Massey researchers are questioning a report which they say overlooks the risks that will come with legalising cannabis.
The Sense report projects up to $249 million could be collected in tax and licensing fees from legal cannabis sales.
But, in a New Zealand Medical Journal article, Massey University researchers say this must be balanced against the additional health and social costs from increased cannabis use.
Co-author and Massey University Associate Professor, Chris Wilkins told Mike Hosking the report assumes there will be no additional harm from cannabis under legalisation.
"The point of cross benefit analysis is to not only show the most optimistic possible outcome but give you a sense of the level of risk."
He said they looked to experiences in Colorado, the US state which has had commercial, recreational and medicinal cannabis the longest.
The research has found there have been increased hospitalisation, emergency department submissions and calls to poison services.
New Zealanders will vote in a referendum on personal use of cannabis at next year's general election.