To assess the effect of pharmaceutical advertising embedded in clinical software on the prescribing behaviour of general practitioners.

Secondary analysis of data from a random sample of 1336 Australian GPs who participated in Bettering the Evaluation and Care of Health, a national continuous cross-sectional survey of general practice activity, between November 2003 and March 2005. The prescribing behaviour of participants who used the advertising software was compared with that of participants who did not, for seven pharmaceutical products advertised continually throughout the study period.

Prescription for advertised product as a proportion (%) of prescriptions for all pharmaceutical products in the same generic class or group.

GP age, practice location, accreditation status, patient bulk-billing status and hours worked were significantly associated (P < 0.05) with use of advertising software. We found no significant differences, either before or after adjustment for these confounders, in the prescribing rate of Lipitor (adjusted odds ratio [AOR], 0.90; P = 0.26); Micardis (AOR, 0.98; P = 0.91); Mobic (AOR, 1.02; P = 0.89); Norvasc (AOR, 1.02; P = 0.91); Natrilix (AOR, 0.80; P = 0.32); or Zanidip (AOR, 0.88; P = 0.47). GPs using advertising software prescribed Nexium significantly less often than those not using advertising software (AOR, 0.78; P = 0.02). When all advertised products were combined and compared with products that were not advertised, no difference in the overall prescribing behaviour was demonstrated (AOR, 0.96; P = 0.42).

Exposure to advertisements in clinical software has little influence on the prescribing behaviour of GPs.