Regular marijuana use among Colorado teens has fallen to its lowest level in a decade, according to new federal numbers.  And rates of teen alcohol, tobacco and heroin use are also down sharply in the state since the state legalized cannabis use for adults.

The National Survey on Drug Use and Health, conducted in 2015 and 2016, showed just 9 percent of Colorado youths aged 12 to 17 reported using marijuana in the month prior to being surveyed. That compares to 11.13 percent during the prior two years.

The study also showed a small drop in teen cannabis in Washington state, and basically no change in other states where marijuana has been legalized. The data runs counter to claims by many marijuana legalization opponents that the laws would lead to increased teen drug.

“These survey results should come as welcome news to anyone who worried teen marijuana use would increase following legalization,” Brian Vicente, a Denver lawyer specializing in cannabis policy, said in a statement quoted by The Denver Post.

Larry Wolk, the executive director of the Colorado Department of Public Health and Environment, told The Post the new numbers offer a glimmer of reassurance that regulations designed to keep marijuana out of the hands of kids and teens is working. Still, he said a better understanding of cannabis use among Colorado’s youth will come next spring when the state completes its own more thorough study.

The last state study, released in the summer of 2016, showed rates of marijuana use among Colorado’s teenagers remained essentially unchanged since voters legalized marijuana in 2012.

With the latest federal numbers, Colorado falls to No. 7 in the national ranking of teen marijuana use, behind Alaska, Maine, New Mexico, Oregon, Rhode Island and Vermont.