Adverse events and patients' perceptions of antihypertensive drug effectiveness.

Adverse events that patients attribute to their drug treatment are generally considered to reduce adherence to medication. However, some patients interpret such symptoms as indicating drug effectiveness. If perceivedly effective drugs are more likely to be taken then adverse events may increase adherence. The extent to which patients interpret adverse events as indicating drug effectiveness is not well known. We investigated this in a cross-sectional questionnaire study of 1013 drug-treated hypertensive patients from 55 primary health-care centres and 11 internal medicine clinics in Sweden. We hypothesized that estimates of future risk of complications of hypertension made by hypertensive patients who had adverse events would be lower than estimates made by patients who did not have adverse events, and that these estimates would only differ when patients were estimating their risks in a setting where they continued taking antihypertensive drugs. Patients' risk estimates were measured with visual analogue scales and adverse events were detected by an open question. Contrary to our hypothesis, patients with adverse events (25.7%) gave higher estimates of future risk in the continuing medication setting. This association persisted in a multivariate analysis, where a number of factors related to adverse events and risk were controlled for (OR 1.76 (95% CI, 1.26-2.45), P=0.001 for the most highly correlated risk measure), but risk estimates did not differ between patients with and without adverse events in the setting of not continuing medication. Possible explanations for these findings are pre-existing differences in attitude towards drugs and level of fear of complications.