OBJECTIVE: To observe patterns of antidepressant use and concomitant psychotropics as an index of clinical prescribing practice. METHODS: Among 1.6 million members of Merck-Medco followed continuously between 1/1/96-12/31/98, we identified all patients (N=42,510) who received a new antidepressant prescription (defined as none within the prior 12 months) in 1997 (Index AD). We observed the time between the use of other concomitant psychotherapeutics (e.g. conventional antipsychotics(AP)/ atypical antipsychotics(AP-A), benzodiazepine, anxiolytics(ANX)/buspirone(ANX-B), sedative/hypnotics(SH) and zolipidem(SH-Z)) in the year prior to or year after the index AD prescription. RESULTS: 14, 792 (34.8%) AD patients were prescribed a concomitant psychotherapeutic agent. All classes of concomitant psychotherapeutics revealed a similar general pattern: a steady increase in daily use in the year prior to an index AD, a peak on the index AD date, and a tapering over the next year. However, patients were more likely to receive a conventional antipsychotic and anxiolytic prior to the index AD, and an atypical antipsychotic and buspirone after the index AD. Concomitant % of AD patients Pre-Index AD(cumulative-1yr) Same Day Post-Index AD(cumulative 1yr) AP 2.28 .87 30 1.12 AP-A 2.36 .58 .38 1.40 ANX 21.30 12.30 1.99 7.00 ANX-B 3.73 1.58 .36 1.79 SH 5.73 2.98 .37 2.37 SH-Z 8.96 4.25 .75 3.97 CONCLUSIONS: Whereas we hypothesized excessive benzodiazepine and hypnotic usage pre- and post-index AD, we noted lower than expected usage. We did not expect the pattern of increased atypical antipsychotic usage on the same day or subsequent to an index AD. We speculate that continuing medical education of physicians may be contributing to a decrease in the putative misuse of benzodiazepines and hypnotics.