The Home Office has rejected a County Tyrone mother's plea to legalise cannabis oil for her epileptic son.
Charlotte Caldwell accused Home Office minister Nick Hurd of having "likely signed my son's death warrant".
Ms Caldwell brought cannabis oil from Canada for her son Billy, but it was confiscated at Heathrow on Monday.
In 2017, the 12-year-old became the first person in the UK to be prescribed cannabis oil, but last month his GP was told he could no longer do so.
Ms Caldwell, from Castlederg, said she was "absolutely devastated" to have the supply confiscated after she declared it to border officials.
Ms Caldwell later met Mr Hurd at the Home Office to plead with him "parent to parent" to get the oil back.
"It's Billy's anti-epileptic medication that Nick Hurd has taken away, it's not some sort of joint full of recreational cannabis," she said.
"We had an honest and genuine conversation. I have asked him to give Billy back his medicines, but he said no."
She also warned of the dangers of Billy missing his first dose of cannabis oil in 19 months.
"The reason they don't do it is that it can cause really bad side-effects - they wean them down slowly," she said.
"So what Nick Hurd has just done is most likely signed my son's death warrant."
'Back to Canada'
A Home Office spokeswoman said it was "sympathetic to the rare situation that Billy and his family are faced with".
"The policing minister met Ms Caldwell and advised her that despite these extremely difficult circumstances, it is unlawful to possess Schedule 1 drugs such as those seized at the border this morning without a licence," she added.
"The minister urged the family to explore licensing options with the Department of Health Northern Ireland."
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.
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 under the misuse of drugs legislation.
Read more: The science of high-potency cannabis
Ms Caldwell says Billy's seizures have dramatically reduced while taking the cannabis oil, and she has vowed to keep fighting.
"I take the view that I'd rather have my son illegally alive than legally dead," she said.
"I will just go back to Canada and get more and I will bring it back again because my son has a right to have his anti-epileptic medication in his country, in his own home."
Billy was first given the treatment in the United States, where medical marijuana is legal.
He became the first person in the UK to receive a prescription after his local GP, Brendan O'Hare, began writing them.
The doctor was summoned to a meeting with Home Office officials recently and told to stop.