The wheels are in motion to allow doctors to prescribe cannabis-based products as a medicine, but it is unclear how long it will be before they can do so regularly.

On top of procedural steps needed to change the rules, a more difficult issue is the lack of availability of products that meet New Zealand requirements.

Associate Health Minister Peter Dunne announced on Friday that restrictions will be removed around cannabidiol (CBD) - a substance with therapeutic value found in cannabis but with "little or no" psychoactive properties.

Up until now CBD has been classed as a controlled drug under the Misuse of Drugs Act. Cabinet has decided it should cease to be a controlled drug. That means doctors will be able to prescribe CBD to their patients, and it can be supplied the same way as other prescription medicines.

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When will it cease to be a controlled drug under the Misuse of Drugs Act?

There is no timetable but Dunne's office is saying "as soon as possible" and "in the very near future". Dunne's spokesman said a regulatory change was needed, not a legislative one, so it could be done "relatively quickly".

What are some of the other hurdles?

For a doctor to be able to prescribe CBD it will have to have 2 per cent or less of other cannabinoids. Dunne said there was a "limited" range of CBD products available that were made to a suitable quality.

Clinicians would be likely to only prescribe products made to quality manufacturing standards, Dunne said.

Could patients just import their own CBD product?

In that case the patient's clinician would still need to get Ministry of Health approval to prescribe the product, and an import licence would be needed.

So what's the point?

According to Dunne, the change will "streamline the process" for access to suitable products when they become available. He talked about one product called Epidiolex, which is in clinical trials.

"It takes time for products to go through the research and development process which includes clinical trials to establish evidence for the effectiveness of a product and for its safety for particular patient groups," Dunne said.

"The proposed changes will mean that as more CBD products are made to a suitable quality become available, they will not be subject to unjustified storage and prescribing restrictions."

Prescriptions for three months' supply will be allowed, rather than the one month that has been the rule.

What is CBD good for?

In 2015, Dunne approved the use of US-made CBD product Elixinol for Alex Renton, 19. His mother Rose Renton had campaigned to be able to use medicinal cannabis in her son's treatment in the hope it would reduce mysterious seizures he was suffering, and bring him out of a coma.

In December 2016, Auckland woman Dr Huhana Hickey received approval to use cannabis extract Tilray to help with treatment for multiple sclerosis.

Also last year, Dunne approved a non-pharmaceutical grade cannabis-based product called Aceso Calm Spray for a patient with a severe case of Tourette's Syndrome.

In a 2016 submission, the Ministry of Health said Epidiolex - a pharmaceutical grade CBD product - was undergoing clinical trials in the US in the hope it could be used to treat rare forms of epilepsy, such as Dravet syndrome.

"Research indicates that CBD could have several therapeutic applications. Some of the effects that have been reported to date include anti-seizure, neuroprotective, anti-inflammatory, analgesic, anti-psychotic and anti-anxiety effects," the ministry said. But at the time it said more clinical trials were needed to confirm its effectiveness.

A paper prepared by Dr Keith Bedford last year for the Expert Advisory Committee on Drugs said there was limited evidence suggesting cannabis could be used to reduce medical treatment side effects, such as nausea and vomiting during chemotherapy, improved appetite in people with HIV/AIDS, and in the treatment of chronic pain and muscle spasms.

A product called Sativex - a spray derived from strains of cannabis containing a mixture of THC and CBD - had been approved by Medsafe in this country as an add-on treatment for improvement of symptoms in patents with moderate to severe spasticity due to MS who had not responded adequately to other anti-spasticity medication.

How about manufacturing CBD products in New Zealand?

Not in a hurry, it would seem. According to Dunne, the law only allows domestic cultivation and manufacture of cannabis-based products for clinical trials.

So it will be up to doctors to decide who can have CBD products and what for?

Yes, and Dunne said they needed to make informed decisions, just like they did for all medicines. "If a doctor does not think there is adequate clinical evidence, that the potential risks outweigh the potential benefits, or that there simply is not enough information to be assured of the composition and quality of a particular product, they should not prescribe it."

Will the Government fund CBD products?

Anyone can make an application to Pharmac to fund a cannabis-based product or products, Dunne said.