The mother of a girl with epilepsy said her child is at risk of "becoming comatose" after her medical cannabis oils were seized at a UK airport.
Tannine Montgomery said Indie-Rose, 5, had seizures and panic attacks before starting to use the oils 14 months ago.
Ms Montgomery, 30, said she was stopped at Stansted on Friday returning from the Netherlands, where she buys the oil with a prescription from her UK doctor.
She urged Health Secretary Matt Hancock to "sort this crisis out".
Campaigners claim just two NHS prescriptions for medical cannabis, which contains the psychoactive ingredient THC, have been issued since the government announced last year that doctors can prescribe such products.
'High risk of death'
Although Ms Montgomery, from Clare, Suffolk, has a private UK prescription to treat Indie-Rose's Dravet syndrome, she says it is cheaper to travel abroad to stock up on the oils.
"To obtain a special import licence would cost us £4,500 per month as opposed to the £1,500 we pay for the drug at the moment," she said.
"Seizing this medicine is condemning my lovely daughter to becoming comatose, wracked by seizures and to be at high risk of an unnecessary death.
"For the love of God, this medicine is legal in the UK and I have a full lawful UK prescription for it."
Although it is illegal to import cannabis oils without a special licence, Ms Mongtomery said UK Border Force officials have in the past let her into the country with the drug.
Ms Montgomery said of Mr Hancock: "We know he has the report on his desk from the NHS setting out why the system for NHS prescriptions is blocked.
"Every day he doesn't act on it is a day of interminable suffering for mothers like me.
"For families like us it's too much to bear the frustration of knowing that there's something that can transform the lives of our children but we are blocked from getting it."
Since the law was changed in 2018, parents have found they cannot easily access the medicines without paying thousands of pounds for an import licence.
In addition, many doctors cite a lack of official guidance as a reason for refusing prescriptions.
Peter Carroll, from the campaign group End Our Pain, added: "This is truly shocking. The law was changed last November so that patients who could benefit from medical cannabis could be prescribed it here.
"Indie-Rose's parents have a lawful UK prescription for this medicine. The recent report from the Health and Social Care Select Committee specifically said that the harassing of families at the border should stop."