The mother of a severely epileptic boy who was the UK's first patient to receive marijuana legally on the NHS is to lobby MPs this week after the Government halted his prescription.
Billy Caldwell, 11, from Castlederg in Co Tyrone, has a form of the condition meaning he cannot get help through medication or diet.
He used to suffer up to 100 seizures a day until he began treatment with cannabis oil in the US, where medical marijuana is legal, in 2016.
In Northern Ireland, he became the first person in the UK to receive a prescription after his local GP Brendan O'Hare began writing scripts.
The doctor was summoned to a meeting with Home Office officials recently and told to desist.
Billy's mother, Charlotte, is meeting MPs and speaking at a conference on medicinal cannabis use in London this week.
A family spokesman said: "The Home Office are determined not to open the flood gates on this."
In England, Alfie Dingley's family have been engaged in a similar battle through the courts.
Billy's family statement said the Home Office were trying to create a bespoke solution for Alfie without setting a precedent.
He added: "The Home Office have been trying to get off the hook for months with Dingley by coming up with a solution for him."
He said medicinal cannabis use was being adopted around the world, but not in the UK.
"There are many forms of epilepsy and particular ones are immune to treatment apart from cannabis.
"She (Mrs Caldwell) cannot contain her son's seizures without access to it."
Charlotte Caldwell has said Billy has been free of the debilitating episodes for a considerable period since the treatment.
SDLP Foyle Stormont Assembly member Mark H Durkan said: "I am appalled that the Home Office have reacted so heavy-handedly to a very sensitive and high profile case.
"It has been clear from the start that Billy's GP has issued this treatment in good faith to save a young boy's life, not to open the floodgates to inappropriate drug use.
"Medical professionals sign a Hippocratic oath to ensure patients get the care they need, and this action by bureaucrats has undermined that oath."
He said the SDLP will be writing to the Home Office to ask them to retract the letter sent to Dr O'Hare on the basis that a child could needlessly die.
"This is another example of why we need the Assembly reinstated as a matter of urgency to ensure we can make our own laws around these sensitive issues and not take direction from London."