Alex Renton, who is in an induced coma following an undiagnosed seizure.

A teenager in an induced coma in Wellington Hospital is the first to have received a cannabidiol product signed off by a Government minister.

On Tuesday Associate Health Minister Peter Dunne approved the one-off use of Elixinol, a cannabidiol (CBD) product from the United States for Alex Renton.

The 19-year-old Nelson man has been in hospital since early April and remains in "status epilepticus", a kind of prolonged seizure.

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Dunne said doctors have been able to apply for medicinal cannabis products for many years but this is the first time this particular avenue has been used for this particular product.

"I received the advice from the Ministry of Health this morning and that advice was 50/50 saying that there's no compelling evidence that this product will work. On the other hand there's no compelling evidence it will do significant damage to him."

But Dunne stressed this wasn't a precedent and shouldn't be seen as a "significant change in policy".

Alex's family have been fighting for weeks to try an alternative treatment after more than 20 conventional medications failed to help the teenager.

Alex's mother, Rose Renton, said she was incredibly relieved for her son.

"I'm over the moon the hospital supported their promise and Peter Dunne is compassionate. New Zealand is relieved too, I think."

Dunne said the family had been issued with import permits to source the CBD as soon as possible.

"I'm told it's not difficult and can be done within a few days," he said.

On Monday Renton and supporters held a protest outside the hospital, and on Tuesday a small group of protesters were outside the Ministry of Health calling for greater access to medicinal cannabis.

Dunne said the protests played no part in influencing his decision and did more harm than good.

"They're not helpful in these situations."

The Capital and Coast District Health Board made an application to the Ministry of Health on behalf of Alex on Monday.

Dunne said ministry officials considered the application "as a matter of priority" and after he was briefed on Tuesday morning he made the decision to approve it.

"Despite the absence of clinical evidence supporting the efficacy of CBD in patients with Mr Renton's condition, status epilepticus, my decision relies on the dire circumstances and extreme severity of Mr Renton's individual case".

"I have also considered the absence of any other treatment options, the low risk of significant adverse effects, and the conclusion reached by the hospital ethics committee from an individual patient perspective," he said.

On Monday Prime Minister John Key said he wouldn't support a debate in Parliament for broader access to medicinal cannabis because there were other alternatives.

Key said that, while his advice on the subject could change, he was not "actively looking to progress" a parliamentary debate on the topic.

Dunne contacted Key to inform him of his decision to approve the treatment and said the Prime Minister was "very supportive".

"We didn't talk more widely about the issue. I told him particularly about this individual case..."

Labour MP Damien O'Connor said on Monday that the country was ready for a debate on the subject, and if that meant submitting a member's bill or calling for a select committee inquiry, then he would be the driver of it.

Following Dunne's decision, O'Connor said he hoped the treatment would help Alex and he would continue to progress access to CBD for others.

Dunne said Alex's application had been considered as a "stand-alone case and weighed against the severity of his condition".

"My officials will be closely following the outcome of studies overseas, including those due to commence next year in Australia, on the efficacy of different products. Those results will help to inform future legislative and regulatory considerations here in New Zealand."

"I hope for a positive outcome for Mr Renton and his family," he said.