Objectives: In patients with cancer, the use of medical cannabis has increased significantly during the recent years. There is evidence that cannabis consumption may affect cognitive performance; however, this potential effect has not been investigated prospectively in patients with cancer to date. We aimed to evaluate the effect of cannabis consumption on cognitive abilities as well as on symptom relief in patients with cancer during chemotherapy treatment.

Patients and methods: A prospective study was carried out on a group of 17 patients on cannabis treatment (case) who were compared with 17 patients not on cannabis treatment (control). Participants completed self-reported questionnaires (the Hospital Anxiety and Depression Scale, Brief Fatigue Inventory, European Organization of Research and Treatment of Cancer core questions on the Quality of Life Questionnaire) and underwent the following neurocognitive tests: Montreal Cognitive Assessment, Digit Symbol Substitution subtest (WAIS III) and Digital-Finger Tapping Test. The evaluation was conducted before the initiation of cannabis consumption and 3 months later during the period of cannabis use.

Results: Improvement in executive functioning was demonstrated in the case group. In aspects of symptoms, improvement in fatigue, appetite and sleep disorder was demonstrated after cannabis consumption. Patients consuming cannabis did not differ from the control group in cognitive functioning over 3 months of use. No significant cognitive decline was observed in either group over time.

Conclusion: These preliminary findings suggest that the short-term use of cannabis during chemotherapy treatment improved disease-related symptoms and did not affect cognitive skills in patients with cancer.