Many cancer patients experience pain, nausea and fatigue associated with their condition and its treatment, and some use cannabis — marijuana — to relieve their symptoms and side effects. And though cancer is a qualifying condition in almost all states where medical cannabis is legal, many physicians say they lack the knowledge to discuss the use of cannabis with their patients.

Researchers led by a team from Lankenau Medical Center in Pennsylvania and the Lankenau Institute for Medical Research recently conducted an online survey of more than 600 breast cancer patients about their use of medical cannabis. More than 40 percent of respondents said they used cannabis to manage symptoms. And almost 80 percent of cannabis users indicated that they took it during treatment such as chemotherapy and radiation, and following surgery. However, only 39 percent reported discussing their cannabis use with their physician.

About 75 percent of patients who used cannabis said it was very helpful or extremely helpful for relieving their symptoms.

“The study highlights an important opportunity for providers to initiate informed conversations about medical cannabis with their patients,” said Marisa Weiss, lead author on the study. Patients need to realize that keeping their providers in the dark about their cannabis use is a serious omission and likely to result in less than optimal care, Weiss, the director of breast radiation oncology at Lankenau Medical Center, added. “As clinicians, we need to make sure patients’ symptoms and side effects are being adequately managed, while minimizing the risks of adverse effects, treatment interactions, and non-adherence because of misinformation about medical cannabis.”

Half of all respondents had sought information on medical cannabis. They said websites and other breast cancer patients were the most helpful sources. Only four percent said a physician was the most helpful. Most respondents who sought information on medical cannabis were not satisfied with the information they received. But 25 percent said they were very satisfied with the information, 44 percent were somewhat satisfied and six percent were unsatisfied.

About 75 percent of patients who used cannabis said it was very helpful or extremely helpful for relieving their symptoms. Almost 60 percent indicated they had found no other remedy for their symptoms.

Cannabis users reported trying a variety of cannabis products that differed in purity and quality. Almost half of respondents believed that medical cannabis can treat the cancer itself, although the exact mechanism by which it did so was not clear.

Almost 80 percent of cancer patients who used cannabis did so during treatment such as chemotherapy and radiation, and following surgery, but less than half of them reported discussing their cannabis use with their physicians.

Most of the patients surveyed believed cannabis products to be safe and were unaware that the safety of these products is untested. More than 70 percent of respondents said they believed cannabis products should be considered plant-based medicine, that natural products were better than chemicals, and that the benefits of cannabis outweighed the risks.

Many did not know the difference between cannabidiol (CBD) and tetrahydrocannabinol (THC) derived from hemp plants and those derived from marijuana (40 percent of cannabis users and 60 percent of nonusers) or the difference between CBD and THC (18 percent of users and 46 percent of nonusers).

Studies have shown THC relieves nausea and pain, but more research about the effectiveness of CBD for these purposes is needed, the researchers say.

The study is published in Cancer.