Neuroendocrine tests during treatment with neuroleptic drugs: I. Plasma prolactin response to chlorpromazine challenge.

Chlorpromazine (CPZ) 50 mg IM was administered to 21 schizophrenics receiving neuroleptic treatment. A further increase in plasma prolactin (PRL) was provoked in 8 subjects who had lower daily doses of neuroleptics than the remainder. The difference in the baseline PRL concentrations between the subgroups was inconsistent. In some patients, the test dose produced no change in plasma PRL but a further PRL rise was induced by raising the challenge dose or by an increase in the daily dose of neuroleptics. It is concluded that the PRL rise following CPZ 50 mg IM identifies some patients whose PRL response to the current treatment was only submaximal but the absence of PRL increment after this test dose is not sufficient evidence that the baseline level was already maximal.