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Cannabis plants grow outside at The Republic cannabis farm and dispensary in Boulder on Friday, Sept. 16, 2022. (Andy Colwell, special to The Colorado Sun)

Colorado public health experts have unveiled a first-of-its-kind interactive research database containing hundreds of studies on the impacts of high-potency cannabis products — looking at the effects on everything from mental health to cancer to pregnancy.

That is one of the most significant things to come out of a two-year research review by the Colorado School of Public Health.

The review was ordered up by the legislature in 2021 in response to the increasing number of high-concentration THC products dominating the state’s legal cannabis market. With the rise of those products came concerns over how they may be impacting health, especially among young people. (THC is, of course, the most famous psychoactive chemical in cannabis.)

Researchers termed the report a “scoping review” and described the research database as an “evidence map.”

“With funding from the state of Colorado, a valuable, public resource has been developed for public health and scientific purposes,” Dr. Jonathan Samet, the school’s dean, said in a statement. “The scoping review and evidence map are unique; it is the first and most complete systematic assessment of the entire body of literature related to high-concentration cannabis.”

But what do those studies say? Eh, that’s a little less clear.

“Limited evidence” for most effects

The School of Public Health researchers found limited to no evidence in published studies for most commonly claimed effects.

Are adolescents and young adults especially vulnerable to adverse physical and mental health outcomes from using high-potency cannabis? There’s a limited amount of evidence that they are.

Do high-potency cannabis products help with pain? There’s a limited amount of evidence that they do.

What about sleep? There’s a limited amount of evidence that the products can both help and hurt sleep.

The review found moderate evidence — meaning slightly more robust but still not conclusive evidence — of only two impacts.

“There was a moderate amount of evidence that high-concentration THC can have adverse effects on those with pre-existing conditions such as psychosis,” Greg Tung, an associate professor of health systems, management and policy at the School of Public Health, said in a statement. “But there are also studies that show beneficial outcomes from the use of high-concentration cannabis on other mental health conditions such as PTSD, anxiety, and depression.”

Dr. Jonathan Samet, the dean of the Colorado School of Public Health, speaks during a July 9, 2020, news conference with Gov. Jared Polis at the governor’s mansion. (Jesse Paul, The Colorado Sun)

“It’s not an easy scientific question.”

In an interview, Samet said he wasn’t exactly surprised that the review didn’t come up with more conclusive answers.

One of the problems was the studies they had to work with. The research team at the Colorado School of Public Health screened roughly 66,000 studies and found 452 that were relevant to their questions about high-potency THC.

But what the team really wanted to examine was the effects of the kind of high-THC products sold today in the cannabis marketplace. The studies looking at the effects of THC spanned some five decades, meaning the products in those studies varied greatly and were often quite different from what is sold today.

Another problem: Studies funded by the National Institutes of Health were constrained to using cannabis from the government’s official research pot farm at the University of Mississippi. Cannabis from that facility is notoriously low quality.

“We learned there was a vast number of studies, potentially,” Samet said. “But that in fact there were not that many that directly addressed the policy questions we were interested in.”

It’s also not particularly easy to study effects when there are so many other elements that can go into the equation besides potency. For instance, Samet said the method of consumption could have an impact, as could the amount consumed and the tolerance of the consumer.

Samet, who is both a pulmonary physician and an epidemiologist, compared the task of studying potent marijuana to another research topic he knows well, tobacco smoking. Before the proliferation of tobacco vaping, studying smoking was pretty easy. There were only a handful of different consumption methods and a cigarette generally provided a tidy, standardized dose.

By contrast, trying to study cannabis today introduces a dizzying number of variables.

“It’s not an easy scientific question,” Samet said. “It’s not easy to generate the data you would like.”

Getting to the underlying answer

To Samet, getting better answers to questions about the health impacts of high-potency THC will require more uniform studies.

In other words, researchers across the country and the globe need to come up with consistent standards to use and consistent ways of measuring data. Having those standards in place would allow studies to be better compared and synthesized.

But, in the meantime, he says the Colorado School of Public Health review should come with a caution. While it may be tempting to look at the limited evidence on effects and conclude it means high-potency THC isn’t harmful, Samet said it’s better for consumers to err on the safe side. After all, as the old scientific saying goes, absence of evidence is not absence of harm.

“We’ve certainly highlighted the complexities,” Samet said. “I wish we had found more definitive evidence.”

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John Ingold

John Ingold is a co-founder of The Colorado Sun and a reporter currently specializing in health care coverage. Born and raised in Colorado Springs, John spent 18 years working at The Denver Post. Prior to that, he held internships at the Rocky Ford Daily Gazette, the Colorado Springs...