Despite the presence of state-regulated marijuana markets in more than half of all states in the U.S., kids now in middle school and high school report having a harder time finding marijuana than kids reported a decade ago, a new survey finds.

According to this year's Monitoring the Future survey, an annual questionnaire funded by the National Institute on Drug Abuse (NIDA), the number of eighth graders who say marijuana is easy to get has dropped to the lowest level since the study began tracking that age group in the 1990s. The percentages of 10th and 12th graders who said they could get their hands on marijuana has also declined.

One of the top four concerns of anti-legalization nonprofit Smart Approaches to Marijuana (SAM), which was co-founded by former Congressman Patrick Kennedy and a former White House drug policy advisor Kevin Sabet, is that legalization will increase children's access to marijuana and usage.

But since 1996, when California legalized medical marijuana, NIDA data shows that teens reported lower levels of availability to marijuana each year. In 1996, 54.8 percent of eighth graders reported it would be "fairly easy or very easy" to get marijuana if they wanted some. By 2006, that number decreased to 39.6 percent and in 2016 it dropped to 34.6 percent. For 10th and 12th graders, the downward trend is the same but older kids report having more availability than younger ones.

Tom Angell, the founder of pro-legalization organization Marijuana Majority, is pleased with the reported decrease.

"We've always argued that taking marijuana out of the unregulated criminal market and putting sales into the hands of responsible retailers would actually make it harder for young people to get," says Angell via email.

The NIDA study showed teen drug use and alcohol use has decreased from both last year's levels as well as peak use levels in the 1990s and 2000s. Marijuana use in 8th graders went down, but use for 10th graders and 12th graders has remained stable from last year. More high schoolers in legal states use marijuana than do high-school kids in non-legal states.

Kevin Sabet of SAM says that he believes legalization is why high school marijuana use has remained stable from last year and did not decrease like other drugs.

"Why would marijuana use not be falling like the use of other substances? The answer is likely marijuana commercialization and industrialization, spurred by legalization initiatives," Sabet said in a statement. "It also might explain why six percent of high school seniors use marijuana daily."