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BOULDER, Colo. (KDVR) — Legalizing cannabis does not increase substance use disorders or use of other illicit drugs, and therefore is not considered a “gateway drug,” according to a new study from the University of Colorado Boulder.

The study, published on Jan. 5 in Psychological Medicine, said that despite many critics of legalization expressing concerns that cannabis is a gateway drug, research found no changes in illicit drug use after legalization. Instead, it may actually reduce alcohol-related problems.

According to CU, the study also found no link between legalization and cognitive, psychological, social, relationship and financial problems.

“We really didn’t find any support for a lot of the harms people worry about with legalization,” said lead author Stephanie Zellers, who began the research as a graduate student at CU Boulder’s Institute for Behavioral Genetics. “From a public health perspective, these results are reassuring.”

Where CU gathered the data from

Researchers from CU Boulder, the University of Colorado Anshutz Medical Campus and the University of Minnesota took data from the Institute for Behavioral Genetics and the Minnesota Center for Twin Family Research to study 4,000 twins.

The twins came from Colorado, which was one of the first states to legalize marijuana, and Minnesota, where recreational use remains illegal.

Researchers found that identical twins living in states where cannabis is legal used it 20% more frequently. However, when they compared results and looked at cannabis use disorder, use of alcohol and illicit drugs, and psychotic behavior, the research found no relationship to legalization.

“Our study suggests that we should not be overly concerned about everyday adult use in a legalized environment, but no drug is risk-free,” said co-author John Hewitt, professor of psychology and neuroscience at CU Boulder. “It would be a mistake to dismiss the risks from higher doses of a drug that is relatively safe in small amounts.”

Additionally, the research found that twins who lived in cannabis legal states showed fewer symptoms of alcohol use disorder.

Currently, there are 21 states that have legalized recreational cannabis.