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CBD was shown to have anti-seizure activity based on in vitro and in vivo models. However, several reports of small series or case reports of the use of cannabis extracts in epilepsy yielded contradictory results and the efficacy of cannabis use in patients with epilepsy have also been inconclusive. In 2013, the first Phase 1 trial for a purified form of CBD (Epidiolex/Epidyolex; >99% CBD), developed by GW Pharma, showed some efficacy signals and subsequently, a comprehensive program on the efficacy and tolerability of this compound for the treatment of drug-resistant epilepsies was initiated. Results of these trials led to the FDA and EMA approval respectively in 2018 and 2019 for the treatment of seizures associated with two rare epilepsies: Lennox-Gastaut syndrome (LGS) or Dravet syndrome (DS) in patients two years of age and older. Thus, CBD became the first FDA-approved purified drug substance derived from cannabis and also the first FDA-approved drug for the treatment of seizures in DS. We detail the clinical studies using purified CBD (Epidiolex/Epidyolex), including the first open interventional exploratory study and Randomized Control Ttrials for DS and LGS.