By Carmen Phillips

A series of new studies is putting a spotlight on the growing use of cannabis among people with cancer and some of the trend’s downstream effects.

According to findings from several of the 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 growing popularity of cannabis products among people with cancer has tracked with the increasing number of states that have legalized cannabis for medical use. But research has lagged on whether and which cannabis products are a safe or effective way to help with cancer-related symptoms and treatment-related side effects.

The first-ever clinical guidelines on cannabis use from the America Society of Clinical Oncology (ASCO), published in March 2024, put it bluntly: “Cannabis and/or cannabinoid access and use by adults with cancer has outpaced the science supporting their clinical use.”

Among the most-pressing challenges caused by this scientific evidence deficit, several of the studies found, is that oncologists 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.

“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, MD, who heads the Cherng Family Center for Integrative Oncology at City of Hope in California.

As the legal landscape of medical cannabis continues to change, Dr. Lee continued, providers are only going to be seeing more patients who are using tropical-flavored cannabis gummies or mandarin orange–flavored cannabis tinctures.

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.”

With expanding legality of medical cannabis comes easier access

For years, people with cancer have used cannabis to help manage a range of effects from cancer and other diseases. But until the last decade or so, that practice was almost uniformly illegal in the United States. And because cannabis is what’s known as a schedule 1 drug, it’s still essentially illegal at the federal level.

At the state level, cannabis is now legal for medical use in 14 states and for recreational and medical use in an additional 24 states and the District of Columbia. According to a recent Pew Research Center study, overall, nearly three-quarters of Americans now live in a state where cannabis is legal for medical and/or recreational use.

According to Susanna Ulahannan, MD, an oncologist at the University of Oklahoma’s Stephenson Cancer Center, her younger patients are most likely to use cannabis, often to help with issues like anxiety and trouble sleeping.

Her older patients, however, are more reluctant. And when they do ask about it, Dr. Ulahannan explained, it’s usually when the standard medications she prescribes for problems like pain or lack of appetite aren’t cutting it.

“That’s usually when they bring it up to me,” she said. “‘I’ve tried this and it’s not working. What do you think about trying medical marijuana instead?’”

And in states where cannabis is legal, for those who want to try it, it’s easy to get. According to the Pew study, in fact, there are about 15,000 cannabis dispensaries in the United States.

Is medical cannabis safe for people with cancer?

Access to cannabis is one thing. But whether it is safe to use is another question altogether.

“We absolutely … don’t have a good handle on safety,” said Gary Ellison, PhD, MPH, of NCI’s Division of Cancer Control and Population Sciences, who led one of the JNCI Monographs studies.

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, MD, PhD, medical director of the Comprehensive Center for Pain & Addiction at the University of Arizona Health Sciences.

There are other potential downsides, Dr. Ibrahim continued.

For example, cannabis can be a powerful sedative “and can interact with other medications and be synergistic,” he said. In other words, if somebody is taking another medication that makes them drowsy or less alert, using cannabis at the same time may magnify that drowsiness. And that can increase the risk for things like falls and car accidents, he explained.

But patients don’t always want to hear about the downside, Dr. Ellison said. His and other studies have found that patients generally feel that “the potential benefits [of cannabis] outweigh the risks.”

Explaining to patients the potential harms and lack of evidence around cannabis is a challenge, Dr. Ulahannan agreed. During discussions with patients, she continued, providers are often swimming against a current of wishful thinking or misinformation.

“A lot of patients believe that there’s a more ‘natural way’ to manage symptoms” than by using prescription medications, she said. And in a recent study on cannabis use at her hospital, Dr. Ulahannan said she was surprised to see that many patients who were using cannabis “thought it was helping to treat their cancer.”

Start with what’s known about cannabis and cancer

When it comes to any discussions with patients about cannabis, Dr. Ibrahim said cancer care providers may benefit from understanding the laws on cannabis use in their state and their hospital or academic institutions’ policies on cannabis use.

“You need to know the legal landscape,” he stressed.

Beyond that, he continued, it’s important to think about how to explain to patients how cannabis can affect their body and how it might interact with other medications. “Cannabinoids will affect almost every system [in the body],” he said, including the brain, lungs, and heart.

Dr. Lee recommended that cancer care providers review the ASCO guidelines, as well as read some of the growing number of comprehensive reviews of the biological and physiological effects of cannabis and findings from the few cancer-related clinical studies that have been done.

And Dr. Ulahannan strongly recommended that patients tell their oncologists about any supplements they are taking, including any cannabis products. As the JNCI Monographs study led by Dr. Ellison found, that doesn’t appear to be happening: Only about 20% of patients using cannabis reported having talked to their oncologist about it.

That finding reinforces why it’s important for open communication between clinicians and patients, Dr. Ulahannan said.

“We need to know what our patients are taking,” she said. Even if a provider isn’t fully up to speed on cannabis or some supplement that people are taking because it went viral on social media, having this information can be powerful.

“So maybe you’re not going to reduce [a patient’s] chemo dose because now you know there’s another possible reason for a side effect” they’re experiencing, Dr. Ulahannan said. “Without having that discussion, you wouldn’t know.”

This post was originally published October 16, 2024, by the National Cancer Institute. It is republished with permission.