Cannabidiol for use in the treatment of epilepsy, wherein the epilepsy is a treatment-resistant epilepsy (TRE), and wherein the TRE is Tuberous Sclerosis complex (TSC), is provided. Preferably the TSC is characterised by both complex partial seizures and generalised seizures or primarily by complex partial seizures. Preferably the CBD is used in combination with one or more concomitant anti-epileptic drugs (AED) which may be selected from the group consisting of clobazam, levetiracetam, topiramate, stiripentol, phenobarbital, lacsamide, valproic acid, zonisamide, perampanel and fosphenytoin, wherein the dose of anti-epileptic drug/s that is/are used in combination with the CBD is reduced. Preferably the CBD is present as a highly purified extract which comprises at least 98% (w/w) CBD. Preferably the extract further comprises up to 1% CBDV (cannabidivarin) and less than 0.15% THC (tetrahydrocannabinol). Preferably the dose of CBD is from 5mg/kg/day to 25mg/kg/day.
