Is Marijuana a Risk Factor or a Treatment Option for Lung Cancer?

We've known for a long time that smoking tobacco cigarettes is the No. 1 risk factor for developing lung cancer. The Centers for Disease Control and Prevention reports that "in the United States, cigarette smoking is linked to about 80 percent to 90 percent of lung cancers. Using other tobacco products such as cigars or pipes also increases the risk for lung cancer." But what about that other smoke-able substance, marijuana? Can smoking cannabis -- another term for the weed that's garnered a lot of attention in recent years as a potential medicine -- put you at higher risk of developing lung cancer down the road?

It seems the answer is currently "no," but one of the challenges in determining whether smoking marijuana is a risk factor for lung cancer is because it often occurs in addition to or alongside tobacco cigarette smoking. "There has been quite a bit of literature published on the effects of marijuana smoking on lung health," says Dr. Russell Bowler, professor of medicine and director of the COPD clinic at National Jewish Health in Denver, but these studies are "always complicated by the fact that many marijuana smokers also smoke tobacco cigarettes, so the trick is to distinguish the effects of tobacco from the effects of marijuana smoking."

[See: 7 Things You Didn't Know About Lung Cancer.]

Because marijuana smoke contains many of the same toxins that tobacco smoke contains, "it's reasonable to be concerned that marijuana smoke might be toxic to the lungs," Bowler says. But conclusive evidence of a causal link hasn't yet been proven. "I think the data are mixed on lung cancer. There has not been really conclusive evidence that marijuana smoking is related to lung cancer."

Dr. William Checkley, a pulmonary critical care physician and associate professor of medicine, international health and biostatics at Johns Hopkins University in Baltimore, also says a causal link has not been established between marijuana smoking and lung cancer. Checkley was part of the multi-disciplinary team of doctors and researchers who produced a 2017 report from the National Academies of Sciences, Engineering and Medicine titled " The Health Effects of Cannabis and Cannabinoids" that looked at our current understanding of marijuana's risks and uses.

"We had an opportunity to evaluate systematic reviews or reviews that pulled information from multiple studies, and within that particular systematic review that looked at information from a large number of individuals -- it was close to 5,000 individuals -- there was no link between people who used cannabis habitually [getting lung cancer] versus those who were non-habitual or never users," Checkley says.

The committee also looked at whether dosage played a role in a person's risk for developing lung cancer from using marijuana, and found "there was not a very clear signal." But Checkley cautions that there are some fundamental issues with how the data is collected -- through self-reporting by users -- and there are many variables that can't always be controlled for in observational studies, such as which smoking technique a user favors, the strain of marijuana being used and the use of tobacco cigarettes, too.

Determining whether there's a dose-response aspect to lung cancer risk from cannabis smoking is also challenging, "because there were fewer people who were heavy and chronic cannabis users," Checkley says. The group of habitual or chronic users was small, so statistically speaking, any causal effect becomes harder to prove.

Checkley says the committee did find a "slightly higher chance of having adenocarcinoma if you were a habitual [marijuana] smoker than if you were not or a never-user." Adenocarcinoma is type of cancer that forms in mucus-secreting glands, such as the lungs, prostate, pancreas, esophagus and colon. "Nevertheless, I think that evidence was still weak, and the association was still not statistically significant, despite the fact that it showed there was some suggestion of increased risk," he says.

This means that while it's reasonable to think there could be a connection between inhaling a substance like marijuana into the lungs and the subsequent development of lung disease, a direct line between smoking pot and getting lung cancer hasn't been established.

[See: What Not to Say to Someone With Lung Cancer.]

But what about using cannabis as a treatment option for lung cancer patients? As marijuana has become more widely available in the 29 states (and District of Columbia) that have legalized it for medical and/or recreational use, some people are wondering whether it might have applications in the treatment of cancer or the side effects of more conventional forms of cancer treatment. (It should be noted here that marijuana is still illegal at the federal level and in January 2018, the Trump administration vowed to prosecute violators regardless of whether they're using medical marijuana in a state that has legalized it, potentially putting a major damper on the burgeoning cannabis industry in states that had previously legalized it.)

The American Cancer Society reports that, "relying on marijuana alone as treatment while avoiding or delaying conventional medical care for cancer may have serious health consequences." But there is data supporting the use of cannabis as an alternative or complementary therapy alongside conventional treatment. Several studies have shown cannabis may be very good at helping patients alleviate the pain, nausea, vomiting and sleeplessness that often accompany treatment for cancer. "In our report, we found that there was conclusive evidence that medicines derived from cannabis, such as oral cannabinoids, were effective antiemetics, so they helped to treat the nausea and vomiting that is linked to side effects of chemotherapy," Checkley says, adding "I think there's substantial evidence that cannabis is a substantial therapy for pain."

Sid Taubenfeld, CEO of TO Pharma, a New York--based biopharmaceutical company affiliated with Tikun Olam, an Israeli company that produces medical cannabis and is studying its applications to treat various conditions, says that recent results of a study conducted by Tikun Olam and published in the European Journal of Internal Medicine found cannabis had a remarkable effect on the pain, nausea, sleep problems and decreased appetite many cancer patients experience. The study followed 2,970 cancer patients treated with Tikun Olam--developed strains of cannabis between 2015 and 2017. According to the study, 95.9 percent of participants reported an improvement in their condition with the use of cannabis. "We've really shown that in terms of the total population, 95.9 percent had improvement in quality of life, which is pretty amazing," Taubenfeld says.

Particularly for patients who had severe pain (reporting an 8 out of 10 or higher on the standard 1 to 10 pain scale most doctors use), Taubenfeld says the results were encouraging. Many of these patients rely on opioids to deal with the pain that's often associated with late-stage cancer, but the study "showed we could reduce the use of opioids. Thirty-six percent of our patients stopped [taking] opioids altogether, and 10 percent reduced their dose. I'm sure you're aware of the opioid epidemic and what's going on now. The data is out there that cannabis could clearly be a substitute for opioids," he says.

Taubenfeld says the company is looking at other applications of cannabis -- including treatment of agitation in Alzheimer's disease, Crohn's and colitis and epilepsy. However, one of the challenges with studying the effects of medical marijuana is that because it's still illegal at the federal level and classified by the Drug Enforcement Administration as a Schedule 1 drug, (meaning "drugs with no currently accepted medical use and a high potential for abuse" -- alongside heroin, LSD and ecstasy) it's difficult to run a study without running afoul of the law.

[See: 7 Innovations in Cancer Therapy.]

"It's hard for us to do studies against OxyContin," a widely used and abused opioid, "which is Schedule 2. I think the government has to get a little more science-oriented and a little less political," Taubenfeld says. Therefore, the company conducts its studies in Israel in an effort to develop the scientific literature required for marijuana to gain wider acceptance as a treatment option. "Only through clinical trials will mainstream doctors get on board," he says.

In the meantime, if you're struggling with pain, nausea, vomiting or other side effects of treatment for lung cancer, talk to your doctor. Although marijuana or its components may not be an option for you, your doctor may be able to prescribe other medications or make adjustments to your treatment schedule that will provide some relief.

Elaine K. Howley is a freelance Health reporter at U.S. News. An award-winning writer specializing in health, fitness, sports and history, her work has appeared in numerous print and online publications, including AARP.org, espnW, SWIMMER magazine and Atlas Obscura. She's also a world-record holding marathon swimmer with a passion for animals and beer. Contact her via her website: elainekhowley.com.