Effect of clozapine and adjunctive high-dose glycine in treatment-resistant schizophrenia

Objective: The focus of this study was the systematic evaluation of the cli nical effects of glycine as an adjunct to the atypical antipsychotic clozap ine in the treatment of schizophrenia. Method: In a double-blind, placebo-c ontrolled study, 19 patients with chronic, treatment-resistant schizophreni a who were maintained on optimal doses of clozapine (400-1200 mg/day) were administered either 30 g/day of glycine (N=9) or placebo (N=10) for 12 week s. Clinical evaluations with the Brief Psychiatric Rating Scale, the Scale for the Assessment of Negative Symptoms, and the Simpson-Angus movement sca le were completed biweekly. Results: The use of glycine as an adjunct to cl ozapine was not effective in decreasing positive or negative symptoms. In c ontrast, the patients treated with clozapine without glycine had a 35% redu ction in positive symptoms. Conclusions: These preliminary data suggest tha t glycine may interfere with the antipsychotic efficacy of atypical neurole ptics such as clozapine.