Teen smoking and drinking continued to drop, but teenage abuse of prescription drugs has become "an entrenched behavior" that many parents fail to recognize, a survey released Tuesday showed.

For a third straight year, the Partnership for a Drug-Free America study showed that about 1 in 5 teens have tried prescription drug painkillers such as Vicodin or OxyContin to get high — about 4.5 million teens. It also indicated that many teens feel experimenting with prescription drugs is safer than illegal highs.

Forty percent said prescription medicines were "much safer" than illegal drugs, while 31 percent said there was "nothing wrong" with using prescription drugs "once in a while." The study further found that 29 percent of teens believe prescription pain relievers are non-addictive.

"It's really a case now of accepting the fact that it's here," Partnership President and CEO Steve Pasierb said. "Clearly, this is a true problem in American society."

Although this was the group's 18th annual survey, it marked only the third year of compiling figures on the abuse of legal drugs. In 2003, the study found 20 percent of teens had tried the prescription drugs Vicodin, OxyContin and Tylox. Over the next two years, the numbers remained fairly consistent.

Pasierb said it was a good sign that the prescription drug numbers had not increased, but warned parents that the source of drugs is now the family medicine cabinet more than any dealer. The study found 62 percent of teens said prescription pain relievers are easy to find at home. And 52 percent say prescription pain relievers are "available everywhere."

"That's why we're putting a lot of our attending on educating parents," Pasierb said. "They don't have a frame of reference in a lot of cases. This kind of behavior [prescription drug abuse] didn't exist when they were teens."

A study by the University of Michigan, released in December, also indicated that American teens were smoking less and using prescription drugs more. It found 1 in 10 high school seniors had experimented with prescription painkillers.

The Partnership survey put teen smoking at 22 percent, down from 23 percent last year and 42 percent in 1998. The number of teens drinking in the past 30 days was down from 33 percent last year to 31 percent; in 1998, the figure was 42 percent.

The 2005 Partnership Attitude Tracking Study surveyed more than 7,300 teens in grades 7 through 12, the largest ongoing analysis of teen drug-related attitudes toward drugs in the country. Its margin of error was plus or minus 1.5 percentage points.

The nonprofit Partnership for a Drug-Free America was launched in 1987.