The health risks and benefits of marijuana are hotly debated, and one particular risk—lung cancer—isn't as well-studied as it is for say, cigarettes. Here's what you should know about pot and your respiratory health.

August 07, 2017

You’ve heard about the potential health benefits of marijuana: Studies suggest pot may help people with depression, opioid addiction,  nausea, chronic pain, the eye disease glaucoma, and more. At the same time, it’s classified as a schedule 1 drug (with the likes of heroin and Ecstasy) at the federal level, a variety of types and strains make quality control difficult, and some states have reported marijuana-related motor vehicle accidents have increased since legalization.

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In addition, the health risks of marijuana aren't clear—especially when it comes to lung cancer. “There hasn’t been nearly as much research on marijuana as on tobacco as a cause of cancer because of it being largely illegal,” says Otis W. Brawley, MD, the chief medical officer of the American Cancer Society in Atlanta.

Outside of issues with legality, studies have trouble controlling for marijuana use alone. Since many people who smoke pot also smoke tobacco, says Dr. Brawley, determining direct causation between pot and lung cancer is difficult.

Here are three things to consider when it comes to marijuana use and lung cancer.

Any kind of smoke can damage your lungs

Whether it’s tobacco smoke or marijuana smoke, your lungs still suffer, says Robert Schwartz, PhD, senior scientist at the Centre for Addiction and Mental Health in Toronto. “If you're inhaling smoke, it doesn't matter the kind, you're creating damage,” he says. “My motto is you need to take the smoke out of dope.”

According to the American Cancer Society, tobacco contains at least 70 cancer-causing chemicals. About 30 of those 70 chemicals are also present in marijuana, says Dr. Brawley. Studies have found both positive and negative correlations between smoking pot and increased lung cancer risk, but inhaling smoke of any kind harms the lungs.

What about other forms of marijuana consumption, like edibles and vaping? Thorough research has yet to be done on these methods, says Schwarz. Since consuming weed in vapor form still releases particles into the lungs, this method could be a plausible lung-cancer contributor.

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The Canadian Institutes of Health Research (CIHR) funded a recent study to help develop guidelines for marijuana use in Canada, where they are moving towards legalization. “Smoking is the most hazardous method of cannabis use, and we know that smoking causes cancer,” says Steven Hoffman, PhD, a scientific director for CIHR, Ottawa, Ontario. “Health risks are exacerbated by practices such as deep inhalation of smoke. What we don’t know is whether or not cannabis itself causes or possibly even prevents cancer from developing.” The CIHR-funded guidelines include avoiding deep inhalation of cannabis smoke and any synthetic versions of the drug. “To avoid all risks, do not use cannabis,” the guidelines recommend.

There’s a lack of quality control

When marijuana users light up, there’s a chance they’re not only smoking pot, says Schwartz. “In Canada, 30% of people who smoke marijuana mix tobacco in it,” he says. Mixing drugs not only increases carcinogens, but also makes smoking in moderation difficult due to the addictive nature of tobacco.

The CIHR is still determining if people are substituting their cigarette habits for pot, which would be a positive effect of the drug, but Schwarz says it’s unlikely in older populations. “I would find it unlikely that we're going to get huge transfers of cigarette smokers to marijuana, but for young people, they might pick marijuana over cigarettes.”

Strains of marijuana can vary widely too, so the effects of one batch may be different than another. “There might be a chemical that is high in concentration in one stash and that could be great for pain and nausea in cancer patients, but then the next stash that someone buys, that chemical could be low,” explains Dr. Brawley.

What's more, synthetic marijuana—referred to by a number of names including Spice, K-2, Moon Rocks, and more—relies on a mixture of manmade chemicals sprayed onto miscellaneous dried plants and herbs and often incites erratic behavior in users. Synthetic cannabinoids are unregulated and using them can be life-threatening in some cases, warns the National Institute on Drug Abuse.

Big questions are still unanswered

Due to issues with legality, well-controlled and comprehensive studies on marijuana’s effects on the lungs have yet to be conducted. Certain chemicals in marijuana could be helpful for cancer or chronic pain patients and research on these desperately need to be done, says Dr. Brawley. In fact, oncologists can already write prescriptions for pills containing THC, like Marinol, to help with chemotherapy-induced nausea. "This is the part of the story that rarely gets told,” says Dr. Brawley. “We should be more open-minded that there are some medicinal properties in marijuana that may be beneficial when isolated.”

As for studies suggesting marijuana is or is not a detriment to the lungs, take their findings with a grain of salt. “The need for larger sample sizes and long-term studies means there is no definitive answer,” Dr. Brawley says. Just because a study doesn't find a link between marijuana and lung cancer doesn't mean it’s safe, while studies that do find a link may be unreliable too, due to extenuating factors. As long as marijuana is illegal throughout most of the U.S., it will be hard to design a study to get a definitive answer to the question, experts say.