Use of two of the most deadly and addictive substances known to man is on the downswing among American teens as they increasingly turn to marijuana, a study published Thursday claimed.

Among high school seniors, marijuana use is at a 30-year high, with 1 in 15 saying they use the drug near daily, according to an annual survey of about 50,000 teens in grades 8, 10 and 12. About a quarter of teens surveyed said they tried marijuana at least once last year, and 50 percent overall said they had used an illegal drug before.

Funded by the National Institute on Drug Abuse (NIDA), Michigan University's yearly "Monitoring the Future" (PDF) report also found that alcohol abuse, which the Centers for Disease Control says kills more young Americans than any other drug, is also at a historic low.

Tobacco use, similarly, has gone down by a statistically significant amount: just 11.7 percent of U.S. teens say they've smoked a cigarette in the last 30 days, compared to 12.8 percent in 2010.

The study also found that most teens don't view marijuana as a dangerous drug, which lends itself to usage rates going up. While it is impossible to overdose on marijuana and the intoxicating effects are often less disruptive than alcohol, it can promote apathetic and gluttonous behaviors, and long-term smoking can lead to an assortment of lung diseases. There's also strong evidence that people genetically predisposed to schizophrenia might be at risk for intensifying paranoid delusions after using marijuana.

However, Gil Kerlikowske, who directs the Office of National Drug Control Policy, attributed the rise in use to the growing availability of medical marijuana, which is only sold to adults with valid forms of identification and a doctor's recommendation in the 16 states where its legal.

"We know that any substance that is legally available is more widely used," he said.

That claim, which was not specifically supported by the research, was seemingly undermined recent data released by the Institute for the Study of Labor, which sought to answer that question but found no evidence that the availability of medical marijuana drove teens' usage habits.

It did find, however, that marijuana use was up among adults in states where it has been approved by voters. The same figures also found that more adults were using marijuana instead of drinking alcohol, which cut into the overall number of traffic fatalities due to drunk driving -- a trend which also shows up in Thursday's "Monitoring the Future" report.

Photo: Flickr user Bob Doran.