A review which left the rules for access to medical cannabis largely unchanged was 'biased', an open letter from advocates says.
Associate Health Minister Peter Dunne had Ministry officials and medical professionals look at guidelines used to assess applications for prescribing cannabis-based products.
The review concluded there was a lack of data to support using the products.
Now a group of medicinal cannabis advocates, including the trade union leader Helen Kelly, have signed an open letter denouncing the review, saying it has biased methodology, and misleading and deceptive scientific claims.
They have called for an independent inquiry into medical cannabis products.
Southland Hospital consultant anesthetist Paul Wieland told _Nine to Noon_the rules for prescribing the drug were very strict, and costly.
"It's so ridiculously expensive, it costs ... twelve or thirteen hundred dollars a month, and who can afford it."
He said there was not enough good data on medical cannabis worldwide because of the legal status of the drug.
"For example in ... the United States it is nigh impossible to do cannabis studies unless you look at negative side effects because they have to be approved by a number of political bodies.
"For some reason many politicians seem still to be locked into this Reefer Madness thinking that was so prevalent in the 30s and 40s," Dr Wieland said.
A lot of the evidence for the positive effects of cannabis was based on anecdotal accounts, or came from case studies, he said.
"What is really needed to happen is for some clinical trials involving the whole cannabis plant."
Nelson chronic pain sufferer Rebecca Reider, who was recently discharged without conviction for importing a cannabis pain relief product, said Mr Dunne is "categorically resistant" to the drug, and there is a strong anti-cannabis bias in the review.
She said the doctors who provided the advice for the review did not have specific medical cannabis training, and the legal status of the drug made it hard for doctors to get familiar with it.
There are growing number of studies that showed the efficacy of cannabis, but people were forced to self-medicate could be dangerous, Ms Reider said.
Associate Health Minister Peter Dunne declined to appear on Nine to Noon.