Seven patients with recurrent refractory psychotic depressive illness were treated with tricyclic antidepressants plus methylphenidate (Ritalin). The effect of methylphenidate appears to involve an increase in the blood levels of antidepressants through enzymatic inhibition of the metabolism of imipramine and desmethylimipramine that is concomitant with clinical improvement. The potentiation by methylphenidate may have important implications for the treatment of depression.Abstract Teaser