The number of U.S. parents talking to their teenagers about drugs has dropped, perhaps reflecting the more relaxed attitudes of a generation that came of age in the late 1970s when U.S. teen drug use peaked, a study on Tuesday found.

In 2004, about 12 percent of U.S. parents never talked to their children about drugs, twice the level recorded in 1998, said Steve Dnistrian, vice president of the Partnership for a Drug-Free America, which conducted the survey.

“This slippage worries us, because kids have got to hear about the problems of drug use from someone,” said Dnistrian.

Some experts believe the drug experiences of the parents make them less likely to see risk for their children.

U.S. parents of teens grew up in a time when more adolescents used marijuana than today. In 1979, 60 percent of high school seniors said they had tried marijuana, while only 46 percent of seniors reported trying pot in 2003, the study found.

“We are probably talking about drug survivors, so from their point of view, parents think, ‘What’s the big deal if kids try drugs?’” said Dr. Herbert Kleber, director of Columbia University’s Division on Substance Abuse, who was not associated with the study.

Kleber said the trend was worrying because today’s drugs can be stronger than those used in the 1970s.

Today’s marijuana can contain 12 percent or more of the mind-altering active ingredient tetrahydrocannabinol, or THC, compared with 1 to 3 percent in the 1970s, Kleber said.

“Children of today’s generation are more likely to get in trouble with drugs if parents don’t do something,” he said.

Parental attitudes toward drug experimentation were also changing, the study found.

Some 43 percent of parents said there was little risk from young people trying marijuana once or twice, compared with 35 percent sharing that view in 1998.

Similar experimentation with cocaine was seen as posing only a slight risk by 12 percent of parents, compared with 7 percent six years ago.