Doctors’ own assessments of whether promotion affects their prescribing are of limited value in establishing whether this is the case. The research clearly shows that doctors who report relying more on commercial information, prescribe more heavily, less rationally, and adopt new medicines more quickly. Some researchers have interpreted this finding as showing that ‘relying on pharmaceutical company information increases prescribing’. This interpretation is not justified by evidence from these studies. The studies cannot show whether doctors would prescribe differently if their level of reliance on promotion were to change. Some doctors may have characteristics (such as attitudes, skills) that lead to both reliance on promotion, and heavy or irrational prescribing.

The studies that look at different levels of exposure to promotion (between prescribers or over time) and prescribing provide more convincing evidence that promotion changes behaviour. Further research using this kind of approach would be valuable. Simply replicating the Peay and Peay study in another place, using another drug, would strengthen the evidence considerably: similar findings would add substantial weight to the argument that contact with sales representatives does change prescribing behaviour. In addition, other studies that look at prescribing changes after exposure to promotion would be very useful. Cormack and Howells¹⁰⁵ and Strickland-Hodge and Jepson¹⁰⁸ used prescribing data from the Prescription Pricing Authority in the UK. Such data could be utilised further to observe prescribing changes, for example, before and after visits by sales representatives. Other countries where all or most prescriptions are subsidised by the government, such as Australia and New Zealand, have similar data available.

Samples appear to influence prescribing, but this has received little attention and needs further study. Other literature^122,124,125 has highlighted the widespread misuse of samples by health professionals, sales representatives and others, but ironically less is known about their use for patients.

Marketing literature tends to assume that evidence of behaviour changes is a good outcome: it shows investment in advertising is worthwhile. The public health and medical based literature tends to assume that higher prescribing levels of what is judged to be a sub-optimal medicine will lead to worse health outcomes. Some of the research suggesting that doctors who rely heavily on promotion prescribe differently does explicitly look at the quality of the prescribing (e.g., Haayer’s¹⁰⁴ use of an expert panel, or the extent of chloramphenicol prescribing in the study by Becker et al.¹⁰²). Such measures of appropriateness need to be used more.