Background and objective: Patients of community mental health services frequently self-report experiencing adverse drug reactions (ADRs). The objective of this study was to assess and discuss the pattern of psychiatric drug use observed among patients of a community mental health service in Sydney, Australia. Methods: This descriptive study was conducted from July 2005 to March 2006. Trained pharmacists conducted semi-structured interviews (30-45 minutes each) with 56 patients receiving psychiatric drugs and community-based case management for a long-term or persistent bipolar mood disorder or psychotic illness. The pharmacists reviewed drug charts, obtained community pharmacy dispensing records, and contacted other healthcare providers to compile a complete drug use record for each patient. These included prescription, non-prescription, and complementary and alternative medicines (CAMs). Patients' drug use records were analyzed using eight psychiatric drug use indicators: (i) high dose antipsychotics; (ii) antipsychotic polypharmacy; (iii) atypical polypharmacy; (iv) multiple 'when required' drugs; (v) sub-therapeutic doses of mood stabilizers; (vi) hypnotic prescribing; (vii) psychiatric therapeutic duplication (same therapeutic class); and (viii) ≥3 psychiatric drugs. Drug use records were also screened for 'potentially significant' drug-drug interactions using the Thomson Micromedex Drug-Reax® System. Results: The mean number of items (prescription drugs, non-prescription drugs, and CAMs) taken by each patient interviewed by the pharmacists was 7.80 ± 4.66. This included 2.91 ± 1.31 different psychiatric drugs by generic name, 0.86 ± 1.71 CAMs, and 1.00 ± 1.53 other non-prescription drugs. Twenty-eight patients (50%) were taking ≥2 psychiatric drugs from the same therapeutic class, and 23 (41%) were prescribed ≥2 antipsychotic drugs concurrently. Twenty-six patients (46%) were prescribed ≥1 antipsychotic drug at a dose exceeding that recommended in treatment guidelines. Potential drug-drug interactions were identified for 37 (66%) of the patients interviewed, with one or more potentially major drug-drug interactions being identified for 24 patients (43%). Conclusions: Psychiatric drugs were frequently used in combinations and doses outside those recommended in treatment guidelines. This highlights the importance of developing strategies to prevent and detect ADRs. Hence, regular and routine reviews of all drugs prescribed for patients of community mental health services may be warranted to minimize the risk of serious ADRs or drug-drug interactions.