An 11-year-old boy has been given medicinal marijuana on the NHS in what is believed to be the first case of its kind.

Epileptic Billy Caldwell travelled regularly to the US for medication to treat up to 100 seizures a day.

Doctors in the States gave him cannabis oil to help stop the episodes, but when he almost ran out and was unable to go to Los Angeles for more, his desperate mother took him to see his GP.

Dr Brendan O’Hare realised the situation was ‘unique’ and prescribed the CBD oil – a derivative of cannabis that does not contain tetrahydrocannabinol (THC), the illegal psychoactive component of cannabis.

Epileptic Billy Caldwell travelled regularly to the US for medication to treat up to 100 seizures a day

Miss Caldwell, 49, who is Billy’s full-time carer, collected the medicine from her local pharmacy.

Last year, the Medicines and Healthcare products Regulatory Agency allowed the prescription of drugs containing cannabidiol, a component of marijuana, for medical purposes.

Campaigners hope Billy’s prescription will open the door for all patients and GPs who believe in the virtues of medicinal marijuana. 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.’

US research has shown cannabis oil is effective for those with epilepsy. One study of Epidiolex, which is a purified, 99-per-cent oil-based CBD extract from the cannabis plant, showed a 54 per cent decrease in seizures

After eight years in remission, a lesion in Billy’s left temple 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-per-cent oil-based CBD extract from the cannabis plant, showed a 54 per cent decrease in seizures.

Most of its side-effects are moderate, unlike more severe reactions that can be caused by rival drugs. One is thought to be responsible for the ‘severe malformations’ of up to 4,100 children in France.

MPs and drugs policy reform groups hailed the success of Billy’s treatment, and hinted that it could open the door to other British patients in a similar position.

Lib Dem health spokesman Norman Lamb said it was potentially life saving, adding: ‘I don’t think anyone seriously argues against him getting access to treatment that has had such a dramatic impact. There’s lots of evidence, particularly in conditions involving lots of pain, that medical cannabis can be extraordinarily effective.’