The annual National Survey on Drug Use and Health estimates that 6.8 percent of middle school and high school students used marijuana in 2005, down from 7.6 percent the year before.
John P. Walters, head of the White House Office of National Drug Control Policy, heralded the news as a sign of "a cultural change" in which American teens are slowly turning away from drug use.
Walters also pointed to a drop in the number of first-time users of methamphetamine, a highly addictive stimulant that has torn at many rural and Western communities. Methamphetamine use appears to be shrinking, he said.
But the survey also shows Americans' use of illegal drugs has changed little since 2002.
Apparent improvement in the 12- to 17-year-old age group was offset by stagnation or increases in drug use in other age groups. Americans' overall drug use in 2005 actually ticked up slightly from 2004, the survey shows.
An estimated 20 million Americans, or 8 percent of the population 12 years or older, reported using illegal substances within the past month, according to the survey.
One problem group appears to be baby boomers, whose use of drugs such as marijuana and painkillers has risen slowly but steadily in the last four years.
Also, one-fifth of all 18- to 25-year-olds reported using illegal drugs in the past month, a figure nearly identical to 2002.
The overall number of meth users nationwide also did not change, according to the report.
The survey sampled nearly 68,000 Americans aged 12 and older.
In alcohol and tobacco use, there was also little progress. Those drugs are responsible for the vast majority of drug-related injuries and deaths in the U.S.
More than 29 percent of Americans aged 12 or older reported using tobacco in the last month.
And 28 percent of those aged 12 to 20 (10.8 million people) acknowledged drinking in the past month. That number has stayed about the same since 2002, the survey notes.
SOURCES: "National Survey on Drug Use and Health: National Findings 2005," Sept. 7, 2006. John P. Walters, director, White House Office of National Drug Control Policy.
By Todd Zwillich
Reviewed by Louise Chang