Does Smoking Marijuana Cause Lung Cancer?

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Smoking marijuana and the link to lung cancer isn't supported by the same body of research that makes clear the link between lung cancer and cigarette smoking. That said, studies continue to reveal new findings about the risks associated with smoking marijuana.

Some marijuana users report respiratory symptoms like shortness of breath and wheezing due to marijuana use, and there are studies to suggest marijuana smoke causes lung damage. What's less clear are the long-term effects of marijuana use.

This article presents some of the research on smoking marijuana and lung cancer, as well as some findings on how cannabis may help as a treatment for people living with cancer.

effects of marijuana on the lungs

Verywell / Brianna Gilmartin

Studies on Marijuana and Lung Cancer

A definitive link between marijuana and lung cancer has proven elusive. Early research studies found a higher risk of lung cancer in male marijuana smokers who also used tobacco, as well as an increased risk with long-term use leading to lung cancer in young adults. On the other hand, some evidence pointed to marijuana use having a protective effect.

In 2015, a large international study found little association between habitual and long-term use of cannabis and lung cancer. Some association was found between cannabis use and lung adenocarcinoma. None was found between cannabis use and squamous cell carcinoma of the lungs.

A 2018 study published in the Journal of Thoracic Oncology summarized some of the difficulties both in knowing whether marijuana use is associated with lung cancer, and how well marijuana may work to control symptoms in people living with cancer. Some of these factors are:

  • The small size of the studies
  • The self-reported nature of marijuana use
  • The low numbers of heavy marijuana users included in studies
  • The combination of tobacco smoking along with marijuana use

The size and quality of studies on marijuana smoking and lung cancer make it difficult to arrive at firm conclusions.

Effects of Marijuana on the Lungs

Researchers have found that regular use of marijuana causes injury to the airways that can be seen visibly as well as under the microscope. People report increased respiratory symptoms such as:

  • Wheezing
  • Shortness of breath
  • Persistent cough

Yet marijuana use does not seem to cause any significant changes in lung function. It also doesn't appear to increase the risk of COPD, which is an independent risk factor for lung cancer.

Marijuana Use and Lung Transplants

A 2017 study looking at the effect of cannabis smoking on the quality of lungs to be used for transplant. It found that a history of cannabis did not have any effect on transplant outcomes, and that including former cannabis smokers could potentially improve the donor pool. Smoking marijuana does not appear to cause significant changes in lung function.

Marijuana and Cancer Risk Controversy

Since marijuana is still illegal in the U.S. under federal law, it is hard to do the controlled studies on smoking marijuana that have been done with tobacco. Because of this, it helps to look at what we do know about marijuana that suggest it could increase lung cancer risk:

  • Many of the carcinogens and co-carcinogens present in tobacco smoke are also present in smoke from marijuana.
  • Marijuana smoking does cause inflammation and cell damage, and it has been associated with pre-cancerous changes in lung tissue.
  • Marijuana has been shown to cause immune system dysfunction, which could theoretically predispose individuals to cancer.

Marijuana use most likely pales in comparison to cigarette smoking when it comes to cancer risk but it's best to practice caution. There are reasons beyond lung cancer risk to avoid marijuana, which remains illegal in many states.

Marijuana and Pregnancy

Studies suggest that marijuana use during pregnancy may lead to fetal harm, including congenital defects, developmental (learning) disabilities, and miscarriage. The effects may increase when marijuana is smoked, adding toxins that also are harmful.

Marijuana in Cancer Patients

The link between marijuana use and cancer also can mean marijuana as a treatment option rather than cause of lung cancer. Smoking marijuana may help some people cope with cancer.

According to the National Cancer Institute, "cannabinoids may have benefits in treating cancer-related side effects."Some of the side effects that may improve with the use of weed include:

  • Nausea
  • Loss of appetite
  • Pain
  • Sleep disturbances

Cancer cachexia—a combination of symptoms including loss of appetite, unintentional weight loss, and muscle wasting—is considered the direct cause of death in 20% of people diagnosed with cancer. So the potential of cannabinoids in cancer treatment deserves much further study.

The difficulty in studying an illegal substance has limited research. Some studies found that marijuana may have had a benefit in patients with a type of recurrent brain tumor.With trends toward legalization across the United States, this answer will become clearer in the future. 

Secondhand Marijuana Smoke

Marijuana use also may have secondhand smoke effects. Some studies have found marijuana smoke to be as much of a concern as tobacco smoke, so caution may be warranted.

Until large studies can be performed, you can't be assured that smoking marijuana or being exposed to secondhand weed smoke has no health concerns.

You have a variety of choices other than smoking for ways to use medical cannabis and recreational cannabis in states where it is legal. If you worry about your lung health and exposing nonsmokers, it may be best consider a different mode of delivery than smoking, such as edibles.


Marijuana use may increase your risk of lung cancer, but more research is needed to determine a clear link. Studies to date have delivered mixed results on whether and how marijuana smoke adds to the risk or, with some results, appears to have a protective effect against lung cancer.

People report wheezing, coughing, and other respiratory symptoms with marijuana use. Some evidence shows that it can lead to precancerous changes in the lungs. However, questions remain about long-term damage. If using marijuana, you may wish to consider edibles and other alternatives.

Cannabis remains an option for pain management in people living with cancer, as well as its use to improve appetite in the face of cancer cachexia complications.

A Word From Verywell

For people living with cancer, cannabis use may offer an alternative to opioid pain medications in some cases. The opioid crisis has added to concerns that people facing cancer-related pain are undertreated. It may be that the legalization of marijuana in many states, whether for recreational or medical use, has arrived at the right time to address this problem.

10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Lynne Eldridge, MD
 Lynne Eldrige, MD, is a lung cancer physician, patient advocate, and award-winning author of "Avoiding Cancer One Day at a Time."