A new study concludes teens’ perception of the dangers of marijuana is at its lowest level in more than 20 years, prompting federal researchers to warn that the already high use of the drug could increase as more states move to legalize it.

The annual survey released Wednesday by the National Institutes of Health found that only 41.7 percent of eighth graders believe occasional use of pot is harmful. Roughly 44.1 percent believed that its regular use was detrimental, the lowest rate since 1979.

The government-sponsored study said teens' dwindling concerns about the dangers of marijuana, despite the risks, “can signal future increases in use.”

“We are increasingly concerned that regular or daily use of marijuana is robbing many young people of their potential to achieve and excel in school or other aspects of life,” said Dr. Nora D. Volkow, director of the National Institute on Drug Abuse, which is part of NIH. She said teens are influenced by whether a drug is legal in some form when deciding to try it recreationally, so in states where marijuana is sanctioned, “the deterrent is no longer present.”

Volkow cited recently published research showing that people who used marijuana heavily before age 18 had impaired mental abilities even after they quit using the drug. According to the studies, those who used cannabis heavily in their teens are into their adulthood showed a significant drop in IQ between the ages of 13 and 38.

“Marijuana use that begins in adolescence increases the risk they will become addicted to the drug,” said Volkow.

The findings come after Washington and Colorado voted November to legalize marijuana and regulate its recreational use, boosted by the strong support of younger voters. While the new laws apply only to adults over 21, the broader effort by states to decriminalize pot use and push the drug toward public legitimacy could confuse the picture for teens.

“Now more than ever we need parents and other adult influencers to step up and have direct conversations with young people about the importance of making healthy decisions,” said White House drug czar Gil Kerlikowske Wednesday.

The federal survey states marijuana use among teenagers remained stuck at high levels in 2012. Roughly 6.5 percent of 12th graders smoked marijuana daily, up from 5.1 percent in 2007. About 45 percent of high school seniors reported they tried marijuana at least once in their lifetime.

In a 2011 national survey, it showed teenage Latino males are more likely to “regularly use” marijuana than Latinas. While average marijuana use among teens increased from 2010 to 2011, there was nearly a 10 percent reduction among Latino males.

Based on reporting by The Associated Press.

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