Hundreds of children with severe epilepsy could be prescribed a cannabis-based treatment on the NHS from January.
NHS England said access to Epidyolex, a cannabidiol (CBD) oral solution, has been fast-tracked to be available from January 6.
The cannabis-based medicine was recommended for use on the NHS to treat two rare types of epilepsy, Lennox-Gastaut and Dravet syndromes, for the first time in November.
It will be available for children from the age of two and adults in combination with clobazam, and NHS England estimates around 2,000 people could benefit.
A change in the law in 2018 made it legal for doctors to prescribe medicinal cannabis.
However, many doctors have been reluctant to do so, citing a lack of clear guidance on prescribing and issues over funding for the drugs.
The medicine does not have any of the psychoactive substances which some marijuana products have.
This has led some families to go abroad in search of medicines, with some bringing them into the UK illegally.
Millie Hinton, director of End Our Pain, said the announcement would bring joy to some families but would prolong the suffering of people who need access to products containing CBD and THC.
Some families are paying around £2,000 a month privately for these products, she added.
She 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.
“So, whilst 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.
“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. All these families want for Christmas is for the Government to honour the promises they made to them.”
A review earlier this year looked at the barriers to prescribing cannabis-based medicinal products where it is safe and clinically appropriate.
The National Medical Director and Chief Pharmaceutical Officer for England will write shortly to NHS doctors and pharmacists to clarify the procedure for prescribing unlicensed cannabis-based products where there is an unmet need and it is clinically appropriate.
Around 8,0000 to 9,000 people in the UK suffer Lennox-Gastaut and Dravet syndromes.
Simon Stevens, NHS chief executive, said: “The NHS is committed, through the Long Term Plan, to improving the lives of all those affected by rare diseases.
“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.”
Philip Lee, chief executive at Epilepsy Action, said: “New treatment options for severe epilepsies do not come very often and many families feel they have already been waiting too long to access medicines like Epidyolex.
“This announcement brings much-needed hope and could be life-changing for some.
“However, Epidyolex is not a silver bullet. There is work to be done to collect robust high-quality evidence of the effectiveness of other cannabis-based medicines, including those containing both CBD and THC.
“In the meantime, more people with severe epilepsies should be given the opportunity to access cannabis-based medicines now.”