronic smoking devices may endanger the health of others.


Š      Ventilation will not solve the problem. The American Society for Heating, Refrigeration, and Air Conditioning Engineering (ASHRAE), the organization that develops engineering standards for building ventilation systems, now bases its ventilation standards for acceptable indoor air quality on an environment that is completely free from secondhand tobacco smoke, secondhand marijuana smoke, and emissions from electronic smoking devices.


Š      Smoke-free policies provide incentives to quit smoking, and help renormalize smoking behavior, and are particularly effective among youth and young adults who are vulnerable to visual cues and social norms of smoking. It is likely that for marijuana smoke-free policies will have a similar effect.


In the interest of public health, the exposure to emissions from marijuana smoking or vaping should be prohibited wherever tobacco smoking is prohibited.


The Group to Alleviate Smoking Pollution‘s Position on Marijuana Smoking


            The mission of the Group to Alleviate Smoking Pollution (GASP of Colorado) is to eliminate secondhand-smoke exposure at work, in public places, and in multiunit housing through education and policy change.  GASP takes no position on whether marijuana should be legal.  Like tobacco, GASP has no objection to people using marijuana as long as it is done in places where it will not harm others.  Nobody should have to breathe secondhand marijuana smoke against their will at work, in public, or where they live.


            While the scientific research on the effects of secondhand marijuana smoke is not as extensive as the research about secondhand tobacco smoke, recent studies indicate that secondhand marijuana smoke contains some of the same harmful chemicals as tobacco smoke and may impair blood vessel function.  Therefore, people should avoid exposure to secondhand marijuana smoke and it should not be allowed in public places, workplaces, and multiunit residential buildings.


            The Group to Alleviate Smoking Pollution (GASP of Colorado) is a 501-C-3 statewide nonprofit organization working to eliminate secondhand smoke from the air we breathe at work, in public places, and in multiunit housing.  Visit for more information.


Visit for more information about secondhand marijuana smoke.


May be reprinted or copied with appropriate attribution to the

Group to Alleviate Smoking Pollution (GASP of Colorado) © May 2017




Health and Safety Code section 25249.8(b) and Title 27, Cal Code of Regs., section 25302 et seq. Accessed online at:


Xiaoyin Wang, Ronak Derakhshandeh, Shilpa Narayan, Emmy Luu, Stephenie Le, Olivia M Danforth, Hilda J Rodriguez, Richard E Sievers, Suzaynn F Schick, Stanton A Glantz, and Matthew L Springer. Brief Exposure to Marijuana Secondhand Smoke Impairs Vascular Endothelial Function. Circulation. 2014;130:A19538.


David Moir, William S. Rickert, Genevieve Levasseur, Yolande Larose, Rebecca Maertens, Paul White, and Suzanne Desjardins. A Comparison of Mainstream and Sidestream Marijuana and Tobacco Cigarette Smoke Produced Under Two Machine Smoking Conditions. Chem. Res. Toxicol, Published on Web 12/07/2007


Thornburg, J.; Malloy, Q.; Cho, S.; Studabaker, W.; Lee, Y.O., "Exhaled electronic cigarette emissions: what's your secondhand exposure?," RTI Press Research Brief: 1-4, March 2015.


ASHRAE 2015 Ventilation for Acceptable Indoor Air Quality Library/docLib/StdsAddenda/62_1_2013_2015Supplement_20150203.pdf


Marijuana Exposure in Children Hospitalized for Bronchiolitis


Fact sheet about electronic smoking devices