Two cannabis-based medicines used to treat epilepsy and multiple sclerosis, have been approved for use by the NHS in England.
It follows new guidelines from the drugs advisory body NICE, which looked at products for several conditions.
Charities have welcomed the move, although some campaigners who have been fighting for access to the drugs have said it does not go far enough.
Both medicines were developed in the UK, where they are also grown.
Doctors will be able to prescribe Epidyolex, for children with two types of severe epilepsy â€“ Lennox Gastaut syndrome and Dravet syndrome â€“ which can cause multiple seizures a day.
Clinical trials have shown the oral solution, which contains cannabidiol (CBD), could reduce the number of seizures by up to 40% in some children.
Epidyolex was approved for use in Europe in September, but in draft guidance, NICE initially said it was not value for money.
It costs between Â£5,000 and Â£10,000 per patient each year â€“ but the manufacturer, GW Pharmaceuticals, has agreed a lower discounted price with the NHS.
It is estimated there are 3,000 people with Dravet and 5,000 with Lennox Gastaut syndrome in England.
The drug does not contain the main psychoactive component of cannabis, THC.
Decisions on drug availability are devolved around the UK, but the NICE guidance should also apply in Wales and Northern Ireland. Scotland may follow suit next year.
The other treatment, Sativex, is a mouth spray that contains a mix of THC and CBD.
It has been approved for treating muscle stiffness and spasms, known as spasticity, in multiple sclerosis. But doctors will not be allowed to prescribe it to treat pain.
It was the first cannabis-based medicine to be licensed in the UK after clinical trials and has been available on the NHS in Wales since 2014. It costs around Â£2,000 a year per patient.
Back then, regulators in England said it was not cost-effective, but now that decision has been reversed. It should also be available in Northern Ireland.