Epidyolex, a cannabidiol (CBD) oral medication, has been fast-tracked by the health service in England to be available from 6 January.
Hundreds of children will be among around 2,000 people across the country who it is estimated will benefit from the change in policy.
The drug was recommended for use to treat two rare types of epilepsy – Lennox-Gastaut and Dravet syndromes – back in November.
Clinical trials showed the drug could reduce the number of seizures by up to 40 per cent in some patients.
A change in the law in 2018 had already made it legal for doctors to prescribe medicinal but many have been reluctant to do so, citing a lack of clear guidance on the issue.
Campaign group End Our Pain welcomed the new move and said the announcement would be a boost to families, some of who are currently paying up to £2,000 a month privately for such products.
Millie Hinton, director, said: “They have been pushed to financial breaking point funding the only medicine that gives their children significant seizure control and the quality of life they deserve. Some have actually felt forced to sell their family homes.”
But she added that the NHS should now go further by also providing medication containing Tetrahydrocannabinol (THC) for those with different forms of epilepsy.
“While fast-tracking access to a CBD-only product is a step in the right direction for some desperate families, for those that need the products containing both CBD and THC it’s another false dawn and missed opportunity,” she said. “These families need immediate action to secure NHS prescriptions for the CBD and THC whole plant medical cannabis products.
“It is unbelievably cruel to leave these vulnerable families in such a desperate state.”
Simon Stevens, NHS chief executive, said the service was “committed, through the long term plan, to improving the lives of all those affected by rare diseases.”
He added: “Living with or caring for someone with severe epilepsy is exceptionally challenging, especially as there are so few treatments available for the rare forms of the condition.
“Thousands of people including children will now have access to this treatment, which has the potential to make a real difference.”
Additional reporting by Press Association