Former US Marine Sgt. Ryan Begin rolls a medical marijuana joint at his home in Belfast, Maine. (Image via AP Photo/Robert F. Bukaty)

A big boost for medical marijuana advocates: A massive study involving data on a million teenagers in 48 states has found no evidence that legalizing pot for medical use does anything to increase teen usage, the Guardian reports.

The study, published in the Lancet Psychiatry journal, looked at some 1,098,270 8th-grade, 10th-grade, and 12th-grade students over 24 years; the teens had been asked if they used pot in the last 30 days. The researchers found that teenage pot use not only failed to rise in the 21 contiguous states where medical marijuana was legalized as of 2014 (Alaska and Hawaii bring the nation’s total to 23), usage actually went down among the youngest teenagers, from about 8% before the law was passed to 6% after.

In states that brought in medical marijuana laws, teen pot use was already slightly higher than in other states, at about 16% usage to 13%. Experts say that could be due to a more liberal general attitude toward the drug, LiveScience reports.

“Our study findings suggest that the debate over the role of medical marijuana laws in adolescent marijuana use should cease, and that resources should be applied to identifying the factors that do affect risk,” the researchers wrote. As for why pot use fell among 8th graders after it was legalized for medical purposes, here’s one theory: that the teens started to see marijuana as a relatively harmless medical product, which “certainly doesn’t fit with the idea of being a rebellious teenager,” writes Debra Borchardt at Forbes. (A separate study tracked the pot “use” of kids—under age six.)

By Rob Quinn

More From Newser.com:

Couple’s Babymoon Now a Nightmare

Study Has Bad News for Teen Potheads

Your Earwax Says a Lot About You

Widow Says Pedicure Killed Her Husband

A 27-Year-Old Has Given Birth in a Historic Way

This article originally appeared on Newser: Here’s How Legalizing Pot Affected 1M Teens