A GP, who prescribed medicinal cannabis to a County Tyrone boy to treat uncontrollable epilepsy, has been told he cannot do so again.
In 2017, 12-year-old Billy Caldwell became the first person in the UK to receive the NHS prescription.
Dr Brendan O'Hare said there is an "ethical issue" in not allowing Billy to have medicinal cannabis.
His mother, Charlotte Caldwell, said his seizures had dramatically reduced while taking the cannabis oil.
Last week when she went to renew the prescription she was told it would not be possible.
After initially prescribing the medicinal cannabis, Dr O'Hare had been told by the Department of Health and the health board last year he should not continue to do so.
The Department of Health in Northern Ireland said it did not comment on individual cases, but added that Cannabis is a Class B controlled drug and has not yet been licensed in the UK as a medicine.
"However, an application made by a specialist clinician based in the UK to prescribe a Schedule 1 controlled drug on the basis of relevant medical and scientific evidence and guidance may be considered within existing legislative provisions and appropriate clinical supervision arrangements.
"No such clinically supported applications have been received by the department," it confirmed.
Dr O'Hare reiterated that his initial prescription was "not a support of the irresponsible use of products for ailments for which there is no evidence".
But he said in this specific case, this child has benefited and "the reduction in his fit frequency is huge".
"This is not to open the floodgates for products, it's about one individual child," he added
Billy Caldwell was first given the treatment in the USA by an epilepsy expert. His mother told BBC Radio Five Live that until that point Billy was having up to 100 seizures a day.
Ms Caldwell said the effect on her son was "miraculous".
"For Billy it's controlling his life-threatening seizures. That is what a small bottle is doing for him."
CBD and Tetrahydrocannabinol (THC) are two types of cannabinoids found naturally in the resin of the marijuana plant.
Unlike THC, pure CBD oil is not a psycho-active ingredient associated with the "high" in marijuana.
There is no restriction on the personal use of CBD oil.
However, the Medicines and Healthcare products Regulatory Agency (MHRA) is of the opinion that CBD products, used for a medical purpose, are medicines.
CBD oil has not yet been licensed in the UK as a medicine but can be prescribed by doctors in special circumstances.
The oil containing the THC chemical is illegal the under misuse of drugs legislation.
"I am a single mummy and he sleeps beside me and goes everywhere with me. I go to school with him.
"He is just my life," she added.
When Billy first got the treatment in the United States, Ms Caldwell said it helped the "brutal condition".
"I remember sitting up watching him at night in Los Angeles and touching him to make sure he was still breathing in case I had missed a seizure."
She said her "heart sunk" when she heard the news.
"I know if he hasn't access to this medicine his seizures will return," she said.