New research indicates that almost half of US adults with breast cancer use cannabis (marijuana and hemp), most commonly alongside cancer treatment to manage symptoms and side effects. However, most patients don’t discuss their use of cannabis with their doctors.

The results published in CANCER, a peer-reviewed journal of the American Cancer Society, are from an anonymous online survey to examine cannabis use among adults who were diagnosed with breast cancer within five years and were members of the Breastcancer.org and Healthline.com online health communities.

The authors said that individuals with cancer often experience pain, fatigue, nausea, and other difficulties that arise from cancer and its treatment. Some turn to cannabis for relief of their symptoms, but many doctors feel that they lack the knowledge needed to discuss cannabis with their patients. 

They added that knowledge is especially important now that cancer is specified as a qualifying condition in nearly all states with medical cannabis programs.

The cannabis plant produces a resin that contains different substances. Some of these may have medicinal value. These substances are called cannabinoids. Two of the main cannabinoids are delta-9-tetrahydrocannabidiol (THC), which is illegal to use in the UK and cannabidiol (CBD), which is legal in the UK.

Most participants believed cannabis products to be safe

Of 612 total participants, 42% reported using cannabis for relief of symptoms, including pain, insomnia, anxiety, stress, and nausea/vomiting. Among those who used cannabis, 75% reported that it was extremely or very helpful at relieving their symptoms.

Other major findings were:

  • Nearly half (49%) of participants who used cannabis believed that medical cannabis can be used to treat cancer itself; however, its effectiveness against cancer is unclear.
  • Among those using cannabis, 79% had used it during treatment, which included systemic therapies, radiation, and surgery.
  • Participants reported using a wide range of different cannabis products known to vary in quality and purity.
  • Half of participants sought information on medical cannabis, and websites and other patients were ranked as the most helpful sources of information. Physicians ranked low on the list.
  • Among those who sought information on cannabis use for medical purposes, most were unsatisfied with the information they received.
  • Most participants believed cannabis products to be safe and were unaware that the safety of many products is untested.

Lead author Marisa Weiss of Breastcancer.org and Lankenau Medical Center near Philadelphia, Pennsylvania, said: “Our study highlights an important opportunity for providers to initiate informed conversations about medical cannabis with their patients, as the evidence shows that many are using medical cannabis without our knowledge or guidance.

“Not knowing whether or not our cancer patients are using cannabis is a major blind spot in our ability to provide optimal care, and as healthcare providers, we need to do a better job of initiating informed conversations about medical cannabis with our patients to make sure their symptoms and side effects are being adequately managed while minimizing the risk of potential adverse effects, treatment interactions, or non-adherence to standard treatments due to misinformation about the use of medical cannabis to treat cancer.”

Dr Weiss added that patients should never use cannabis as an alternative to standard cancer treatment, and clinicians should inform patients about the safe and effective use of cannabis as an adjunct to their cancer treatment plan.