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CU Professors to Study Behavioral Impact of Cannabis Legalization

Two University of Colorado Boulder professors received $5.5 million to research how the legalization of cannabis for recreational use impacts human behavior.

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The University of Colorado Boulder announced last week that the National Institute on Drug Abuse (NIDA) has awarded two CU professors $5.5 million to study possible behavioral changes in the years since recreational use of cannabis was legalized in Colorado. According to CU, the study is the first and only of its kind in the nation. 

Behavioral geneticist John Hewitt and psychiatry professor Christian Hopfer, MD, will examine self-reported cannabis use as well as behavior and mood changes in more than 1,000 sets of twins each in Colorado and Minnesota ages 23 to 29. While Colorado adults have had legal access to recreational cannabis for more than three years, Minnesota prohibits recreational use of the drug. (As such, the out-of-state participants will serve as the study’s control group.)

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“We’d like to know about how the change in the legalization [in Colorado] is changing people’s behavior,” Hewitt says. He hopes to determine whether subjects have increased their cannabis use and whether they’ve turned to other substances (like alcohol) more or less frequently since legalization. He’ll also monitor changes in cannabis users’ moods, employment status, family functioning, and educational completion in the years since legalization. Given the many variables at work, the study will cast a wide net and will examine behavioral trends if they emerge.

Hewitt expects to begin recruiting sets of twins—some of whom he has studied in previous research—in January. He and Hopfer will collect data over five years, but expect to begin publishing preliminary findings within a year or two. Some of the subjects will be identical twins and others fraternal. Hewitt says studying both groups will allow the researchers to determine whether there’s a correlation between genetic makeup and cannabis-related behavior. If, say, the researchers find identical twins tend to have more similar responses to cannabis availability than fraternal twins do, that might indicate that the way legal cannabis impacts our lives is, at least in part, genetically determined.

“It’s probably not a lot different than you would have seen when you moved from prohibition to alcohol becoming available again,” Hewitt says. “You would expect that for many people it would be a neutral thing [legalization wouldn’t impact their behavior], for others, there’d be some benefit [to legalization] and for others, there’d be some adverse consequences.”

“Here we are in Colorado, with a major change in public policy toward marijuana that’s been in place for about three years and there’s really very little known about the consequences of that,” Hewitt says. “We just see a gap in our knowledge that we wanted to fill.” (The Colorado Department of Public Health and the Environment [CDPHE] does put together this annual report with existing research on the health impacts of cannabis, intended to monitor emerging health trends since marijuana became available for recreational use in 2014.) 

Ken Gershman, who manages the CDPHE Marijuana Research Grants Program (the agency was not involved in funding the CU study) expects Hewitt’s and Hopfer’s work to serve as a useful contribution to public knowledge of cannabis. “Although there is much existing research on the negative cognitive and mental health effects of MJ use, much of it pre-dates (recreational) MJ legalization,” Gershman wrote in an email. “…I think this study will contribute to and inform policy discussions.” 

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The fact that the study is funded by NIDA, a federal agency mandated to study substance abuse, has prompted skepticism  from other experts. Allen Shackelford, a physician, medical marijuana administrator, and CDPHE Medical Marijuana Research Grants Program board member, alleges NIDA has a history of funding studies that show controlled substances pose a high risk for abuse and/or negative health effects.  “NIDA has a history of funding studies that are intended to support their preconceptions about whether something is dangerous or not,” Shackelford says. 

A News21 analysis of the National Institutes of Health (NIDA’s parent agency) found that of the $1.4 billion of research funding awarded to study cannabis from 2008-2014, $1.1 billion was spent on examining abuse and addiction, and about $300 million went to study the potential medical benefits.

Hewitt says his research has no agenda and actually wouldn’t indicate a causal relationship between cannabis use and behavior or mood changes. By design, the study can only show correlation.  Based on Hewitt’s prior research on fraternal and identical twins and substance use, even that isn’t likely to be found. 

“What we often find in the kinds of studies we do is that actually both the twin who uses the substance and the one who doesn’t are equally likely to show the apparent consequence [of behavior or mood changes],” Hewitt says. “…we are probably in a better position to shoot down a causal relationship than we are to establish one.”

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