Epidiolex (GWP42003-P) is an investigative, oral cannabidiol solution developed by GW Pharmaceuticals for patients with treatment-resistant forms of epilepsy including Dravet syndrome, Lennox-Gastaut syndrome, tuberous sclerosis complex, and infantile spasms.

How Epidiolex works

Epidiolex is a plant-derived cannabidiol, a non-psychoactive marijuana extract, meaning that it does not have the mind-altering effects that are characteristic of delta (9)-tetrahydrocannabinol (THC), the main psychoactive component of marijuana that gets people “high.”

While marijuana derivatives have been used to treat epilepsy since the late 19th century, modern-day researchers still do not fully understand how cannabidiol works to relieve epilepsy, and hypothesize that it may be due to its ability to interact with many other non-cannabinoid receptors in the brain. (The brain has a natural endocannabinoid system with cannabinoid receptors that can respond to CBD and THC).

Epidiolex in clinical trials

An open-label, Phase 1 clinical trial (NCT02286986) is currently ongoing to compare the safety and tolerability of increasing doses of Epidiolex given to patients ages 2 to 19 with a diagnosis of drug-resistant epilepsy.

Researchers also aim to determine changes in the number of seizures experienced over a year. The trial is active but no longer recruiting participants. It is being conducted at the University of Utah and is expected to be completed in December 2018.

A Phase 2 clinical trial (NCT02091206) compared oral Epidiolex doses of 5 mg/kg, 10 mg/kg, and 20 mg/kg to placebo for 21 days to patients ages 4 to 10. The trial’s goals were to determine any side effects and to measure blood cannabidiol concentrations at various times after taking the medication. At the end of the 21-day period, trial results were reviewed by an independent data safety monitoring committee, but no results were made available.

Results from a Phase 3 clinical trial (NCT02091375) conducted at 23 centers in the U.S. and Europe found that 120 children and young adults ages 2 to 19 who were given 20 mg per kg body weight of Epidiolex for three and a half months had half the average number of convulsive seizures in a month (from 12.4 to 5.9) compared to the number they experienced before treatment.

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. Sixty-two percent of caregivers of those who received Epidiolex noticed an improvement of at least one category in the Caregiver Global Impression (CGI) scale, compared to the 34 percent of caregivers of those in the placebo group.

The most common side effects were fatigue, fever, vomiting, diarrhea, sleepiness, and abnormal liver enzyme tests, recorded in 93 percent of patients taking Epidiolex. A majority of these (89 percent) were of mild to moderate severity. The findings from this trial were published in the medical journal The New England Journal of Medicine.  

Another Phase 3 clinical trial (NCT02224703) began in 2015 and is looking into the safety and effectiveness of Epidiolex in children and young adults with Dravet syndrome. The trial aims to compare a high and low dose of Epidiolex to placebo in terms of their abilities to reduce the number of seizures within a three-and-a-half month treatment period. The trial is taking place at clinical sites in the U.S. and in the Netherlands.

An open-label, Phase 3 extension trial (NCT02224573) is currently underway. This trial aims to record side effects, improvements in seizure symptoms, and overall improvements in quality of life in patients who were in the previous Phase 1, 2 and 3 clinical trials of Epidiolex. The trial is enrolling by invitation and is expected to end in June 2019.

Additional information

Epidiolex was granted orphan drug status by the U.S. Food and Drug Administration and the European Medicines Agency. The FDA has also accepted for review a new drug application (NDA) for Epidiolex. The investigational therapy also has priority review status, so the review of the NDA is expected to take place more rapidly and the outcome announced in June 2018.

In February 2018, the EMA accepted for review a marketing authorization application for Epidiolex, a process that would allow the medication to be approved and marketed in all E.U. member states.  The outcome of this review is expected in early 2019.

Epidiolex also has 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 treatment not available outside of clinical trials.

Under this program, over 1,100 patients were able to receive Epidiolex treatment. The medication is provided free of charge by Greenwich Biosciences, a subsidiary of GW Pharmaceuticals


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