Mr Dunne said the need for "fine-tuning" was inevitable, given that medical cannabis was a new policy area for the Ministry of Health and wider medical profession.
"The guidelines were set up at my request following the Alex Renton case in 2015, so far the only case where ministerial approval was granted, following an application from Mr Renton's treating clinicians to administer the restricted product Elixinol."
Mr Dunne said the guidelines were more recently applied to an application for medical cannabis made on behalf of former Council of Trade Unions head Helen Kelly, but subsequently withdrawn by her oncologist before any ministerial decision was required.
"While I am satisfied that on the whole the guidelines are sound, they were prepared as guidance only. They allow for flexibility across different clinical situations, and are certainly not set in stone as some have claimed.
"Nonetheless, some further review would be beneficial and I have asked officials to undertake further consideration of them. I am not ruling out seeking external input into this review process."
Mr Dunne said he would be discussing these issues in Canberra next week at the Australian Drug Foundation's National Drug Summit.
In Australia, the federal Parliament passed legislation on Wednesday to legalise the cultivation of cannabis for medicinal purposes. The government is now expected to take at least six months to write the regulations to allow cannabis to be grown legally under licence.
In January, Ms Kelly wrote to Mr Dunne to seek permission to use medicinal cannabis.
Ms Kelly, who has terminal lung cancer, was already using cannabis oil to ease her pain, and said the drug had been "brilliant" for helping with nausea, lost appetite, and pain relief following chemotherapy.
She now wants a legal, regular supply of the drug. Patients can apply to the Ministry of Health to get access to one form of medical cannabis, Sativex, which has been cleared for use in New Zealand.
Ms Kelly sought approval for a non-pharmaceutical-grade cannabis which does not have approval in New Zealand.
Earlier this month, the ministry responded to her application, saying it would be deferred because it did not contain enough information.
"Basically they've said my doctor hasn't described enough how the current drugs I'm taking are not working," she told Radio New Zealand at the time.
"He's described all the drugs I'm taking and he's a senior oncologist and he said, 'I'm seeking permission to give her cannabis', but ... they're second-guessing him."
