evidence: Cannabis and its derivatives are being used increasingly by patients with cancer, including patients with glioblastoma multiforme (GBM), the most common and aggressive primary brain malignancy. Despite promising preclinical data suggesting potential anti-cancer effects for cannabinoids in GBM, clinical and safety data are lacking. This editorial will discuss a recent Phase 1b trial of nabiximols oromucosal spray in combination with dose-intense temozolomide in patients with recurrent GBM in the context of other relevant findings in this field. [...] A pilot study of intracranial THC administration directly into the surgical cavity of nine patients with recurrent, resected GBM showed a reduction in tumour cell proliferation in the two patients who had further biopsies on the study.6 While this approach appeared tolerable, outcomes in this study remained poor. Anecdotal reports and case series suggesting anti-cancer efficacy of cannabinoid preparations in patients with GBM10 are limited by possible selection bias, other concomitant or recent treatments with proven efficacy, and potential issues with pseudo-progression after such treatments. [...] Likar, R., Koestenberger, M., Stultschnig, M. & Nahler, G. Concomitant treatment of malignant brain tumours with CBD - A case series and review of the literature. Anticancer Res.39, 5797–5801 (2019).