Background: Because of the effect of the ever-growing evidence-based medicine movement on prescribing behaviour of doctors, the pharmaceutical industry incorporates bibliographical references to clinical trials that endorse their products in their advertisements. We aimed to assess whether the references about efficacy, safety, convenience, or cost of antihypertensive and lipid-lowering drugs included in advertisements supported the promotional claims.
Methods: We assessed all advertisements for antihypertensive and lipid-lowering drugs published in six Spanish medical journals in 1997 that had at least one bibliographical reference. Two pairs of investigators independently reviewed the advertisements to see whether the studies quoted to endorse the advertising messages supported the corresponding claims.
Findings: We identified 264 different advertisements for antihypertensive drugs and 23 different advertisements for lipid-lowering drugs. We recorded at least one reference in 31 advertisements in the antihypertensive group and at least one reference in every seven advertisements in the lipid-lowering group, providing a total of 125 promotional claims with references. We could not retrieve 23 (18%) references from monographic works and non-published data on file. 79 (63%) of the 125 references were from journals with a high impact factor; 84 (82%) of the 102 references retrieved were from randomised clinical trials. In 45 claims (44.1%; 95% CI 34.3-54.3) the promotional statement was not supported by the reference, most frequently because the slogan recommended the drug in a patient group other than that assessed in the study.
Interpretation: Doctors should be cautious in assessment of advertisements that claim a drug has greater efficacy, safety, or convenience, even though these claims are accompanied by bibliographical references to randomised clinical trials published in reputable medical journals and seem to be evidence-based.