Epidiolex is an oral cannabidiol medication developed by GW Pharmaceuticals and approved in the U.S. to treat seizures in patients with Lennox-Gastaut syndrome and Dravet syndrome, ages 1 and older. The European Commission and the Scottish Medical Council also approved Epidiolex for patients ages 2 and older, under the brand name Epidyolex, as an add-on therapy to clobazam.

How does Epidiolex work?

Epidiolex is an oral cannabidiol solution derived from the cannabis or marijuana plant. Cannabidiol is a non-psychoactive extract from marijuana. This means that Epidiolex does not have the characteristic “high” effect of marijuana.

Doctors have used cannabis products to treat seizures for centuries. However, their exact mechanism of action is unclear. A seizure is the result of abnormal brain activity. The endocannabinoid system (ECS) of the brain and spinal cord plays a vital role in modulating several essential neurological functions, including the release of hormones and the activity of nerve cells. Cannabidiol may exert an anti-seizure effect by indirectly regulating ECS activity. It may also modulate the levels of calcium, which is essential for the proper communication between nerve cells.

Epidiolex in clinical trials

Researchers have evaluated Epidiolex for the treatment of seizures associated with Lennox-Gastaut syndrome and Dravet syndrome. The key studies they conducted in Lennox-Gastaut syndrome patients are indicated below.

An international Phase 3 study (NCT02224560), called GWPCARE3, compared the safety and efficacy of Epidiolex versus a placebo in patients, ages 2 to 55. A total of 225 patients enrolled in this study. Researchers randomly grouped patients and gave them either 20 mg/kg of Epidiolex, 10 mg/kg of Epidiolex, or a placebo daily for 14 weeks. The median reduction in atonic seizure frequency during the treatment period was 41.9% in patients taking 20 mg/kg of Epidiolex, 37.2% in those taking 10 mg/kg of Epidiolex, and 17.2% in those taking the placebo. Researchers published these results in The New England Journal of Medicine. Adverse events were most common in the highest Epidiolex dose group and included sleepiness, diarrhea, and low appetite.

A Phase 3 multicenter study (NCT02224690), GWPCARE4 evaluated the efficacy of Epidiolex as an add-on therapy for atonic seizures in patients who did not respond to other treatments alone. A total of 171 patients, ages 2 to 55, took part. They received either 20 mg/kg of oral Epidiolex or a placebo daily for 14 weeks. The frequency of atonic seizures was reduced by a median of 43.9% in the Epidiolex group compared to 21.8% in the placebo group in a month. These results appeared in the medical journal The Lancet. Diarrhea, low appetite, fever, sleepiness, and vomiting were the most common side effects.

A Phase 3 extension study (NCT02224573), GWPCARE5, which included participants from previous placebo-controlled studies of Epidiolex, recruited 681 patients with Lennox-Gastaut syndrome or Dravet syndrome. The follow-up duration for the study is five years. Overall, 366 out of 368 patients joined the extension study. The results after three years showed a reduction of 48%–68% in total seizures, indicating that long-term use of Epidiolex continues to reduce seizures without new safety concerns.

Ongoing clinical trials

A new Phase 4 study (NCT04133480) will assess the impact of Epidiolex on the cognitive abilities of children with Lennox-Gastaut syndrome, ages 3 to 10. The 30-week open-label study aims to enroll a total of 116 patients. For the first seven days, participants will receive 5 mg/kg of oral Epidiolex. This dose will be increased and maintained at 10 mg/kg daily for the rest of the study. The investigators may further increase the dosage to 20 mg/kg daily if clinically warranted. The National Institutes of Health Toolbox Cognition Battery will be used to assess cognitive function.


Last updated: Oct. 16, 2020


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