Epidiolex is an oral cannabidiol solution developed by GW Pharmaceuticals. The U.S. Food and Drug Administration (FDA) approved it to treat seizures in patients with Dravet syndrome and Lennox-Gastaut syndrome ages 1 and older.

The treatment also is approved in the EU and Scotland, under the brand name Epidyolex, to treat seizures in patients with Dravet or Lennox-Gastaut syndrome ages 2 or older, in conjunction with clobazam (an anti-epileptic medication).

How does Epidiolex work?

Epidiolex is a plant-derived cannabidiol, a non-psychoactive marijuana extract. This means that it does not have the mind-altering effects that are characteristic of delta (9)-tetrahydrocannabinol (THC).

Doctors have used marijuana derivatives to treat epilepsy since the late 19th century. However, researchers still do not fully understand how cannabidiol works to treat epilepsy. They suggest it may be through the treatment’s ability to interact with many other non-cannabinoid receptors in the brain. 

Epidiolex in clinical trials

An open-label, Phase 1 clinical trial (NCT02286986) compared the safety and tolerability of increasing doses of Epidiolex in patients, ages 2 to 25, with drug-resistant epilepsy. Researchers also aimed to determine changes in the number of seizures that patients experienced during a year. The trial is complete, but results were not made public. 

A Phase 3 clinical trial (NCT02091375), called GWPCARE1, involving 120 patients with Dravet syndrome, ages 2 to 18, was conducted at 23 centers in the U.S. and Europe.

Results showed that a 20 mg per kg body weight dose of Epidiolex for 3.5 months, lowered by half the average number of monthly convulsive seizures compared with the number before treatment (5.9 vs. 12.4). Five percent of those receiving Epidiolex were seizure-free for the duration of the study. However, Epidiolex did not reduce the number of non-convulsive seizures.

Most caregivers of Epidiolex-treated patients (62%) also reported an improvement in at least one category in the clinical global impression (CGI) scale. Only 34% of caregivers of those in the placebo group reported such an improvement. The most common side effects of treatment were fatigue, fever, vomiting, diarrhea, sleepiness, and abnormal liver enzyme test results. These were recorded in 93% of patients taking Epidiolex. A majority of those (89%) were of mild-to-moderate severity. Researchers published the findings in The New England Journal of Medicine.  

Another Phase 3 clinical trial (NCT02224703), GWPCARE2, conducted sites in the U.S. and in the Netherlands, assessed the safety and effectiveness of Epidiolex in children and young adults with Dravet syndrome. The trial compared a high dose (20 mg/kg per day) and a low dose (10 mg/kg per day) of Epidiolex to a placebo. It measured changes in the number of convulsive seizures from the study’s start until after 14 weeks of treatment.  

Researchers presented trial results at the 2019 American Academy of Neurology (AAN) Annual Meeting. Of the 199 children enrolled, 46% of those in the high-dose group and 49% in the low-dose group saw a reduction in convulsive seizures. This percentage was 27% in the placebo group. The incidence of adverse events was similar across all groups, at around 90%. The most common were less appetite, diarrhea, excessive sleepiness, fever, and fatigue.

An open-label, Phase 3 extension trial (NCT02224573), GWPCARE5, was conducted in a reported 681 children and young adults with Dravet or Lennox-Gastaut syndrome who took part in earlier studies. Its aim was to record side effects, changes in seizure symptoms, and overall improvements in patients’ quality of life over years of Epidiolex use. A three-year interim analysis indicated that 315 Dravet syndrome patients enrolled in GWPCARE5. The report showed that the long-term use of Epidiolex continued to reduce the frequency of seizures without new safety concerns.

Additional information

Epidiolex had the largest expanded access program (also known as a compassionate use program) in epilepsy, a program that allows patients with potentially life-threatening conditions to gain access to treatments not available outside of clinical trials. Through this program, more than 1,100 patients were able to receive Epidiolex treatment.

Greenwich Biosciences, a subsidiary of GW Pharmaceuticals, markets this medication.


Last updated: Oct. 16, 202o


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