Illicit drug use by teens continued to gradually decline overall this year, but the use of prescription painkillers remains popular among young people, according to a federally financed study released Tuesday at the White House.

The survey, by the University of Michigan's Institute for Social Research, looked at the behavior of 8th, 10th and 12th graders nationwide.

The proportion of 8th graders reporting use of an illicit drug at least once in the 12 months prior to the survey was 24 percent in 1996. It now has fallen to 13 percent — a drop of nearly half.

Among 10th graders, the rates dropped from 39 percent to 28 percent between 1997 and 2007. Twelfth graders saw a decline from a peak of 42 percent in 1997 to 36 percent this year.

"The cumulative declines since recent peak levels of drug involvement in the mid-1990s are quite substantial especially among the youngest students," said Lloyd Johnston, the principal investigator of the study, which was financed by the National Institute on Drug Use. It surveyed 50,000 teens.

The drugs most responsible for this year's decline in illicit drug use are marijuana and various stimulants, including amphetamines, methamphetamine and crystal methamphetamine.

"The most encouraging statistic relates to the use of methamphetamine, which has plummeted by an impressive 64 percent since 2001," President Bush said.

"One exception to this trend is a rise in the abuse of certain prescription painkillers," Bush said. "This is troubling, and we're going to continue to confront the challenge and the overall direction is hopeful."

At least one in every 20 high-school seniors has at least tried OxyContin, a powerful narcotic drug, in the past year, the study said. The popularity of the painkiller Vicodin also remained constant. The percentage of students using Vicodin was 2.7 percent, 7.2 percent and 9.6 percent in 8th, 10th and 12th grades, respectively.

While the use of most illicit drugs has shown declines in the past decade or so, most prescription psychotherapeutic drugs did not. A number of them showed steady increases in use outside of their legitimate medical purpose. These include sedatives, tranquilizers and narcotic drugs other than heroin.

The study also reported an increase in the use of ecstasy. Ecstasy use among teens dropped dramatically in the early 2000s, as concern about the consequences of use grew. However, the proportion of students seeing great risk in using this drug has been in decline for the past two or three years at all three grade levels, and use has begun to increase, at least in the upper grades.

Among 10th graders, annual prevalence has risen from a recent low of 2.4 percent in 2004 to 3.5 percent in 2007, while in 12th grade it has risen from a recent low of 3 percent in 2005 to 4.5 percent in 2007. While none of the one-year increases were statistically significant for 2007, a clear pattern of gradually rising use is discernible in the upper grades; and their cumulative increases over the past couple of years are statistically significant.

"These prevalence rates are not very high yet, but there is evidence here of this drug beginning to make a comeback," Johnston said. "Young people are coming to see its use as less dangerous than did their predecessors as recently as 2004, and that is a warning signal that the increase in use may continue."

Among the study's other findings:

_Amphetamine use peaked in the mid-1990s among eighth and 10th graders, but since then, use has fallen by more than one-half among 8th graders to 4 percent and by one-third among 10th graders to 8 percent this year. Amphetamine use peaked a little later among 12th graders and has fallen by about one-third to 8 percent this year.

_Use of methamphetamine, called "meth," has been declining since it was first measured in 1999. Annual prevalence is now down by about two-thirds in all three grades from what it was in 1999.

_Marijuana still remains the most widely used of all the illicit drugs. The decline in 2007 in the annual prevalence of marijuana use among 8th graders fell from 11.7 percent in 2006 to 10.3 percent in 2007. Tenth graders showed a modest continuing decline in marijuana use, while 12th graders showed no further change this year after a significant decline in 2006.

_The study tracked a fairly sharp increase in the use of anabolic steroids by male teens in the late 1990s, 2000, 2001 and 2002. Since those peak years, the annual prevalence rate has dropped by more than half among the 8th and 10th grade males — to 1.1 percent and 1.7 percent, respectively — and by 40 percent among 12th-grade males to 2.3 percent this year.

_The number of U.S. teens who smoke has shown significant declines in recent years, particularly among those in their early teens. The rate of teens who reported smoking in the 30 days before the survey is now down by two-thirds among 8th graders to 7 percent from the peak level reached in 1996 of 21 percent.

The study, titled Monitoring the Future, is in its 33rd year. It tracks smoking, drinking and illicit drug use among the nation's secondary school students, surveying about 50,000 8th, 10th and 12th graders in more than 400 secondary schools every year.