Pharmaceutical company executives must believe that advertising is effective. Otherwise, pharmaceutical advertising would be illegal under the Australian Corporations Act 2001 (Cwlth), which requires that company staff rationally believe their business judgements to be in the best interests of their corporation.1 However, Henderson and colleagues’ study in this issue of the Journal may have found an advertising delivery channel that does not work (→ The effect of advertising in clinical software on general practitioners' prescribing behaviour).2 They compared prescribing by general practitioners exposed to advertisements in clinical software with prescribing by unexposed GPs during 2003–2005. Despite a large sample size and carefully controlling for many possible confounders, they did not detect any significant difference in prescribing for six of the seven drugs studied. Interestingly, there was significantly less prescribing of one drug by exposed GPs — possibly a false-positive finding arising by chance, but this is the first ever published evidence that pharmaceutical advertising may sometimes unintentionally reduce sales.