In this small outpatient pilot study, allopurinol augmentation did not show a statistically significant improvement over placebo in attenuating manic symptoms. Subjects with restricted caffeine use showed a greater effect size compared to caffeine users. This finding may be interpreted as corroborating the hypothesized mechanism of action of allopurinol's anti-manic effect in previous studies.

Several studies have demonstrated that psychomotor retardation is an important sign of the major depressive episode, both from a diagnostic point of view and as a predictor of treatment outcome. However, it is uncertain to what extent psychomotor retardation is specific for the major depressive episode. A heterogeneous group of psychiatric patients (n=26) was studied using a rating scale developed specifically to assess psychomotor retardation (RRS). The 13 patients suffering from a major depressive episode had a significantly higher RRS score than patients with another diagnosis. Furthermore, in the depressive subjects the severity of the depression (measured by means of Hamilton's depression rating scale) appeared to correlate with the severity of the psychomotor retardation. Cognitive features of psychomotor retardation were mainly responsible for the more severe psychomotor retardation in the depressive patients. Surprisingly. Hamilton's depression scale which was used in this study does not pay much attention to these aspects.