Abstract Objectives Medical cannabis formulations with cannabidiol (CBD) and delta-9-tetrahydrocannabinol (THC) are widely used to treat epilepsy. We studied the safety and efficacy of two formulations. Methods We prospectively observed 29 subjects (12 to 46 years old) with treatment-resistant epilepsies (11 Lennox–Gastaut syndrome; 15 with focal or multifocal epilepsy; three generalized epilepsy) were treated with medical cannabis (1THC:20CBD and/or 1THC:50CBD; maximum of 6 mg THC/day) for ≥24 weeks. The primary outcome was change in convulsive seizure frequency from the pre-treatment baseline to the stable optimal dose phase. Results There were no significant differences during treatment on stable maximal doses for convulsive seizure frequency, seizure duration, postictal duration,...