Doctors aren't prescribing much medicinal cannabis, despite a growing number of patients asking for it.
Researchers surveyed dozens of doctors, and found in the past year 55 percent had been asked for it by patients, and two-thirds of patients were already using it illegally - mostly just smoking it.
But only a third of those doctors whose patients requested medicinal cannabis actually tried to prescribe it - 14 out of 42 - and of those, only eight ended up receiving their prescription.
Thirteen of the 14 doctors reported difficulty prescribing the medication because of the "confusing regulatory process", according to the study, published in the New Zealand Medical Journal on Friday.
Apart from cannabidiol (CBD) products, at present, ministerial approval is required to prescribe most cannabis-based medicines. Then-Associate Health Minister Peter Dunne delegated this authority to the Ministry of Health a few years ago. The only exception is Sativex, but only if the patient has multiple sclerosis.
Doctors are presently allowed to prescribe CBD products without ministry approval, as cannabidiol doesn't have any psychoactive properties. But they're currently unapproved - meaning they haven't been through the usual regulatory process, and there are greater obligations on the prescriber, including getting informed consent from the patient and notifying health authorities.
Doctors who didn't prescribe said the high cost of the unsubsidised medicines was putting them and patients off, while others either weren't aware of what cannabis-based medicines were available, or don't think there's good enough evidence that they work.
Despite the medicinal cannabis scheme set to become law at the start of April, many doctors appear not to be ready. More than 40 percent in the survey admitted not reading anything about how cannabis products could be used as medicine, and only slightly more than half could name a single cannabis-based medicine brand - mostly Sativex - but few could say what was in it.
They were more likely to know about its negative effects, the researchers said.
"The majority of GPs were informed as to the potential side effects of using cannabis-based medications, likely reflecting knowledge of the adverse effects of recreational/illicit cannabis use.
"A minority were aware of the annual cost to patients (approximately $14,500) for the PHARMAC-approved indication for prescribing. This is not unsurprising, as the prevalence of multiple sclerosis in New Zealand was most recently recorded as 73.1/100,000, meaning many GPs may not have experience with patients who have multiple sclerosis and do not have experience prescribing Sativex."
A majority of doctors expressed reservations about prescribing unapproved cannabis-derived products in the future without stronger evidence they work.
"With the upcoming implementation of the medical cannabis scheme it is important that educational programmes emphasising evidence (both for and against use), medico-legal and practical elements of prescribing are in place to support the GPs to have informed discussions with their patients," the New Zealand Medical Association said in a statement.
There are currently no CBD-based medicines funded by Pharmac, nor is Sativex.