A cannabis drug used to treat children with epilepsy is too expensive to prescribe even though it reduces patients’ seizures, the UK’s medical advisory body has said.

The National Institute for Health and Care Excellence (Nice) announced today that it would not recommend cannabidiol combined with anti-seizure drug clobazam for the treatment of two types of severe epilepsy, Lennox-Gastaut syndrome and Dravet syndrome.

Draft guidelines say that while there is evidence that cannabis oil reduces the number of seizures children have, the drug is too expensive and its long-term effects are unclear.

Nice was asked by the Department of Health and Social Care to examine whether the cannabis oil drug, used in the United States, should be used in the NHS in England to treat the rare conditions which begin in childhood.

The oil does not contain THC, the psychoactive ingredient that makes cannabis users ‘high’.

Nice’s draft guidance, published today, says that while the oil “reduces the number of the main types of seizures associated with these conditions,” the body had “concerns about the validity of the economic models” of GW Pharma, the company that provides it.

The committee said that GW had not explored the possibility of the oil becoming less effective over time, which is the case with other anti-epileptic medication.