- Concomitant medications are frequently used in the treatment of resistant psychiatric conditions to augment the primary psychotropic agent or to ameliorate side effects. The present study evaluated the prescription of concomitant psychiatric medications for psychiatric inpatients that were prescribed either olanzapine at its first commercial availability or another first-line antipsychotic agent. Sixty-nine newly admitted patients (mainly with schizophrenia) who were prescribed either olanzapine (n=35) or another first-line antipsychotic agent (n=34) were assessed (for the prescription of other concomitant psychotropic drugs) before (2–4 weeks prior to study) and following 8 weeks of treatment (unless discharged sooner). The results indicate that significantly fewer olanzapine-treated subjects were prescribed anticholinergic agents as compared to those prescribed other first-line antipsychotic agents, and a similar trend was noted in the prescription of mood stabilizers as well. Olanzapine-treated subjects used less as needed (PRN) antipsychotic medication compared to pre-olanzapine treatment period. Olanzapine-treated subjects used more anxiolytic agents compared to the control group in the early stages of treatment, probably due to the greater baseline severity of illness. These data suggest that olanzapine use is associated with less use of anticholinergic and mood-stabilizing agents as compared to older antipsychotic agents. These results also suggest that there is less need for PRN antipsychotic medication following olanzapine treatment. More severely ill subjects may require more anxiolytics during olanzapine initiation. The need for less anticholinergic and mood-stabilizing agent use with olanzapine could lead to greater adherence to long-term treatment and perhaps decreased cost (i.e. use of blood and organ system monitoring with mood stabilizers). At the end of treatment, olanzapine-treated subjects had statistically significantly lesser concomitant medicine usage compared to control subjects.