A new study confirms a growing body of research that shows a drop in illegal drug use among American teenagers, which has some media outlets attributing the legalization of pot to the downward trend.

The 2014 Monitoring the Future study, conducted by the University of Michigan and the National Institutes on Drug Abuse, surveys 40,000 eighth, tenth, and twelfth-graders each year on their use of substances. The results showed marked declines in the use of marijuana, alcohol, prescription drugs, and even cigarettes among these groups on both a monthly and daily basis.

The findings are in accordance with the results of a similar study conducted earlier this year by the National Survey on Drug Use and Health. The authors of the Monitoring the Future study summarized their findings by stating, “Both alcohol and cigarette use in 2014 are at their lowest points since the study began in 1975. National Institutes of Drug Abuse director Nora D. Volkow added that with the use of marijuana appearing to either level off or fall in 2014, “it is possible that prevention efforts are having an effect.”

While the flatline status of marijuana use in a year marked by relaxed legal status for medical and recreational use of the drug is notable data, not every substance appeared to be in decline among teens. Heroin use remains stable among teenagers, while e-cigarette use showed a marked increase among the study focus groups. And while binge-drinking dropped to 12%, one in five high school seniors reported that they still indulged in it.

“Even though the indicators are very good news, at the same time, we cannot become complacent,” said Volkow. “This is a stage where [teenagers’] brains are most vulnerable. We need to continue our prevention efforts."