As marijuana legalization spreads across the United States, opponents have maintained that there will be negative long-term consequences, especially on young people. But new federal data says pot use among teens aged 12-17 is actually dropping in states that allow recreational marijuana use.

The National Survey on Drug Use and Health, an annual nationwide survey, found declines in teen marijuana use in all but one of the five states that had legal weed from 2014 to 2016.

Colorado sold more than a billion dollars worth of weed last year, but the number of teens who reported smoking pot in the past year there dropped from around 18 percent to 16 percent, with a similar drop — from 11 percent to 9 percent — in teens reporting they’d smoked in the past month.

Other states saw similar declines or no major change in yearly use, including Washington, D.C. (16 percent to 13 percent), Oregon (17 percent to 17 percent), and Washington state (15 percent to 13.5 percent), while underaged smoking ticked up just barely in Alaska (18.44 percent to 18.86 percent).

It’s still unclear why this is happening. It could be that teens are deciding that smoking weed is uncool because they’re seeing their parents do it, or it could be that states with recreational marijuana laws often employ public health campaigns designed to discourage young people from getting high. Or maybe it’s something else entirely.

It's also not true among all age groups. As anti-legalization activist Kevin Sabet points out, weed use among young adults 18-25 has increased since 2014, according to the National Survey on Drug Use and Health.

The federal data jibes with academic research on the issue of teen drug use. A forthcoming study in the journal “Drug and Alcohol Dependence” concluded that the enactment of state medical marijuana laws “is associated with decreases in marijuana and other drugs in early adolescence in those states.”

Still, the facts haven’t stopped prohibition advocates like Sabet, the founder and president of the organization Smart Approaches to Marijuana, from insisting that legalization will be harmful to children. (Also on Monday, he agreed with another Twitter user who claimed that citing a year-over-year downward trend in teen marijuana use is “the same logic used by climate change deniers any time there is a winter slightly colder than the year before.”)

Sabet is an influential figure in the world of drug policy. Just last week, he and other prohibitionists had a private meeting with Attorney General Jeff Sessions, who has ordered a review of the Trump administration’s policy on federal marijuana law enforcement.

“It’s my view that the use of marijuana is detrimental and we should not give encouragement in any way to it,” Sessions said in late November. “And it represents a federal violation which is in the law and is subject to being enforced, and our priorities will have to be focused on all the things and challenges that we face.”