Abstract Background The use of cannabis for treating fibromyalgia syndrome (FMS) has not been comprehensively investigated. Thus, we have assessed the efficacy and adverse events (AEs) of short- and long-term medical cannabis (MC) treatment for FMS. Methods Data were obtained from medical reports archived in the pain clinic of Ponderano (Italy; retrospective study). FMS patients, who were resistant to conventional therapy, received licensed MC with various Δ-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) content, as powdered whole flowers (decoction or vaporization) or oil extracts. Demographic and clinical parameters, including Numerical Rating Scale (NRS), Oswestry Disability Index (ODI), Hospital Anxiety and Depression Scale, Widespread Pain Index (WPI),...