There's not enough evidence that e-cigarettes are an effective tool in helping people quit smoking, the Ministry of Health says in a cabinet paper presented to government ministers.

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Public consultation on legalising e-cigarette sales began in August and closed earlier this week.

E-cigarettes are electrical devices that mimic smoked tobacco by heating a liquid which produces a vapour that the user inhales.

The sale of e-cigarettes is currently illegal if they are used to vape nicotine derived from tobacco or if they were sold on the basis that vaping would help someone quit smoking.

The cabinet paper, from July, has been released by Associate Health Minister Sam Lotu-liga said that while the Ministry of Health believed vaping was less harmful than smoking, it advised against the legalisation of e-cigarettes on the justification it could be used as a smoking cessation tool.

"There is not yet enough evidence to be able to recommend e-cigarettes as an aid to stop smoking," the paper said.

People seeking to quit were advised to contact the Quitline or use approved medicines such as nicotine patches, it said.

Only approved medicines can be sold for smoking cessation and so far only one e-cigarette company was in the process of doing so.

That company had been granted marketing authority for smoking cessation in the United Kingdom. A manufacturer wishing to make a similar claim in New Zealand must apply to Medsafe for approval to supply their product as a medicine.

That process cost between $7000 and $88,000.

While there is some evidence to suggest vaping was less harmful than smoking tobacco, there was not yet enough data on the short-term or long-term impact of e-cigarette use on a user's health, or even on their ability to quit nicotine altogether, the paper noted.

"There is concern young people's experimentation with, and the use of e-cigarettes, may lead to nicotine addiction and/or have a gateway effect leading to young people taking up smoking," it said.

There was also evidence of an increase in New Zealand of young people trying e-cigarettes and a concern that the industry was targeting them with appealing flavours like chocolate or strawberry.

"There are indications that tobacco industry involvement has been increasing over the last few years, however, we do not have information available to quantify their current market share," the paper said.

E-cigarettes should be available - professor

However, an associate professor of public health at Massey University, Marewa Glover, said there was no evidence that e-cigarettes encourage young people to take up smoking.

"Flavours are very very important for the adults, and for the people who are switching over from smoking.

"It is very very important we don't mess with that, and we don't put unnecessary and unfounded restrictions in the way of adults switching to vaping."

The devices should be freely available to help people quit tobacco, she said.