Medications are central to the psychiatric armamentarium in United States jails and prisons. Psychiatric medications are used both to stabilize acute symptoms as well as maintain mental health once symptoms are reduced. Both jails and prisons rely heavily on traditional antipsychotics, but both have a full array of atypical medications in their formularies (reference book of pharmaceutical products). In terms of formulary decisionmaking, both jails and prisons are influenced most by personal clinical experience, research-demonstrated effectiveness, FDA approved indications, and exposure through continuing education or professional meetings. Cost is not among the most important factors, but also is not among the least important. It appears that psychiatric staff in jails and prisons must balance good clinical practice with costs. The heavy reliance on cheaper medications, when alternatives are present, suggests that cost remains a factor. The fact that psychiatrists prescribe off the formulary and are more influenced by demonstrated effectiveness, in contrast, supports the notion that they are indeed concerned with good practice. Additional research is warranted to explore the complex pressures facing psychiatric staff in providing the best services in a very difficult environment. Tables, references