The Associate Health Minister is allowing a Nelson teenager a one-off use of cannabis oil.

LISTEN: Peter Dunne - Cannabis oil for coma teen

19-year-old Alex Renton has been in an induced coma in Wellington Hospital for two months, after suffering a seizure.

More than 20 medications haven't worked, so the family desperately want to try a form of cannabis oil.

Associate Health Minister Peter Dunne told Newstalk ZB he made the decision based on advice from doctors, and he wanted "to make it clear that this is not a precedent for other cases".

The product needs to be imported from the US.