To the Editor: One concern that medical practitioners and pharmacists have about patient counselling is the uncertainty about the amount of information which should be given to patients, especially regarding possible adverse reactions to medications.1 Studies have found that providing information on possible adverse reactions can affect patients' willingness to take the medication.1

Research in cognitive psychology provides clear evidence that the order in which information is presented has a significant influence on judgement. Information received first is likely to have a disproportionately large effect on judgement, the "primacy effect".2-4 Despite clear evidence supporting the "order effect" in diverse areas, research has not been undertaken to investigate whether the order effect is present in medication information.

To test the hypothesis that differently ordered sequences of the same information about a drug can result in different judgements,5 804 subjects were presented with a short description of a fictitious medication. The descriptions were presented in one of two formats (Box): (A) positive–negative (therapeutic benefits followed by potential adverse reactions) or (B) negative–positive order (potential adverse reactions followed by therapeutic benefits). The surveys were randomly distributed to university students, mindful of the limitation of extrapolating the data to the general population. Subjects rated the medication (from very bad to very good) and the likelihood of taking the medication (from very unlikely to very likely) on seven-point Likert scales. For analysis, we used the independent sample t test, which is robust and therefore considered suitable for this analysis.

Of the 804 completed questionnaires, 403 were in the positive–negative order and 401 were in the negative–positive order. Participants given the positive–negative description of the medication rated it more positively (mean, 4.43; SD, 1.02) than those given the negative–positive description (mean, 3.70; SD, 1.62) (P < 0.001). Similarly, participants reported a higher likelihood of taking the medication when information was presented in the positive–negative order (mean, 4.23; SD, 1.62) compared with the negative–positive order (mean, 3.54; SD, 1.66) (P < 0.001).

We found that the order of presentation of medication information significantly affected judgement of the medication. Subjects rated the medication more favourably when positive information was presented first. These results suggest a potential benefit in presenting medication benefits before discussion of possible adverse effects. Such an approach might apply to medical practitioners and other healthcare professionals when counselling patients. It might also be a consideration in the format of written information, such as Consumer Medicine Information.