Antismoking ads produced by the tobacco industry not only don't prevent youth smoking but sometimes actually encourage teens to smoke, according to researchers who studied more than 100,000 teens.

Reuters reported Oct. 31 that researchers examined viewer data from Neilsen Media Research to gauge the impact of industry-sponsored ads on 12- to 17-year-olds in the 75 largest U.S. media markets, alongside surveys on tobacco use among 8th-, 10th-, and 12th-graders. They found no relationship between how frequently the ads were viewed and youth attitudes about smoking.

"This research provides the clearest evidence to date that tobacco-sponsored ads don't work," said lead researcher Melanie Wakefield of the University of Illinois. "Tobacco-sponsored ads targeted at youth have no impact, and those targeted at parents seem to have an adverse effect on students who are in their middle and later teenage years."

Wakefield suggested that ads telling teens not to smoke because their parents don't want them to is a case of the tobacco industry using reverse psychology.

Researchers cited ads like Philip Morris' "Think. Don't Smoke" and Lorillard's "Tobacco is Whacko if You're a Teen" as examples of ineffective campaigns, and noted that a prominent tobacco executive said that the aim of the ads is not to prevent smoking but merely delay it to age 18.

Peggy Roberts, a spokeswoman for Philip Morris, said, "We haven't found anything (in our research) to indicate that this study's conclusions are valid."

The study was published Oct. 31, 2006 in the advance online edition of the American Journal of Public Health.