The unintended consequences of argument dilution in direct-to-consumer drug advertisements

Direct-to-consumer (DTC) advertising of pharmaceutical drugs is often cited as the culprit for inflated patient demand for advertised drugs. Further to this economic concern, we provide an evidence-based psychological account of another concern that warrants the re-examination of the merits of DTC advertising of prescription drugs. Across six experiments and a sample of 3,059 US participants, we find reliable evidence for the argument dilution effect. Specifically, when commercials list severe side effects along with those that are most frequent (which include both serious and minor side effects), as required by the Food and Drug Administration, it dilutes consumers' judgements of the overall severity of the side effects, compared with when only the serious side effects are listed. Furthermore, consumers' reduced judgement of severity leads to greater attraction to those drugs. In regulating pharmaceutical advertisements, the Food and Drug Administration appear to have paradoxically dampened consumers' judgements of overall severity and risk, and increased the marketability of these drugs.