It is well known that adherence to anti-depressant therapy is often poor, but the literature describes little in the way of systematic analyses to determine co-relation between treatment discontinuation and possible contributing factors. We used a community dispensing database to review anti-depressant prescribing patterns and continuity of therapy over a period of 10 months among a population of community-based general practice patients. Some 109,228 anti-depressant prescriptions were dispensed to 24,073 patients, of whom 37.5% collected a single prescription only. Tricyclic anti-depressant prescribing declined significantly during the observation period (from 70% of prescriptions in month 1 to 66% in month 10) while that of selective serotonin reuptake inhibitors (SSRIs) increased (23% in month 1, 28% in month 10) ( p < 0.0001). Some 27% of those on tricyclics were prescribed <50% of the defined daily dose (DDD) compared with 2% of those on SSRIs. Among patients new to therapy who collected >1 prescription, adherence was poor and declined over time. The factors that influenced the extent to which patients failed to adhere to therapy included dosage level (% DDD) and age ( p <0.0001 for both), but not drug class or sex. The findings suggest that low dosage is a contributory factor in treatment discontinuation, and that contrary to common perception, SSRIs are not necessarily associated with better adherence to therapy than tricyclics. Copyright (c) 2000 John Wiley & Sons, Ltd.