Resarchers from New York University, Tel Aviv University, and INSEAD in Singapore explored how these warnings affect consumer decisions and published their findings in the journal Psychological Science.
"We were struck by just how detailed, clear, and scary many warnings had become with regard to potential negative side-effects of products," said Ziv Carmon of INSEAD. "It then occurred to us that such warnings might perversely boost rather than detract from the appeal of the risky product."
Researchers conducted four experiments using ads for cigarettes, artificial sweeteners, and drugs for erectile dysfunction and hair loss.
They found that when there is a delay between viewing the ad and deciding to buy or consume the product, sales increased.
Smokers predictably bought fewer cigarettes immediately after seeing the ad with the warning that smoking causes lung cancer, heart disease, and emphysema.
But participants who were given the opportunity a few days later bought more if the ad included the warning. Researchers found the same result with artificial sweeteners.
"Messages that warn consumers about potentially harmful side effects -- presumably with the intent to nudge them to act more cautiously -- can ironically backfire," Carmon said.
Researchers say the psychological distance created by a delay between ad exposure and consumer decision made the side effects seem abstract, and participants instead considered the warnings an indication of a company's honesty and trustworthiness.
Participants who evaluated drugs for erectile dysfunction and hair loss that had potentially serious side effects actually saw them more favorably, and as more trustworthy, when they were told the products weren't on the shelves yet.
Side effect warnings in drug ads have become so ubiquitous that researchers believe their potential to backfire is a serious health issue.
"This effect may fly under the radar since people who try to protect the public -- regulatory agencies, for example -- tend to test the impact of a warning shortly after consumers are exposed to it," says Carmon. "By doing so, they miss out on this worrisome delayed outcome."