Alex Berenson, former New York Times investigative reporter turned author, says he wants to sound the alarm about research into marijuana and mental illness at a time when many states are legalizing or thinking about legalizing cannabis for medical and recreational use.

In his new book, “Tell Your Children,” Berenson argues the case, citing research from the National Academy of Medicine. On page 289 of the NAM’s 2017 report, “The Health Effects of Cannabis and Cannabinoids,” the nonprofit group concluded there is a risk. “Cannabis use is likely to increase the risk of developing schizophrenia and other psychoses; the higher the use, the greater the risk,” wrote the NAM, which advises the U.S. government on health issues.

Berenson told CNBC on Tuesday the NAM “did a 500-page report that says basically that nearly all the medical benefits are either unproven or don’t exist, and there’s a true link to psychosis and schizophrenia, which are terrible diseases.”

Morgan Fox, a spokesman for the National Cannabis Industry Association, downplayed Berenson’s research in a statement emailed to CNBC.

“The connection between cannabis consumption and mental illness is tenuous at best, and the fact that we don’t know more about it is just another reason to change policy so that it can be more easily researched,” he said.

“So far, there is nothing to suggest that cannabis consumption causes mental illness, though some research suggests that it may exacerbate pre-existing conditions,” Fox said. “There are tens of millions of regular cannabis consumers in the United States, and if it was truly a contributing factor to mental illness, we would be seeing widespread negative effects, and we simply are not seeing that.”

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