with previous research on identical twins revealing that those who lived in states with legal access to the drug used it 20 per cent more often, the team hoped to parse out any potential problems associated with use. this included comparing surveys from twins that evaluated 23 measures of “psychosocial distress,” including the use of alcohol and illicit drugs (such as heroin or cocaine), psychotic behaviour, financial or cognitive problems, unemployment and interpersonal relationships.
“we included everything we had data on with the goal of getting a well-rounded look at the impacts on the whole person,” zellers said. “big picture, there’s not much there.”
in addition to finding no relationship between the legalization of marijuana and an increased risk of cannabis use disorder or addiction, researchers found no evidence the substance acted as a gateway to more harmful drugs. there was no change in illicit drug use following the legalization of marijuana.
“for low-level cannabis use, which was the majority of users, in adults, legalization does not appear to increase the risk of substance use disorders,” said christian hopfer, co-author of the study and a medical doctor and professor of psychiatry at ibg and cu anschutz who studies substance abuse disorders.
on the contrary, they found that twins living in states with legalized marijuana displayed fewer symptoms of alcohol use disorder and were less likely to engage in risky behaviour — such as driving under the influence — after drinking.
“our study suggests that we should not be overly concerned about everyday adult use in a legalized environment, but no drug is risk-free,” hewitt said. “it would be a mistake to dismiss the risks from higher doses of a drug that is relatively safe in small amounts.”
although the study had a few limitations, including a failure to examine the health impacts of the drug on adolescents or examine the types and doses of cannabis used, the team hopes its results will help inform public policy and general discussion on the merits of legalization.