Cannabis and Radiation Therapy: A Scoping Review of Human Clinical Trials

It is estimated that at least 20% of Canadian patients with cancer use cannabis to alleviate symptoms of their disease and/or cope with the side effects of their treatment. Most patients want to learn more about cannabis from their healthcare team, but most oncology professionals feel too uninformed to make recommendations. The purpose of this scoping review was to address this oncology professionals' knowledge gap, by summarizing the literature on evaluations of the benefits and harms of cannabis use before, during, or after radiation therapy (RT).

A literature search was performed in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses extension for Scoping Reviews guidelines, using multiple electronic databases and combinations of key terms. To be included, studies must address the use of cannabis in patients undergoing RT. In vitro and in vivo evaluations, reviews, and editorials were excluded. Eligible full text manuscripts were then subjected to a formal risk of bias assessment using the Cochrane RoB 2.0 or ROBINS-I frameworks.

A total of 48 records were identified, and 8 articles were included after vetting. These 8 studies suggest that the use of cannabinoids may calm anxious patients about to start RT, reduce nausea and vomiting consistent with the contemporary standard of care, reduce the symptoms of relapse for patients with glioma, and provide symptom relief >3 years after head and neck RT but not during or immediately. Six of these studies contained a high risk of bias (eg lack of randomization, poor blinding, and subjective outcome assessments). Most studies reported mild episodes of drowsiness and dry mouth with Δ⁹tetrahydrocannabinol, but substantial rates of dizziness, fatigue, and disorientation were also seen. It is important to note that these studies did not measure the impact of long-term cannabis consumption.

The existing body of literature evaluating the use of cannabinoids by patients undergoing RT is very limited. Well-designed randomized controlled trials are urgently needed, which address the significant design flaws of previous studies and evaluate the impact of phytocannabinoids in patients undergoing RT.