Cannabis use among Danish patients with cancer: a cross-sectional survey of sociodemographic traits, quality of life, and patient experiences

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Abstract
Purpose
Patients with cancer are using cannabis for self-treatment. The reasons, experienced effects, and prevalence of use are unknown in the European general oncological population.

Methods
Adult patients with cancer attending outpatient oncology clinics were invited to participate in a cross-sectional survey. The questionnaire consisted of sociodemographic questions, validated scales on quality of life, neuropathy, anxiety and depression as well as questions regarding use of cannabis.

Results
The overall response rate was 83% (2839 patients) and 13% of patients were using or had used cannabis during their treatment. Rate of use was higher in smokers (19% vs 11%, p adjusted 0.002), in patients in active cancer treatment (14% vs 10%, p adjusted = 0.02), and in patients with depression (19% vs 11%, adjusted p = 0.002). Cannabis use was also correlated with lower quality of life (EORTC C30 SumScore mean diff. =  − 7.61, 95% CI = [− 9.69; − 5.53]).

In total, 77% of users experienced at least one positive effect of cannabis, 18% experienced no effect, and 5% experienced other effects. At least one side effect was experienced by 33% of users. Management of pain and nausea were the primary reasons for initiating cannabis use (39% for both). Less nausea and better sleep were the most common effects experienced (26% for both). Oils for oral use were the most common route of administration (88%).

Conclusion
Cannabis use among patients with cancer is prevalent and correlated with worse quality of life. Patients report using cannabis for symptom management and many experience relief of their symptoms. However, one third of patients experienced side effects.