Does Smoking Marijuana Cause Lung Cancer?

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The link between smoking tobacco and lung cancer is undeniable, but does smoking marijuana cause lung cancer, too? The short answer—maybe. Let's take a look at the long answer and the effects that smoking marijuana can have on the lungs.

effects of marijuana on the lungs
Illustration by Brianna Gilmartin, Verywell

Studies Looking at Marijuana and Lung Cancer

In 2006, many of us in medicine were shocked when a review of research to date did not show an increase in lung cancer related to marijuana use. There was even a suggestion that marijuana had a protective effect against lung cancer. More recent studies, in contrast, do appear to link smoking marijuana with lung cancer, although the results are mixed, and much uncertainty remains.

One study demonstrated a doubling in lung cancer for male marijuana smokers who also used tobacco (i.e., for men who smoked the same amount, the risk of lung cancer was twice as high for men who also used marijuana). Another study found that long-term use of marijuana increased the risk of lung cancer in young adults (in this study defined as age 55 and under), with the risk increasing in proportion to the amount of marijuana smoked.

A large international study conducted in 2015, in contrast, found little association between habitual and long-term use of cannabis and lung cancer. In this review, some association was found between cannabis use and lung adenocarcinoma but no association 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 concerns include the fact that many of the studies to date have been small studies, those that have been done have often included small numbers of heavy marijuana smokers, marijuana use, in general, is self-reported, and 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 reach 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. There have also been reports of an increase in respiratory symptoms such as wheezing, shortness of breath, and persistent coughing in people who smoke pot. That said, regular smoking of marijuana does not seem to cause any significant changes in lung function, nor does it appear to increase the risk of COPD, and COPD is an independent risk factor for lung cancer.

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

The Controversy About Marijuana and Cancer Risk

Since marijuana is still illegal in the U.S. under federal law, it is hard to do the controlled studies 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.

The bottom line on marijuana use and risk of cancer? Though marijuana most likely pales in cancer risk when compared to cigarette smoking, it's best to practice caution. There are reasons in addition to lung cancer risk (and the fact that it is illegal in many states) to avoid marijuana.

Marijuana likely increases the risk of testicular cancer, prostate cancer, cervical cancer, a type of brain tumor, and the risk of leukemia in the offspring of women who use weed during pregnancy.

The Flip Side: Marijuana in Cancer Patients

When we talk about marijuana and cancer, there are generally two different discussions. When talking about the cause of cancer, results are still mixed with some studies suggesting that marijuana smoking increases the risk of cancer and others saying that marijuana may instead protect against cancer.

What we do know, is that 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, and sleep disturbances. And since 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 percent of people with cancer, the use of cannabinoids by cancer patients deserves much further study.

As far as treatment, 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. Hopefully, with legalization across the United States increasing, this answer will become clearer in the future. 

Secondhand Marijuana Smoke

A final concern about marijuana is the possible effects of marijuana on nearby nonusers. The effects of secondhand marijuana smoke on health and drug testing are being studied. 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.

A Word From Verywell

As far as cancer risk, many oncologists are rethinking the previous shoot-from-the-hip reactions that marijuana is bad. From what we have learned about cigarette smoking and lung cancer it was feared that cannabis smoking would cause similar problems, but this hasn't been demonstrated at this time.

In contrast, the possible benefit of cannabis to people living with cancer and complications of cancer deserves further attention. At this time we have little to assist people who are developing or have developed cancer cachexia. Through its effect on appetite, cannabis might be a relatively easy option for addressing the poor appetite so common among cancer patients.

Of greatest interest perhaps at the present time is the reduction in the need for opioid pain medications in people with cancer who have used cannabis. Given the epidemic of opioid overdoses superimposed on pain medications many people with cancer were reluctant to use in the first place is concerning. It was thought that the majority of people in the end stages of cancer were grossly undertreated for pain even before national attention was directed at the opioid crisis. 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.

13 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."