Epidyolex® recently became the first medicinal cannabis product to be listed on the Pharmaceutical Benefits Scheme (PBS). This oral cannabidiol solution is subsidised as adjunctive therapy for severe myoclonic epilepsy in infancy (Dravet syndrome) in patients taking at least two other antiepileptic medicines. Dravet syndrome is a rare and severe form of epilepsy that is often resistant to therapy.

In contrast to delta-9-tetrahydrocannabinol (THC), cannabidiol has a very low affinity for endocannabinoid receptors. Instead, its anticonvulsant effect is thought to be related to the modulation of intracellular calcium and adenosine-mediated signalling. This results in reduced neuronal hyperexcitability and neurotransmission.

The key trial used in the PBS submission for Epidyolex® compared cannabidiol (10mg/kg or 20mg/kg daily) to placebo. All patients were taking at least one other antiepileptic medicine. During the 14-week treatment period, the frequency of convulsive seizures reduced by 48.7% in the low-dose cannabidiol group, 45.7% in the high-dose group, and 26.9% in the placebo group. Total seizure frequency was also reduced (56.4% and 47.3% in the low-dose and high-dose groups, respectively, versus 29.7% in the placebo group).

The most common adverse effects are somnolence, decreased appetite, diarrhoea, pyrexia, fatigue, and vomiting. Epidyolex® may also elevate liver transaminases in a dose-dependent manner, particularly in patients taking sodium valproate. Like any antiepileptic medicine, abrupt discontinuation is not recommended as this may increase the risk of seizures and status epilepticus. The rate of discontinuation in clinical trials was around 10% per day for ten days. However, rapid discontinuation may be appropriate in the setting of serious adverse effects.


  1. Epidyolex® (Cannabidiol) Australian approved product information. Hawthorn East: Chiesi Australia. Approved December 2020.
  2. Miller I, Scheffer IE, Gunning B, Sanchez-Carpintero R, Gil-Nagel A, Perry S, et al. Dose-ranging effect of adjunctive oral cannabidiol vs placebo on convulsive seizure frequency in Dravet syndrome: a randomized clinical trial. JAMA Neurol. 2020; 77(5): 613–21.
  3. Pharmaceutical Benefits Advisory Committee. Epidyolex®: Public Summary Document – July 2020 PBAC Meeting. Canberra: Pharmaceutical Benefits Scheme; 2020.

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