Increased promotion is associated with increased medicines sales, promotion influences prescribing more than doctors realise, and doctors rarely acknowledge that promotion has influenced their prescribing. Doctors who report relying more on promotion prescribe less appropriately, prescribe more often, and adopt new drugs more quickly.

Samples stimulate prescribing.

Doctors who receive drug company funds tend to request additions to hospital formularies. Drug company sponsorship influences the choice of topics for continuing medical education and the choice of research topics and the outcome of research. It leads to secrecy, delay in publication for commercial reasons, and conflict of interest problems for contributors to guidelines. Researchers often do not disclose funding from drug companies.

DTCA leads to increased requests from patients for medicines. Doctors who prescribe a requested drug are often ambivalent about the medicine.

Directions for future research

There are major gaps and weaknesses in the evidence. One important gap is the lack of evidence about public health outcomes of behaviour changes: does promotion lead to appropriate levels of use of medicines? The evidence that shows conclusively that doctors who rely more on promotion are poorer prescribers suggests that it does not. However, because these results could be due to other underlying doctor characteristics, this argument is somewhat weak. More work is needed to establish causal relationships between promotion and prescribing of drugs which have little or no place in rational prescribing, or which have serious adverse consequences when over-prescribed, such as antibiotics.

Other gaps include the lack of evidence from developing countries. All of the studies presented in this review are from developed countries. It is very difficult to untangle the effect of promotion from other inadequacies in systems of medicines distribution in developing countries. In addition there is less funding available for sophisticated studies. However the Cleary study¹²⁶ shows how a small, low budget project can provide quite convincing evidence.

Weaknesses include lack of clarity about what studies can and cannot prove. Some researchers do not seem appropriately sceptical about self-report data, and many infer causality from data which simply show associations. There is also some laxity in use of concepts, and in describing previous research. For example, in their survey Lurie et al.⁹⁸ asked about ‘changes in practice’ but in their discussion they discuss ‘changes in prescribing habits’. These are not equivalent. A change in practice could be one small change and may not be related to prescribing, while a change in habit suggests an ongoing and substantial change. Inaccurate descriptions of previous studies are sometimes found in literature reviews at the beginning of articles, particularly inaccurate claims about the conclusions that can be drawn from these studies. Future research needs greater methodological rigour in order to yield more definitive answers to the questions being posed.