To the novice investor, GW Pharmaceuticals might look like just another trend-chasing medical marijuana startup jumping on the cannabis bandwagon.

Cannabidiol (CBD) products—the non-psychoactive compound derived from the hemp plant—have exploded in popularity and are showing up in everything from shampoo to coffee in shops across the U.S. and U.K.

But GW has something none of its competitors have: approval from regulators to sell its products as prescription medicines.

On Sept. 24, the Nasdaq-listed company was given the green light by the European Commission to market Epidyolex, its treatment for severe forms of childhood epilepsy throughout the European Union.

“It is a historic moment for the company,” said Justin Gover who has been GW’s chief executive since 1999.

“It has taken 20 years to reach this point. We have helped spur on the science behind cannabinoids and provided credibility to regulators,” he adds.

The EU’s approval opens the way for a lucrative new revenue stream from Europe. More markets are set to follow. Gover says GW is actively exploring opportunities in Japan, Australia and Israel for further expansion.

For now, the U.S. will continue to provide the lion’s share of revenues and growth. Launched there in late 2018 under the name of Epidiolex, more than 12,000 patients have so far received the drug. Sales totaled $68.4 million in the second quarter, more than double the level reached in the previous quarter and surpassing Wall Street expectations.

While GW is listed in New York, its roots remain firmly in the U.K., where it was founded in 1998. It still grows its own cannabis and turns the plant into pharmaceutical-grade medicines developed and manufactured at its facilities in England.

It hasn’t been an easy journey. Twenty years ago, the idea of making medicines from cannabis was a lonely pursuit. GW had to secure a special license from the U.K. Home Office to grow the illegal drug for research and for years the location of its R&D and manufacturing facilities were kept top-secret.

After listing on London’s junior Aim market in 2001, the stock struggled to attract U.K. investors who were wary of the biotech sector which typically has long development cycles and high failure rates. Frustrated, Gover turned to the U.S. in search of fresh capital.

“We faced a challenge raising the money in London. In the U.S., the investor base was deep and wide enough to sustain the high-risk and failure which is inherent to our business,” he says.

GW has since raised about $1.5bn on Nasdaq to finance commercialization of Epidiolex.

Investors have been rewarded with a tenfold increase in its market capitalization since the initial public offering. But the stock has fallen from its all-time high in May, reflecting a wider correction in cannabis-related assets after a long boom.

Frustratingly, after years dealing with a combination of skepticism and disinterest, GW has suddenly found itself in a crowded field as cannabis laws have begun to liberalize on both sides of the Atlantic and the medical potential of marijuana is increasingly accepted.

Gover is confident GW can maintain its lead. “They [new entrants] have to catch up on 15 years of clinical research and expertise we have developed,” he says.

As well as Epidiolex, GW has a cannabis-based treatment for the symptoms of multiple sclerosis, called Sativex, approved in more than 25 countries, although not yet the U.S.

Govers says GW is also pursuing research and development in further pediatric neurological conditions, including autism.

But GW’s immediate priority is successful commercialization of Epidiolex. Demand is high for new treatment options for children and young people suffering from severe and sometimes life-threatening forms of epilepsy. Epidiolex is approved for the treatment of two specific rare types of the disease: Lennox-Gastaut syndrome and Dravet syndrome.

Uptake has been strong in the U.S. but there are additional barriers in Europe from the gatekeepers who control spending in the region’s public-funded health care systems.

GW is currently in talks with the National Institute for Health and Care Excellence (NICE)—the body which decides if treatments offer value for money for England’s National Health Service—about funding Epidyolex.

NICE turned down Sativex because of its high price but GW is hopeful of a recommendation for Epidyolex, which, in clinical trials, significantly reduced the frequency of seizures in patients when combined with other anti-epilepsy medicines.

Epidiolex has an average price of about $32,500 per patient, a year in the US. Like all medicines, the price will be lower in Europe, where public health systems exert strong bargaining power.

The product is a purified form of CBD and, unlike unlicensed medical cannabis products, it comes in highly concentrated, standardized doses backed by evidence of its safety and efficacy from randomized, placebo-controlled clinical trials.

Some CBD oils containing Tetrahydrocannabinol (THC), the cannabis compound that makes people high, are also being developed for medicinal use. But the regulatory hurdles for these products are higher in most countries as THC remains illegal.

As long as regulators demand the same standards of evidence for cannabis-based medicines as they do for other pharmaceuticals, GW’s lead will prove hard to close. Rigorous clinical trials typically take several years and tens or even hundreds of millions of dollars to complete.

“This is not a cannabis stock,” says Gover. “We are a biotech company with very specific claims and very specific products.”