Our data indicate that a cross-sectional relationship exists between number of prescription drugs used and "responsiveness" to DTC advertising. This strong linear relationship remains even when controlling for demographic and socioeconomic variables and self-reported health. Overall, 25.3% of respondents were motivated by DTC advertising to initiate discussion regarding new health problems. Among respondents taking no prescription medications, fewer than 10% were motivated by DTC advertising. Conversely, among respondents taking five or more prescription medicines, nearly 40% were motivated.
In 2002, the Government Accountability Office has identified 13 surveys, primarily for lay publications, which attempted to assess consumer behavior related DTC advertising. Since that time several additional surveys have been published in the medical and scientific literature[10, 14–16]. In these studies, the proportion of respondents who reported being influenced by DTC advertising to seek medical care ranged from 10.5 to 35%. Although there is some variation in how each survey defines responsiveness to DTC advertising, our finding that 25% of respondents had discussed a new medical condition with a physician based on DTC advertising is generally consistent with others.
Our results confirm those of previous studies, [10, 17] which identify older age, lower educational attainment and a positive attitude towards DTC advertising as factors associated with responsiveness to DTC advertising[9, 10]. In contrast to other studies, [14, 18] we did not find an association between ethnicity, income or self-reported health status and DTCA.
We found that a cross-sectional relationship exists between responsiveness to DTC and self-reported use of prescription, but not OTC, drugs. Because there was a trend towards poorer self-reported health and responsiveness to DTC, is plausible that users of prescription medications represent a sicker population, and one that may be more attuned to the messages conveyed in DTC advertising. Alternatively, because DTC advertising largely focuses on prescription medications, persons who are responsive to DTC may have approached their prescribers based on information in DTC, resulting in more prescription, rather than OTC, use. Bell and colleagues found that current users of prescription drugs were more likely to be influenced by DTC advertising, but did not quantify the number of prescriptions, and limited their sample to one county in California.
Our investigation confirms results of a smaller study of Minnesotans by Schommer et al.  that found prescription medication use to be statistically greater in respondents who were responsive to DTC advertising than those who were not. Similar to our results, no significant difference was found in the number of OTC medications used by responsive versus unresponsive patients.
The main strength of our study is that the source of data comes from a large nationally representative sample with a high response rate. Furthermore, unlike some other studies, OTC as well as prescription drug use was ascertained. Our study has several limitations. First, these data were collected in 1999. Penetration and awareness of DTC advertising, as well as types of media outlets (e.g. internet), have increased considerably in subsequent years. Despite this, however, we are encouraged by similarities in regard to attitudinal, socioeconomic and demographic predictors of susceptibility to DTC advertising demonstrated in more recent surveys, [14, 15] and likewise feel that the relationship between number of prescription drugs used and susceptibility to DTC advertising should be no less true today. Second, this is a secondary analysis of FDA data originally collected to investigate attitudinal and demographic effects toward DTC advertising; thus, rigorous ascertainment of medication use was not included. Although the self-reported medication use measure is a limitation, it has been used in a previous survey of DTC advertising, and has been found to be congruent with pharmacy prescription data[19, 20].
The cross-sectional nature of this study does not allow for unequivocal statements regarding the direction of causality. Although this relationship could be explained by physician compliance with patient requests for medications, it is also plausible that DTC advertisements have a particular appeal to patients prone to taking multiple medications. Finally, the main measure in this study specifically asks about initiating discussion with a physician about a new medical problem and thus may not have captured those patients who use DTC advertisements to prompt discussion of previously discussed problems, or those patients who may have discontinued a medication due to information contained in DTC advertisements.