In a survey of 76 general practitioners published today in the New Zealand Medical Journal 42 said a patient had asked for a prescription for medicinal cannabis in the past year, but only 14 had written prescriptions.
Leading author Karen Oldfield, of the Medical Research Institute of New Zealand, said cost, special approval, and a lack of strong evidence put most doctors off.
"Those who have looked into prescribing it are coming up against some problems around access and the process, and those who aren't necessarily prescribing it have issues around the evidence base for it and the products that are available in New Zealand."
Other than Sativex - an oral spray that combines Tetrahydrocannabinol (THC) and cannabinoid (CBD) - there is no Medsafe-approved cannabinoid-based medicine in New Zealand. Sativex is approved for management of multiple sclerosis, but it not subsidised by drug-buying agency Pharmac.
GPs require hospital specialist as well as Ministry of Health approval to prescribe cannabis-related products, with the exception of medicinal cannabidiol or CBD or Sativex for multiple sclerosis.
Most - 84% - said they would be "somewhat likely" or "very likely" to prescribe a Pharmac-approved, funded cannabis product if it was backed by good evidence.
"I think the study says that GPs are open to prescribing medicinal cannabis product that has gone through all the testing that any other medication has gone through," Dr Oldfield said.
"If it's going to be treated as a medication it needs to be tested as a medication, trialled as a medication, then it would go into the pile of medications that can be trialled for people in specific medical conditions."
Only 43 doctors - 57% of those surveyed - were aware of Sativex, but most indicated they would be prepared to prescribe it for pain, multiple sclerosis and epilepsy or seizures.
Doctors generally accepted that there was strong evidence for treatment in multiple sclerosis, and some epilepsy syndromes, Dr Oldfield said.
"I think in all areas there needs to be a lot more robust evidence. I'm very supportive of studies and trials so the conversations can be had."
Dr Oldfield said the authors did most of the surveys face to face, so it relied on the doctor's on-the-spot general knowledge.
The survey suggested people were using cannabis for health reasons without a prescription anyway, and two-thirds of the doctors surveyed said patients had told them they had used cannabis unlawfully in the past year - usually smoking it to relieve pain, anxiety, or for cancer and palliative care.
Dr Oldfield said it was in line with the 2012/13 New Zealand Health Survey results, which found 42% of cannabis users said they had taken the drug for medical reasons.
As interest in the use of cannabis as a medicine grows, GPs were likely to be fielding questions from their patients about it and requests for its prescription for a wide range of conditions, Dr Oldfield said.
Having good quality, easy-to-access information was essential for GPs to be able to have informed conversations with their patients.
Dr Oldfield said she would like to build on her research by talking to healthcare professionals in other areas as well as patients.
In December, Health Minister David Clark announced new medicinal cannabis regulations would be introduced in April this year. These regulations will set out the quality and licensing requirements for manufacturing and distributing medicinal cannabis.
At the announcement, Dr Clark said 20 companies in New Zealand were already licensed to grow cannabis for research purposes and he expected some would apply for licences for medicinal cannabis.
Increased competition from local manufacturers should also drive down the price of costly medicinal cannabis products currently sourced from overseas, Dr Clark said.
