More cancer patients are using cannabis products to help manage the symptoms of their disease or side effects caused by treatment. According to several studies, anywhere from about 20% to 40% of people being treated for cancer use cannabis or cannabinoids—often broadly referred to as medical marijuana—to help manage side effects like nausea, pain, sleeplessness, anxiety, and stress.
The American Society of Clinical Oncology (ASCO), published in March 2024,(1) the first-ever clinical guidelines on cannabis use. The guideline provides strategies for open, nonjudgmental communication and also discusses evidence regarding cannabis and cannabinoids as cancer-directed therapy and for managing cancer symptoms and treatment side effects. It recommends clinicians inquire their patients routinely and nonjudgmentally about cannabis use (or consideration of cannabis use), and either guide care or direct adults with cancer to appropriate resources. The full guideline offers suggestions for taking a cannabis and/or cannabinoid history.
Several studies have found that clinicians and other cancer care providers feel ill-equipped to talk with their patients about medical cannabis. In one of the studies, for example, although nearly 40% of the oncologists and oncology nurses surveyed said they were comfortable offering guidance to patients on cannabis use, only about 13% said they felt that they were knowledgeable about cannabis. The studies, all funded by NCI and conducted at NCI-Designated Cancer Centers, were collectively published in August in JNCI Monographs.(2) “Patients are highly interested in cannabis” to help them deal with cancer’s physical and mental fallout, said the study’s lead investigator, Richard T. Lee, M.D., who heads the Cherng Family Center for Integrative Oncology at City of Hope in California. So even without reliable evidence, it’s important to ask patients if they are using cannabis products and for what purpose, he said. And for now, “treat it like any other medication, and explain that it has potential harms and potential benefits.”
Common side effects of tetrahydrocannabinol (THC)-based products include dizziness, mild confusion, dry mouth, and fatigue; more serious side effects include tachycardia, orthostatic hypotension, severe confusion, and paranoia. To minimize adverse effects from THC-based products, particularly in older adults and in those naïve to cannabis and/or cannabinoids, such products should be started at a low dose and titrated slowly.
One of the biggest concerns is whether cannabis products might interfere with patients’ cancer treatments. For example, results from some small studies have suggested that cannabis can make immunotherapy treatments less effective. Indeed, it’s known that cannabis can suppress the immune system, particularly when used over a long period, explained Mohab Ibrahim, M.D., Ph.D., medical director of the Comprehensive Center for Pain & Addiction at the University of Arizona Health Sciences.
Several ongoing studies are testing synthetic drugs that chemically are nearly identical to the components in cannabis, like THC, that are thought to help with side effects like nausea and pain. Two such drugs, dronabinol and nabilone, are already approved by the Food and Drug Administration to treat cancer-related pain.
