Charlotte Caldwell was attempting to bring the drug into the UK for her severely epileptic child when she had it confiscated by customs officers in London after a flight from Canada.
She was not cautioned, and has vowed to repeat the attempt.
“We will not stop, we are not going to give up,” she said after the medicine was seized. “We have love, hope, faith for our kids and we are going to continue.”
Her son Billy, 12, was given a prescription for medicinal cannabis oil last year to help treat his epilepsy – the first time the drug had been prescribed by the NHS.
But the boy’s doctor was told by Home Office drug enforcement teams to stop prescribing the medication, which Ms Caldwell credits with keeping her son’s seizures at bay.
Billy, from County Tyrone in Northern Ireland, suffers serious fits and Ms Caldwell is worried the cycle of seizures “will eventually kill him”.
She described the drug as “a small bottle of oil that’s keeping my son alive”.
After arriving at Heathrow on Monday she met Home Office Minister Nick Hurd. She said she asked the MP for the medicines to be returned, but was refused.
She then asked for a solution and was assured the Home Office would return with a response at 5pm.
She said she had an “honest, genuine” conversation with Mr Hurd in the “parent to parent” meeting following a 20-hour trip between Toronto and London with her son.
She told reporters that customs officers at Heathrow were “absolute gentlemen… really, really nice,” and one even had tears in his eyes as they took the drug from her.
Earlier this year, Ms Caldwell said: “Medicinal cannabis has given me back my right to hope and try to live some kind of normal life. But most importantly it has given Billy the right to life.”
“My child will not go without life-saving medication. How I get it remains to be seen. But I will.”