Eminent horticulture researcher Dr Mike Nichols in a cannabis plant factory in the Netherlands. He is one of only 25 honorary members of the International Society for Horticulture Science.

New Zealand should grow medicinal cannabis because of its potentially good returns, a Massey University scientist says.

Dr Mike Nichols, who has also researched hemp growing, said New Zealand risked losing out on a profitable industry, in the same way it once turned down the chance to grow poppies for legal codeine and morphine.

Even though New Zealand scientist Ralph Ballinger was the world's lead researcher into poppy growing in the 1950s, his work never resulted in an industry.

CAMERON BURNELL/FAIRFAX NZ Union advocate Helen Kelly recently highlighted the issue of medicinal cannabis as a painkiller.

Instead, Tasmania now supplies 40 per cent of the world's legal codeine and morphine, earning more than $200 million a year for the state.

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Just why the decision was made to discontinue the work is uncertain. Nichols blames "political" forces.

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"The frustrating bit is he [Ballinger] was in the same rest home as my brother and sister-in-law in Blenheim and when I used to go over to see him I never asked him the hard questions," Nichols says.

Ballinger died last year at the age of 99.

Nichols says he does not see a lot of economic value in hemp growing, but he believes New Zealand's horticulture innovation and technology would give it a competitive advantage when it comes to medicinal cannabis.

And gram for gram, cannabis would outdo most exports.

"It costs a lot of money to send a log to China and you don't get much for it. But you could send 1 kilogram of medicinal cannabis and you'd get thousands of dollars for it," he says.

China would be a likely market because the Chinese are keen on using natural plant products for medicine.

That said, no-one in New Zealand has carried out a cost: benefit analysis of the crop.

In the meantime Australia and other countries are already stealing a march on New Zealand with their work.

Wealthy Australian couple Joy and Barry Lambert recently donated $36.3 million to fund medicinal cannabis research at Sydney University.

Nichols said there were two methods of growing it: either in a totally controlled plant factory or a greenhouse.

"Factories seem to be the way things are going because you don't want to use pesticides on it [cannabis], therefore you have to keep bugs out, and you're more likely to do that in an enclosed system where air is filtered in."

He is soon to visit Ontario, Canada, where producer Aphria is growing medicinal cannabis in a greenhouse.

Nichols said Aphria's 12 varieties sell for about $9 a gram, or half the price of illegal cannabis in New Zealand.

As with poppy growing, no research can be carried out in New Zealand on cannabis without government approval.

Under current legislation this approval is wanting.

"If someone wishes to cultivate cannabis for consumption, injection or smoking for other than research and study purposes, for example commercial production of a medicine, this could not be licensed under the current legislation," says Michael Haynes, manager medicines control with the Ministry of Health.

Any changes in legislation would need to take into account the requirement of the Single Convention on Narcotic Drugs 1961 which requires signatory countries, such as New Zealand, to establish an agency that purchases and takes physical possession of the crop as soon as possible, but not more than four months after the end of the harvest.

Plenty of "home research" has been carried out over the years but none of it has been peer-reviewed, Nichols says.

Only UK company G W Pharmaceuticals has conducted "acceptable" medical trials with medicinal cannabis, he maintains.

There are a lot of unanswered questions over how to best grow it.

Nichols speculates a hydroponic "ebb and flow" system might give a better yield than growing in soil.

But he is unsure over the nutrient mix, optimum plant density and lighting (its intensity and wavelength), and whether to use a greenhouse or plant factory.

On a visit to a plant factory in Holland several years ago, he saw high pressure sodium lights being used. Now long life and more efficient LED lights would be used.

From his days researching hemp, Nichols knows they are not very nutrient-hungry plants, but he notes there would be a big difference in returns if yields were increased with the addition of fertiliser.

Cannabis has several important attributes: while there are male and female plants, the drug content is found largely in the unpollinated female flower heads.

This means plants should be grown from cuttings from "mother plants"; these cuttings are then encouraged to produce flowers by artificially giving them short days, using blackout curtains.

In a plant factory under artificial lights, as many crops a year as wanted could be produced.

Nichols, who was a team leader for the New Zealand Hemp Industries Association from 2001, says hemp was not economic for the three purposes it was grown: to take nutrients out of the soil, as an oil seed, and for fibre.

"The problem is hemp is an annual crop, so as a 'mop crop' it's more expensive than a perennial like willow which you harvest but regrow.

"For oil seed and fibre, you have to get the ground prepared every year, seed is attractive to birds, and possums like hemp," Nichols said.

His views are not shared by hemp enthusiasts who say the same could be argued about any annual crop.

Regarding the view that medicinal cannabis will open the door to recreational cannabis, Nichols says the same could be said about any drugs. Some people become addicted to painkillers which are freely available.

Besides ameliorating childhood epilepsy and being an effective painkiller for other ailments, cannabis is a far safer drug than alcohol, he says.

"In New Zealand the producers and purveyors of alcohol may receive knighthoods, while the equivalent cannabis suppliers may receive a prison sentence."