A two-year-old girl with severe epilepsy is believed to have become the first child in the UK to be prescribed medical cannabis.
For Jorja Emerson the treatment is "the difference between her living and dying", according to her father.
Jorja, who is from Dundonald in County Down, Northern Ireland, suffers up to 30 seizures each day.
She was prescribed the medication at a private hospital in London on Tuesday.
Her father Robin Emerson, a 33-year-old entrepreneur, hopes her treatment will pave the way for other children to gain access to the drug.
"The dam has now broken open," he said.
NHS guidance says a decision to prescribe cannabis should only be made where other treatment options have been exhausted.
Mr Emerson said this made obtaining a prescription difficult.
"I was fearing that this day would never come," he said.
"When medical cannabis was legalised by the home secretary our hopes were raised.
"But we were subsequently left devastated when the NHS guidelines were put out.
"Taken together with recommendations from the Royal College of Physicians (RCP) and the British Paediatric Neurologist Association (BPNA), these guidelines were so tight that hardly anyone would be able to secure a prescription.
"I hope this day paves the way for many other clinicians to have the confidence to prescribe."
NHS guidance says a decision to prescribe cannabis products should only be made where other treatment options have been exhausted.
Although there are other children who are currently receiving medical cannabis treatment in the UK, this is the first time a prescription has been written by a doctor since the drug was rescheduled on November 1, according to campaign group End Our Pain.
Jorja’s treatment will cost her family around £12,000 per year, according to the group.
Her epileptic seizures are caused by rare chromosome deletion and she is the only child with the condition in Northern Ireland or Ireland, according to her father.
The decision to reschedule cannabis products followed several high-profile cases, including those of young epilepsy sufferers Alfie Dingley and Billy Caldwell, whose conditions appeared to be helped by cannabis oil.
The drugs can only be prescribed by a specialist doctor, not a GP, on a case-by-case basis.