The New York Times will report tomorrow that an experimental drug derived from marijuana has succeeded in reducing epileptic seizures in its first major clinical trial, the product’s developer announced on Monday, a finding that could lend credence to the medical marijuana movement.

The developer, GW Pharmaceuticals, Epidiolex, achieved the main goal of the trial, reducing convulsive seizures when compared with a placebo in patients with Dravet syndrome, a rare form of epilepsy. GW shares more than doubled on Monday.
If Epidiolex wins regulatory approval, it would be the first prescription drug in the United States that is extracted from marijuana. The drug is a liquid containing cannabidiol, a component of marijuana that does not make people high.
As many as 30 percent of the nearly 500,000 American children with epilepsy are not sufficiently helped by existing drugs, according to GW. Parents of some of these children have been flocking to try marijuana extracts, prepared by medical marijuana dispensaries.
A number of states, in response to pressure from these parents, have passed or considered legislation to make it easier to obtain marijuana-based products. And some families have become “marijuana refugees,” moving to Colorado where it has been easier to obtain a particular extract, known as Charlotte’s Web, after the girl who first used it to control seizures.

Hundreds of other children and young adults have been using Epidiolex outside of clinical trials, under programs that allow desperate patients to use experimental drugs.

The company said that for the patients who received Epidiolex, the frequency of convulsive seizures fell by 39 percent during the 14-week treatment period, compared with a four-week period just before the treatment started. For those getting the placebo, the reduction was 13 percent. The difference between the two groups was statistically significant.

Eight patients getting Epidiolex and one getting the placebo withdrew from the trial because of side effects. Major side effects included drowsiness,diarrhea, decreased appetite, fatigue, fever, vomiting and upper respiratory infection. But GW said that over all, the drug was well tolerated.

One caution is that the full details of the study were not released; the company said they would be presented at a medical conference.

If it wins regulatory approval, Epidiolex would be the first prescription drug in the United States that is extracted from marijuana.via GW Pharmaceuticals

GW, which is based in London, said Monday that it would meet with the Food and Drug Administration to see if Epidiolex could be approved based on this single study. It is expecting the results of another trial for Dravet syndrome later this year, and the results of two trials in another form of epilepsy, Lennox-Gastaut.

There are no drugs approved specifically for Dravet syndrome, which typically starts in infancy and affects about 5,000 children in the United States, according to the company. It is not yet known if Epidiolex can help with the walking problems and intellectual disability that can come with Dravet, Dr. Devinsky said.

American depositary receipts of GW closed up about 120 percent on Monday. The company, which specializes in cannabis-based pharmaceuticals, already sells Sativex to treat spasticity associated with multiple sclerosis. It is approved in many countries, though not the United States.

While Epidiolex could be the first prescription drug in the United States extracted from marijuana, two drugs already on the market, dronabinol and nabilone, are synthetic chemicals either similar to or identical to delta-9 THC, the component of marijuana that produces the highs.

Those drugs are approved to treat nausea and vomiting caused by cancer chemotherapy. Dronabinol is also approved to treat weight and appetite loss in patients with AIDS.

GW executives say that an approved pharmaceutical should be favored by doctors and patients because the other medical marijuana products have not gone through the same rigorous vetting.

A study last year by researchers at Johns Hopkins University and elsewhere found that medical marijuana products rarely contained the amount of ingredients stated in their labels.The F.D.A. has been sending warning letters to some companies, many of them selling hemp oil, saying that they are illegally marketing their products as drugs and that cannabidiol cannot be sold as a dietary supplement because it is being studied for use as a drug.

But even if Epidiolex wins approval, some parents might stick with other products, either because they do not want to disrupt their child’s treatment or they prefer a fuller plant extract to the single ingredient in Epidiolex.

“My kid’s stable. I’m not touching it,” said Allison Ray Benavides, whose 6-year-old son, Robby, is using Charlotte’s Web, to which a little of the psychoactive component THC is added.

Robby used to have 15 to 25 seizures a day, even while taking the approved drug Depakote, and had to wear a helmet all day to protect his head from falls, said Ms. Ray Benavides, a medical social worker in San Diego.

Since starting on Charlotte’s Web more two years ago, while continuing with Depakote, he has had a total of only five seizures.

“I don’t need a double-blind placebo-controlled study to know something,” she said, while nonetheless welcoming the Epidiolex trial results.

Analysts expect Epidiolex to cost $2,500 to $5,000 a month, which would be more expensive than some of the medical marijuana products, which cost from about $100 to more than $1,000 per month. However, Epidiolex might be covered by insurance, unlike the other products.