Epileptic Billy Caldwell had been travelling to the US for medication to treat up to 100 life threatening seizures a day.
Doctors over the pond in Los Angeles gave him cannabis oil to help stop the episodes, but when he returned his supply soon ran out.
Unable to make the return trip his mum and full-time carer Charlotte, 49, took him to see his local GP desperate to find more CBD oil.
Dr Brendan O’Hare realised the situation was “unique” and prescribed the oil – a derivative of cannabis that does not contain tetrahydrocannabinol (THC), the illegal psychoactive component of cannabis.
Miss Caldwell 5then collected the medicine from her local pharmacy.
Campaigners now hope Billy’s prescription will open the door for all patients and GPs who believe in the virtues of the medicinal drug.
Miss Caldwell, who lives with her son in Castlederg, Northern Ireland, told the Daily Telegraph: “With just a few days’ doses of Billy’s US medication left, I was getting desperate.
“In the end I called my GP and gave him all our paperwork and he said he’d prescribe the medicinal cannabis for Billy, and that’s exactly what he has done.
“We went down to our surgery and picked it up. It was as simple as that.”
Miss Caldwell, who campaigns for children to receive the treatment, added: “It’s a huge step forward. It’s an alternative treatment and it’s worked out well for Billy.”
Last year, the Medicines and Healthcare products Regulatory Agency allowed the prescription of drugs containing cannabidiol, a component of marijuana, for medical purposes.
Billy was in remission for eight years when a lesion in his left temple devastatingly brought back his seizures.
The oil was helping to reduce the damage and had stopped the seizures for three months.
Dr O’Hare said he supplied a prescription because Billy faced a “crisis”, adding: “Whatever the rights and wrongs, we had a child who had benefitted and the child’s welfare was paramount. On that basis I issued a prescription.
“This was not to open the floodgates for others, it is a one-off.”
US research has shown cannabis oil is effective for those with epilepsy. One study of Epidiolex, which is a purified, 99% oil-based CBD extract from the cannabis plant, showed a 54% decrease in seizures.