An open-label reversal drug study was undertaken on 10 neuroleptic-treated schizophrenic inpatients to assess the impact of amantadine hydrochloride on presumed prolactin-mediated neuroendocrine side effects. Measures were conducted across 7 weeks, including a 2-week neuroleptic baseline, a 3-week neuroleptic-plus-amantadine phase, and a 2-week return to the baseline regimen. Significant reduction with amantadine was observed on all six indices of neuroendocrine side effects: serum prolactin levels, body weight, gynecomastia/galactorrhea, breast tenderness, decreased libido, and amenorrhea. Improvement on these parameters was noted for as many as nine or all 10 patients, while in no cases was there worsening. In terms of motor and clinical effects, significant diminution of extrapyramidal and psycho-pathological symptoms was also achieved during this phase. The results suggested that amantadine may be beneficial for the treatment of neuro-endocrine side effects of antipsychotic medication owing to its ability to reverse neuroleptic-induced hyperprolactinemia.