A new study reveals that many people with cancer use marijuana, and rates of use in the U.S. have increased over time. Published early online in CANCER, a peer-reviewed journal of the American Cancer Society, the study also found that patients with cancer are more likely to use prescription opioids than adults without cancer.

Pain is a common symptom of cancer, and many affected patients do not receive adequate pain relief. In light of rapidly evolving marijuana legislation and a growing opioid epidemic, a team led by Jona Hattangadi-Gluth, MD, and Kathryn Ries Tringale, MD, MAS, of the University of California, San Diego, examined trends in the self-disclosed use of marijuana and opioids among patients with cancer.

After analyzing data from the U.S. National Health and Nutrition Examination Survey between 2005 and 2014, the investigators matched 826 people with cancer to 1,652 controls without cancer. Among survey respondents who had cancer, 40.3 percent used marijuana within the past year, compared with 38.0 percent of respondents without cancer. Also, people with cancer were more likely to use prescription opioids than their demographically equivalent counterparts without cancer (13.9 percent versus 6.4 percent).

"Prospective clinical trials are needed to quantify the efficacy of marijuana in cancer-specific pain as well as the risk of opioid misuse in this patient population," said Dr. Tringale.

When looking at rates of marijuana and opioid use in more than 19,000 survey respondents with and without cancer over 10 years, the researchers found significantly increased use of marijuana over time -- likely reflecting increased availability due to legislative changes -- but they found stable rates of opioid use. A diagnosis of cancer did not significantly affect the odds of substance use over time from 2005 to 2014.

"Medical marijuana legalization has previously been associated with a reduction in hospitalizations related to opioid dependence or abuse, suggesting that if patients are in fact substituting marijuana for opioids, this may introduce an opportunity for reducing opioid-related morbidity and mortality," said Dr. Hattangadi-Gluth. "Of course, it will also be important to identify risks and adverse effects of marijuana, which has not previously been studied on large randomized clinical trials, given its scheduling as a class 1 controlled substance."