Taylor and Bond used real prescribing data⁹⁴. They asked 201 doctors in Scotland to fill out duplicate prescriptions, which included details about perceived influences on prescribing. Of the 161 266 prescriptions most were either repeat prescriptions or drugs that the prescribers had prescribed in the past. New drugs formed a median of 3.5% of the prescription items per doctor. Sales representatives were mentioned as influences for 20% of new drugs added to doctors’ prescribing repertoires during the research period. Sales representatives were more likely to be listed as an influence on the prescribing of drugs used short-term. It is difficult to know how generalizable these findings might be. They may depend on the type of drugs that are being heavily marketed at the time, and other influences on prescribing at the time (Taylor and Bond note the concurrent introduction of a ‘limited list’).

Dasta et al.⁹⁵ also had objective evidence of prescribing. Their study, partly supported by Abbott Laboratories, looked at sources of doctors’ information about clarithromycin, a new antibiotic. The study was carried out in one inpatient and several outpatient medical care facilities. In the hospital, doctors who placed an order for clarithromycin were contacted by phone, and in the outpatient facilities doctors were sent a questionnaire when a prescription for clarithromycin, written by them, was presented at the pharmacy. In the hospital 65% of the doctors who prescribed clarithromycin reported not having had contact with a sales representative, and had never received or used samples of the drug at the time of the first interview. Eighteen per cent of outpatient prescribers had first heard about clarithromycin from a commercial source.

Peay and Peay⁹⁶ looked at the role of different information sources in specialists’ decisions to adopt new drugs. Each specialist was asked about his or her general drug adoption practices and also about one of eight target drugs. The results suggest that commercial sources of information are relatively unimportant to specialists, with only 4.7% of respondents naming any commercial source as the most influential in their decision to first prescribe the target drug.

These studies are better at identifying the influence of promotion than those that ask for a general self-assessment of the influence of promotion, because they isolate particular prescribing decisions. But they cannot be taken at face value because they rely on doctors’ own assessments of what has influenced their decisions.

Two studies, by Curry & Putnam⁹⁷ and Lurie et al.⁹⁸, relied entirely on self-assessments of reasons for prescribing changes. The former found that only 0.3% of their respondents (practicing doctors in Maritime Canada) reported changing their practice in the last year because of discussions with sales representatives. The latter surveyed faculty at seven university teaching hospitals in the USA and house staff in two of the teaching programmes, about their interactions with pharmaceutical representatives. Twenty-five per cent of the faculty and 32% of the residents reported that they had changed their practice at least once in the last year as a result of a discussion with a sales representative.

CONCLUSION: Doctors rarely acknowledge that promotion has influenced them to make specific prescribing changes. Specialists tend to report that promotion has less effect on them.