“Feeling down,” “Feeling irritable,” “Trouble getting up in the morning?” “Depression hurts,” “Drug X can help,” “Speak to your doctor about Drug X.” These 60-second appeals are an ubiquitous part of the U.S. television experience. This is because, in the U.S., pharmaceutical companies can lawfully market prescription medications to the public through direct-to-consumer (DTC) advertising. Critics have charged that doctors should decide prescription medications without being influenced by patient requests. Citing their proliferation as the main culprit for increasing patient demand for advertised drugs, the American Medical Association has advocated for a ban on DTC ads. But the pharmaceutical companies argue that patients have the right to know their options and thus benefit from these commercials. 

The ability to market prescription drugs creates an incentive for pharmaceutical companies to amplify the benefits of a drug without discussing its potential side effects. To counteract this, in the late 1990s the U.S. Food and Drug Administration regulated these ads by stipulating they present a fair balance between the benefits and risks (that is, side effects and contraindications) associated with a drug: the space in print media, and the airtime on broadcast media, allotted to listing its risks or side effects should be equivalent to the space and time allotted to its benefits. The assumption was that listing all side effects of a drug balances an inflated impression of its efficacy, allowing consumers to make an informed decision. 

But the FDA’s belief that more risk information leads to greater concern about risk is misplaced. Across six experiments, comprising more than 3,000 U.S. participants, we reliably found that when drug commercials included all side effects (both major and minor), in line with the FDA’s regulations, consumers judged the overall severity of the side effects to be lower than when they were exposed to only major ones. This lowered assessment of severity led consumers to prefer the drug more—and made them willing to pay more for it.

It is well established that people are susceptible to a range of cognitive and psychological biases that stray decisions from rationality. One such bias is the argument dilution effect. This bias is especially consequential when making social and nonsocial judgments about a target with an array of information that is both relevant and irrelevant to the decision. In such situations, our conclusions about the target are roughly based on averaging both the relevant and irrelevant information instead of ignoring the latter. In other words, the irrelevant information dilutes the value and importance of the relevant information. Initially documented by Richard Nisbett of the University of Michigan and his colleagues, the argument dilution effect’s ubiquity in impacting social and non-social judgments is well-established. For instance, imagine having to assess the grade point average of the following two students. You are either told, “Tim spends about 31 hours studying outside of class in an average week,” or, “Tom spends 31 hours studying outside of class in an average week. Tom has one brother and two sisters. He visits his grandparents once every 3 months. He once went on a blind date and shoots pool about once every 2 months.” When participants in a study by Henry Zukier, then at the New School for Social Research, were presented with these options, Tim was rated as having a significantly higher GPA than Tom. The irrelevant information around Tom’s grandparents and his casual play of pool, “diluted” the value and importance of the relevant information—his study habits. 

We wanted to know if the dilution effect also plays a role in DTC commercials. The FDA regulation to list all potential side effects of the drugs in a DTC commercial inadvertently resulted in these commercials describing both major (for example, stroke, heart-attack, thoughts of suicide) and comparatively minor (for example, dry mouth and headache) side effects. Building on argument dilution as the underlying psychological bias, we hypothesized that listing both major and minor side effects would dilute consumers’ judgments of the overall severity of the drug’s side effects, compared with when only major side effects are presented.

In one experiment, American participants heard an audio commercial for Cymbalta—a drug that treats depression and has been marketed via DTC advertising. Half of the participants heard the original commercial in its entirety (78 seconds), while the other half heard a 4 percent shorter commercial (75 seconds) that removed mention of the three minor side effects. Those who heard the commercial in its entirety rated the drug lower in its overall severity of side effects, compared with those who heard the 4 percent shorter version. In addition, the lower overall assessment of severity increased the attractiveness of the drug for that group in comparison with those who heard the shorter commercial. 

A follow-up study employed a different advertising medium by having participants read an actual print ad for the drug Lunesta, which is used to treat sleep disorders. Once again, half of the participants read the entire ad, which included four side effects (two major and two minor), while the other half read an ad that included just the two major ones. Again, reading the ad with more side effects, including minor ones, caused participants to rate the drug less in overall severity and more in appeal.

These findings raise the ethical and practical dilemma of achieving transparency with the consumers by sharing all potential side effects, while safeguarding them against argument dilution bias. Hence, we performed an additional study to explore how this might be achieved. If individuals can cognitively place greater weight to the major side effects than the minor ones, the averaging process of the argument dilution effect, should attenuate. Thus, to draw greater attention and emphasis to the major side effects, we listed them in a red boldfaced font and set minor ones in a black regular font. Participants who saw major and minor side effects in different fonts rated the drug similar in severity, compared with those who only saw the major side effects. So by drawing greater attention to the major side effects, we were able to overcome the argument dilution effect while ensuring that all side effects associated with the drug were communicated to consumers.

With the industry annually spending billions of dollars on DTC ads, it is not surprising that they have resulted in increased patient demands for the drugs featured in them. These results add to the chorus for the redrafting of policies surrounding the communication of pharmaceutical drugs’ risk. More broadly, this work draws caution to other forms of risk communication that extends beyond DTC: from physicians who have to communicate varying risks of an experimental procedure, to financial advisors who need to make retirees aware of different perils in the financial products they intend to invest in, to public service advertisements that attempt to highlight the risk associated with life choices.