There is little literature on the effect of samples on prescribing. Backer et al.¹²¹ report an ethnographic study of 18 medical practices. At least four weeks of fieldwork were done in each practice. Samples were used in 19.8% of the 1588 patient encounters observed. This varied widely between practices (range 4% to 39%) and also between doctors within each practice. Reasons given for using samples included, to test for efficacy and tolerability, to offer temporary relief or convenience, and/or to reduce costs to patients.

In Morelli and Koenigsberg’s study¹²² samples which were dispensed as new medication for chronic problems were accompanied by a prescription for the same brand 48% of the time. This finding is hard to interpret, but it may suggest that the availability of a sample influences the choice of brand prescribed. This
area needs further investigation.

Chew et al.¹²³ used three hypothetical case studies and asked their respondents (131 general medicine and family physicians) which medicine they would prescribe. They were then given a list of samples available and asked whether they would prescribe their drug of choice, or give a sample of another drug. For a patient with hypertension (and no health insurance) almost all respondents (92%) ideally chose a diuretic or beta-blocker (consistent with practice guidelines). However when samples were available, 27% (35 doctors) said they would dispense a sample. In almost all of these cases the sample was a different class of drug (e.g. ACE inhibitor or calcium channel blocker). Almost all of those who would give a sample (97%) said avoiding cost to the patient was an important or very important reason for their choice. A follow-up scenario in which the patient returns, with their hypertension well controlled on the sample drug, and now with health insurance, was presented. Of the 35 doctors who had said they would dispense a sample, 24 would now write a prescription for the sample drug, to avoid switching the patient. If this reflects real behaviour, it suggests that in some circumstances drug samples may strongly influence prescribing.

CONCLUSION: Samples appear to influence prescribing but more research is required on this issue.