Chris Fowlie, co-owner of The Hemp Store in Auckland, discusses the merits around legalising cannabis.

New Zealanders need to have an informed debate about cannabis, distinguishing recreational use from the drug's potential medical application, psychiatrists say.

In the latest issue of the New Zealand Medical Journal, which includes studies on self-reported medicinal use of cannabis and the effect of law changes on synthetic cannabinoid use, an editorial argues for clear public debate.

Part of the problem in discussing cannabis use in New Zealand stems from difficulties obtaining reliable data about an illegal drug and the confusion around use of the term "medical cannabis."

Droplets of oil form on the surface of a cannabis plant in a state-owned agricultural farm in Rovigo, about 60 km from Venice, Italy.

University of Otago psychiatrist Dr Giles Newton-Howes and Capital and Coast District Health Board addiction psychiatrist Sam McBride, in a journal editorial, say objective research is difficult in New Zealand.

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Medical cannabis extract. One product, Sativex, is currently approved for medical use in New Zealand.

Investigating the potential uses of cannabis as a medicine was a sensible approach, although existing evidence was far from conclusive, the authors said.

A parallel approach was needed, focusing on the debate around decriminalising alongside continued investigation of the usage and regulation of medical cannabinoids.

One product has been brought to market in New Zealand, Sativex, a spray for the management of complaints associated with multiple sclerosis.

Unknown A public debate is needed about cannabis in New Zealand, which has a high rate of recreational use and self-reported ''medical'' use, according to a psychiatric report.

Broadly, there is clear evidence cannabis increases rates of psychosis and other psychological disorders while the available evidence around medical benefits is, so far, "weak" or "moderate."

Newton-Howes said a social debate was needed and it was important to stress the medical potential of cannabis separate to the recreational use, and abuse, of the drug. Terminology was not well defined, in stark contrast to the objective criteria used to define, for example, cocaine and medical application.

But, before the medical establishment reached the point where prescribing cannabis was possible, a public and social policy debate needed to happen.

"There's this massive crossover between patients who are using cannabis for what they perceive as medicinal as well as what they say is for pleasure.

"Medical cannabis - what that means and how it's used, or prescribed, is not very well defined," he said.

Evidence suggests medical use of cannabis can help some treatment of chronic pain and spasticity - spasms and stiffness.

An in-depth study by the Journal of the American Medical Association concluded there was reasonable evidence supporting the use of cannabinoids for pain and spasticity but low-quality evidence for management of, for example, nausea due to chemotherapy, sleep disorders and Tourette syndrome.

Another review of medical application found cannabinoids "showed promise" for some complaints associated with multiple sclerosis and limited evidence of benefits for patients with, for example, Parkinson's disease, Huntington's disease and epilepsy.

Other reviews and studies of cannabis and epilepsy have been inconclusive.

However, there is evidence of increased rates of psychosis among cannabis users, based on population studies, some of which were based on New Zealand subjects.

Newton-Howes, in the editorial, said caution was needed when discussing the potential use of cannabis as a medicine because of a lack of high quality New Zealand data about potential benefits.

As it stands, it was too early to promote medical access in New Zealand but a change in policy and a review of the legislative approach were recommended.

"[It] is clear the current prohibitionist approach does little to prevent cannabis use in New Zealand, although the regulatory measures related to synthetic cannabis suggest a harm reduction approaches have some impact.

"This is not to say that cannabinoids may not be valuable for some patients for some symptoms, nor that many of these problems cannot be overcome.

"Notwithstanding this, chasing a medicalised access route to cannabis use seems premature in New Zealand.

"While further work is undertaken to consider the most appropriate mechanism to use cannabinoids medically, a social discussion around the decriminalisation of cannabis can occur, without the distraction of "medical cannabis".

"This pathway forward recognises the high use of cannabis in New Zealand, the social harms of a prohibitionist legislative approach, the needs for further regulatory development and medical evidence prior to cannabis becoming a prescription drug.

"This is a public debate the medical profession needs to be actively engaged in, bearing in mind the role of medicine in the public arena."

In 2011, the Law Commission recommended legalising medical cannabis and softening the legal stance on recreational use, but legalisation is not on the Government agenda.

Ministry of Health guidelines say three types of cannabis products may be considered for medicinal use subject to ministerial approval; pharmaceutical grade products such as Sativex, other pharmaceutical grade products and non-pharmaceutical grade products that may be intended for use as medicine.

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