A former New York Times journalist has warned New Zealand against legalising recreational cannabis, saying its risks have been "substantially understated".
Alex Berenson is the author of a controversial new book Tell Your Children: The Truth About Marijuana, Mental Illness, Violence. He is in New Zealand as a guest of Family First.
Berenson spoke to Magic Talk's Peter Williams on Monday to explain why he believes recreational cannabis shouldn't be legalised.
"The harms of cannabis are quite a bit larger than are generally realised."
He believes there's no difference between recreational and medicinal cannabis.
"There's CBD - a chemical in cannabis that a lot of people use - it's non-psychoactive, it doesn't get you intoxicated [and] it doesn't seem to have the same risks as THC," he said.
"THC is the drug they use when they want to get high - that's what people who smoke cannabis want. They want to be high.
"People who take CBD don't want to be high - they're taking it for pain relief, or sleep, or arthritis.
"So there's THC v CBD, then there's medical v recreational cannabis. Medical and recreational cannabis are the same drug.
"When cocaine became popular in Europe in the 1880s and 1890s doctors thought it was medicine. They would give it to people for just about anything because people like excuses to take drugs that make them feel good and it has nothing to do with whether they treat any underlying disease, and it's exactly the same with cannabis."
Berenson said high-THC forms of cannabis can cause temporary forms of psychosis.
"I'd say there are some people who disagree, but most psychiatric researchers would agree that it substantially increases your risk of developing schizophrenia," Berenson told Magic Talk. "Especially if you start using [it] as a teenager and especially if you use [it] heavily."
Last year, however, academics from the University of Otago slammed Family First claims about links between psychosis and cannabis.
"They want to draw a straight line between cannabis and violence, and there's really no credible evidence of a straight link between the two," Associate Professor of psychological medicine Joseph Boden told The Spinoff, adding Family First's stance was "sloppy".
"As scientists, one of the things that we actually have to do apart from maintaining our objectivity about these things is actually to call out when people are misusing research."
Berenson said the situation was complicated.
"We, in the US, have almost no good statistics around psychosis and schizophrenia - we don't know what's happened to it in the last generation."
In December, Justice Minister Andrew Little revealed the proposed recreational cannabis scheme that will be put to New Zealanders at a referendum alongside the 2020 general election. A draft of the Cannabis Legalisation and Control Bill suggested a minimum purchase age of 20, a ban on marketing or advertising cannabis products and not allowing consumption in public areas.
"The public of New Zealand needs to know what they will be voting on and to have time to consider it properly.
"In particular, we welcome the focus on consumer safety. It's also heartening to see the commitment to running a public education campaign in the lead up to the referendum," Chris Fowlie, a spokesperson for cannabis reform organisation NORML, said at the time.