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More than four in 10 breast cancer patients use cannabis, most often to relieve side effects associated with treatment, such as pain, anxiety, nausea, and insomnia, according to a survey study.

Of the Coala-T-Cannabis survey respondents who reported using cannabis, 75% said it was extremely helpful or very helpful in alleviating symptoms, reported Marisa Weiss, MD, of Breastcancer.org and Lankenau Medical Center in Wynnewood, Pennsylvania, and colleagues, writing in .

Furthermore, 57% responded that no other technique was able to provide them with symptom relief. The reported effect of cannabis on symptoms differed significantly by age, with 62% of patients older than 66 reporting a benefit compared with 72% of those ages 50 to 65, and 86% of those younger than 50.

Noting the large proportion of patients who use cannabis during treatment, Weiss and colleagues wrote that "concurrent use of cannabis with anticancer therapies raises important efficacy and safety concerns."

For example, they pointed out that most drug interaction data regarding cannabinoids are based on in vitro studies, and thus the clinical implications of their use during active treatment are unclear.

For the study, members of Breastcancer.org were invited to participate in the survey from Dec. 16, 2019 to Jan. 19, 2020. The survey contained 47 questions designed to gather data on reasons for and timing of cannabis use, sources of cannabis information, perceptions regarding cannabis safety, and dialogue with physicians concerning its use.

Of the 612 survey participants, 257 (42%) reported having used cannabis for medical issues, although just 23% of users said it was for medical purposes only.

Of those who reported cannabis use, 24% reported using it before active treatment began, 79% during treatment, and 54% after the completion of treatment.

Of note, 78% reported they used it for acute, chronic, nerve, joint, and muscle pain; 70% for insomnia; 57% for anxiety; 51% for stress; and 46% for nausea and vomiting.

Interestingly, almost half of cannabis users said that one reason for its use was to treat the cancer itself. While Weiss and colleagues noted that preclinical studies have shown that cannabidiol and tetrahydrocannabinol reduce tumor growth and metastases in animal models of breast cancer, they also pointed out there is no evidence that this benefit translates to humans.

"Despite the high level of interest in cannabis for its possible anticancer effects, at this point the impact of cannabis on breast cancer treatment and breast cancer tumor burden remains unknown," they wrote.

Exactly half of respondents (306) sought information on medical cannabis and were asked to select the most helpful source:

• Websites (22%)
• Family members or friends (18%)
• Non-pharmacist staffers and pharmacists in dispensaries (12% each)
• Other patients with breast cancer (7%)

Of survey participants, 39% discussed cannabis with their physicians, with 28% reporting feeling uncomfortable discussing the topic. Only 4% of respondents selected physicians as the most helpful source of cannabis information.

Moreover, most patients who sought information on cannabis were less than fully satisfied with the information they received, with just 31% reporting being extremely or very satisfied.

Regarding the perceived safety of medical cannabis, 71% of respondents (including 74% of medical cannabis users only) said the benefits of medical cannabis outweigh the risks. However the authors observed that cannabis product safety is a concern, particularly in the case of patients who obtain cannabis from unregulated sources.

"Providers should communicate clearly about the health and safety concerns associated with certain cannabis products and methods of delivery," Weiss and colleagues concluded. "Without these measures, patients may make these decisions without qualified medical guidance, obtain poor-quality cannabis products, and consume them through potentially hazardous delivery methods during various types of cancer therapies."

The authors acknowledged that survey studies are subject to inherent limitations, such as selection and recall bias, and that access to their survey was limited because it was online only and in English.

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