Teens are using marijuana less, and some even disapprove of it more, according to a new study from the University of Texas at Austin School of Social Work.

Contrary to what some legalization opponents have insisted—that broader access to medical marijuana would increase rates of use and acceptance among impressionable adolescents—the research shows that the substance's popularity is actually faltering.

"Changes were particularly marked among younger adolescents (ages 12-14), as study findings point to a 25 percent decline in the relative proportion of youths reporting marijuana use in the previous 12 months, and an increase from 74 percent to 79 percent reporting strong disapproval of marijuana use initiation," researchers determined.

This study, published in The American Journal of Drug and Alcohol Abuse this month, looked at youth use and perception trends between 2002 and 2013, drawing from self-reported questionnaires and representative data provided by the National Survey on Drug Use and Health. Researchers differentiated between age cohorts—12 to 14, 15 to 17, and 18 to 25—and were surprised by what they found.

While disapproval rates for marijuana were remarkably high among the youngest age bracket, older groups surveyed for the study also showed signs of growing disinterest in the substance. Those aged 15-17 report that they don't use marijuana as much anymore; asked whether they've consumed cannabis within the past 12 months, about 22 percent affirmed—down more than four percent since 2002.

"Our results may suggest that recent changes in public policy, including the decriminalization, medicalization, and legalization of marijuana in cities and states across the country, have not resulted in more use or greater approval of marijuana use among younger adolescents," the study's co-author Christopher Salas-Wright told UT News. In fact, the opposite appears to be true.

Michael Vaughn, another co-author and a professor of social work at St. Louis University's College for Public Health and Social Justice, said that "[r]ecent policy changes and increasing exposure to marijuana as perhaps normative or no longer immoral may be influencing how young adults feel about others using marijuana, but not necessarily impacting their own use."

Some form of marijuana—medical or recreational—is now legal in 23 states, plus the District of Columbia. Four of those have legalized marijuana for recreational purposes. For years, opponents have argued that the proliferation of the cannabis industry would inevitably lead children to experiment—to feel more comfortable around the substance based on their perceptions about its growing public acceptance. But that theory falls short of the research findings here, suggesting that fears about the youth response to legalization may be totally unwarranted.