Fewer adolescents think smoking pot is risky than a decade ago, but the use of other drugs, including "bath salts," Ecstasy and tobacco, dropped in the same period, according to an annual nationwide survey.
The Monitoring the Future survey, funded by National Institute on Drug Abuse, has measured drug use and attitudes among 12th-graders for 38 years and among eighth- and 10th-graders since 1991.
For the first time, the percentage of students in all three grades who said they smoked a cigarette in the last month was under 10%. That compares with 16.7% in 2003 and 24.7% in 1993. And daily smoking was at 8.5% for seniors, 4.4% for sophomores and 1.8% for eighth-graders.
The survey reported that 39.5% of 12th-graders see regular marijuana use as harmful; that's down from 44.1% last year, and lower than the rates from the last two decades. Those numbers are troubling to the institute because previous survey data shows an association between "softening attitudes and increased use of marijuana," the agency said.
As for marijuana use, 6.5% of high school seniors said they smoked it daily in the last year, compared with 6% in 2003 and 2.4% in 1993. Nearly 23% of seniors said they had used pot in the month before the survey, and about 36% said they'd smoked it in the last year.
Among 10th-graders, 4% reported daily use, 18% in the previous month and 29.8% in the last year. And among eighth-graders, more than 12% said they used it in the previous year, according to the survey.
"The number that concerns me in particular is the rate of daily or near daily use," said Dr. Wilson Compton, deputy director of the National Institute on Drug Abuse, a part of the National Institutes of Health. "This rate is as high as we've seen since the early '80s."
Dr. Nora Volkow, the drug abuse institute's director, noted that over the last 20 years marijuana has gotten more potent, giving daily use "stronger effects on a developing teen brain than it did 10 or 20 years ago."
Volkow said in a statement: "The children whose experimentation leads to regular use are setting themselves up for declines in IQ and diminished ability for success in life."
The survey doesn't give researchers information to explain why, Compton said.
"Our issue around marijuana is a gradual undermining of social disapproval and a perceived harmfulness" of its use, he said in an interview.
And it's hard to draw conclusions from survey questions about attitudes to explain why teenagers do something.
"We can't draw a neat a line between the attitudes and the actions. What motivates an adolescent to use drugs is a variety of factors -- their background, what their friends are doing and what they perceive their friends are doing," Compton said.
States that have legalized marijuana use, recreationally or for medical use, may play a role, he said. "It certainly creates a false sense of safety and social acceptance that can be worrisome in terms of being associated with increased rates of use," Compton said.
The Marijuana Policy Project, an advocacy group, responded to the survey with a call to investigate whether regulating marijuana the way alcohol and cigarettes are regulated could lead to declines in use among teenagers.
"The results suggest that regulating alcohol and cigarettes is successfully reducing teen use, whereas marijuana prohibition has been unsuccessful," Mason Tvert, a spokesman for the Marijuana Policy Project, said in a statement.
Compton said the survey had good news, too.
It showed that 7.4% of 12th-graders took Adderall, prescribed for attention deficity hyperactivity disorder, for nonmedical reasons. But only 2.3% did so with another such drug, Ritalin. And the abuse of the pain reliever Vicodin has fallen from 10.5% in 2003 to 5.3% in 2013.
Decreases were also seen, the survey said, in the abuse of cough medicines, K2 or Spice, the stimulant called bath salts and inhalants. Use of Ecstasy peaked in 2001 among seniors at 9.2%, and 4% reported using it this year. Changes in heroin and cocaine use were statistically insignificant, but the totals were at all-time lows in all three grades, the survey said.
"We can't tell you what is causing those drops but it is certainly good news," Compton said. Compton said he would not conclude that adolescents were substituting marijuana for other drugs.
The use of alcohol continued to decline, the survey showed, with 39.2% of seniors reported drinking in the last month, compared with 52.7% in 1997, the peak year.
One negative note on tobacco, Compton said, was that 21.4% of seniors reported smoking tobacco through a hookah in the last year, 3% more than reported that a year ago. The survey did not ask about e-cigarettes, which contain fewer chemicals than traditional cigarettes and have been touted for not releasing smoke into the air.
Officials focused on the marijuana results.
"These increases in marijuana use over the past few years are a serious setback in our nation's efforts to raise a healthy generation of young people," the director of National Drug Control Policy, Gil Kerlikowske, said in a statement.
In 2012, the survey added questions about where students get marijuana. About a third of the 12th-graders in states with medical marijuana laws said they have gotten it with someone else's prescription, and 6% said they had a prescription.
Additional research is needed, Compton said, to determine the role that storefront marijuana shops like those found in Los Angeles play in attitudes and behaviors, as well as changes to its legal status.
The survey included 41,675 young people from 389 public and private schools. It was conducted by researchers at the University of Michigan. It's one of three major surveys sponsored by the federal government to gauge substance abuse among youth.