In the present study, olanzapine was administered to 20 hospitalized schizo
phrenic patients with an acute episode of relapsing disease, following an o
pen baseline controlled design. In addition to assessment of efficacy and s
afety, the effects of treatment on plasma levels of amino acids, 5-HT param
eters and norharman were evaluated. Olanzapine induced antipsychotic effect
s without inducing any EPS and was associated with significant weight gain
in a majority of patients. In half of the nonresponders, a subjective impro
vement of well being and general functioning was observed that could not be
related to reduction of psychopathological features. Nonresponders appeare
d to present with clinically more severe arousal-like symptoms as assessed
with a subset of PANSS items. Non-response to treatment with olanzapine was
found to be associated with lower 5-HT plasma concentrations at baseline a
nd enhanced 5-HIAA plasma levels during the experimental period.