The first cannabis-based medicine for childhood epilepsy is expected to be available soon in the UK and the rest of Europe after its UK manufacturer, GW Pharmaceuticals, received the green light from European authorities.

Cambridge-based GW said the European Medicines Agency (EMA) and the European commission had approved Epidyolex for seizures associated with two rare and severe forms of epilepsy, Lennox-Gastaut syndrome (LGS) and Dravet syndrome for patients aged two years and older.

The approval means the medicine – a plant-derived, strawberry-flavoured cannabidiol oral solution that is taken twice a day and lacks the “high” associated with cannabis – can be launched across Europe. Up to 50,000 children and young adults in Europe have one of the two syndromes, including about 10,000 in the UK.

GW’s chief operating officer, Chris Tovey, said the company was in discussions with the UK’s National Institute for Health and Care Excellence (Nice) about making the drug available on the NHS. GW is in parallel discussions in other European countries. The drug is already on the market in the US, where about 15,000 young people have been treated.

Tovey said: “The feedback [in the US] has been incredibly positive.” He said he was very optimistic that Nice would agree to fund Epidyolex on the NHS. “We are hoping for a relatively rapid decision from Nice and we are hoping to make it available for UK patients in the next couple of months.”

However, Nice has turned down Sativex, GW’s cannabis-based medicine for multiple sclerosis, on the grounds of its high price, to the dismay of patients and campaigners.

Justin Gover, GW’s chief executive, said: “The approval of Epidyolex marks a significant milestone, offering patients and their families the first in a new class of epilepsy medicines and the first and only EMA-approved CBD [cannabidiol] medicine to treat two severe and life-threatening forms of childhood-onset epilepsy.”

Many patients with LGS or Dravet suffer multiple seizures a day and do not respond to many of the other available treatments. The two syndromes have high mortality rates and many patients die before they reach their early 20s.

When combined with other anti-epileptic therapies, Epidyolex significantly reduced the frequency of seizures in patients with LGS and Dravet syndrome. The most common side effects include sleepiness, decreased appetite, diarrhoea, pyrexia (fever), fatigue and vomiting.

More than 150 patients have already been treated with the medicine in the UK under compassionate use or as part of an early access programme. “We know the families are desperate,” Tovey said.

A change in UK law last year meant medicinal cannabis can be prescribed legally. The change was made after the mother of Billy Caldwell, who has treatment-resistant epilepsy, publicly defied the authorities to bring cannabis oil into the UK.

Doctors have been reluctant to prescribe cannabis-based medicines in the UK, however, because of the lack of clinical trial evidence of its benefits and safety. This could change after the European approval of Epidyolex.

Isabella Brambilla, the chair of the Dravet Syndrome European Federation, said: “We are very happy that patients will now have access to a much-needed new treatment option, and one routed through a rigorous clinical trials programme and licensed by the EMA.”

Elinor Ben-Menachem, professor of neurology and epilepsy at the University of Gothenburg’s Sahlgren Academy, said: “LGS and Dravet syndrome are two of the most severe and difficult-to-treat forms of childhood-onset epilepsy, with few patients achieving adequate seizure control. The EMA approval of Epidyolex will bring hope to patients and families, with the potential to better control seizures and improve quality of life.”

GW has also filed the drug for approval in Switzerland and Israel. It is conducting further clinical trials on the treatment of other forms of epilepsy with the medicine.