To protect patients, the Food and Drug Administration requires that direct-to-consumer drug advertisements present a fair balance of information about a drug’s potential benefits and its risks. As such, the ads seen on television or in magazines often contain an almost comically long list of possible side effects—from minor issues, like headaches or dry mouth, to serious problems, like memory loss, liver damage, or compulsive gambling.

On the surface, any such rundown might seem like a deterrent to trying a new drug. But, according to a new study, a laundry list of risks can make drugs appear less risky—the longer, the better, in fact.

In a series of experiments involving more than 3,000 participants, researchers found that when drug ads clumped severe risks alongside trivial ones, consumers viewed the drugs as less risky compared with when they just heard about the severe risks.

“Thus, listing all frequent side effects, both major and minor, does not dampen the drug’s attractiveness, but paradoxically increases it,” the behavioral researchers, Niro Sivanathan and Hemant Kakkar of London Business School, concluded. They reported their results Monday in Nature Human Behaviour.

Essentially, the pair argue, the inclusion of lots of trivial risks watered down the effect of hearing the severe ones—a psychological phenomenon called ‘the dilution effect.’ This comes into play when a person is evaluating an array of information. During the assessment, information of little value can distract and dilute the value of important information.

The effect also fits with the “fuzzy-trace theory,” according to behavioral researcher Brian Zikmund-Fisher of the University of Michigan. In an accompanying editorial, Zikmund-Fisher notes that the fuzzy-trace theory suggests that people process information to get a “core gist.” A long list of side effects, including both trifling and terrifying ones, may simply translate to an overall, emotionless gist of “this drug has a variety of risks” to consumers, he explains.

Regardless of the psychological explanation, the study’s results clearly “underscore the unintended consequences of current advertisements,” Sivanathan and Kakkar conclude. And they have a fix for it.

Risky twist

For the study, the researchers first recruited 804 participants who all listened to a real audio commercial for Cymbalta, a drug given to treat depression. Half the participants heard the full 78-second ad. The other half listened to a 75-second clip that omitted some of the minor side effects. Afterward, those who listened to the full commercial rated the drug as having fewer severe side effects than those who heard the shorter clip.

An obvious explanation might be that those listening to the full ad simply didn’t pay close attention to the longer list of side effects. But the researchers ruled that out. In fact, in a follow-up survey, the group that listened to the full ad did better at remembering the severe side effects than the group that listened to just those side effects. But, of those who heard just the severe side effects, the more of those side effects they remembered, the riskier they deemed the drug.

In a three-part experiment—each containing around 400 participants—the researchers tested variations of this experiment. They evaluated the shortened side effect list in: a paper advertisement for the sleep-disorder drug, Lunesta; a Drug Facts Box for the depression drug, Abilify; and text from an ad for Concerta, given to treat attention deficit hyperactive disorder. They also replicated the original experiment with a different group of another 400 participants, who read side effect information about the hypothetical insomnia drug, Xylopinol.

In all cases, drugs were seen as riskier when the participants only saw information on the most serious side effects, rather than the full list.

In the last experiment, involving around 600 participants, the researchers again replicated this ‘dilution effect’—then reversed it. They broke the group into three sections and again provided side effect information for the fictional Xylopinol. The first group got a full list, the second got just the serious side effects, and the last got an emphasized list. Specifically, the text for the serious side effects were in a bolded, 14-point red text while the minor side effects were in a 12-point, regular black text.

They reasoned:

If dilution is the result of averaging all side effects listed, it is plausible that the process is dampened if participants can cognitively isolate major and minor side effects, by assigning greater emphasis/weight to major and less emphasis/weight to minor side effects when evaluating the overall severity of side effects.

The hypothesis held up: participants who saw the weighted side effects considered the drug just as risky as the participants who saw just serious side effects. Those who saw the full list rated the drug as less risky.

Together, Zikmund-Fisher concludes that “this work suggests that the inclusion of more information, especially if it is unfiltered, can actually be counterproductive.” But, separating out the categories of risks may “ensure that patients consider the severity of possible negative outcomes, not just be aware that they might occur.”

Nature Human Behaviour, 2017. DOI: 10.1038/s41562-017-0223-1 (About DOIs).