Double-blind, placebo-controlled, crossover trial of glycine adjuvant therapy for treatment-resistant schizophrenia

Background. It has been proposed that schizophrenia is associated with underactivity of brain glutamatergic neurotransmission, especially at the level of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor. Glycine potentiates NMDA receptor-mediated neurotransmission, indicating that it may serve as an effective therapeutic agent in the treatment of schizophrenia. Method. Eleven treatment-resistant patients with chronic schizophrenia completed a double-blind, placebo-controlled, six-week, randomly assigned, crossover treatment trial of 0.8 g/kg body weight/day of glycine, added to their prior antipsychotic treatment. Results. Glycine was well tolerated, resulted in significantly increased serum glycine levels and induced a mean 36 (7%) reduction in negative symptoms (P <0.0001). Significant improvments were also induced in depressive and cognitive symptoms. The greatest reduction in negative symptoms was registered in the patients who had the lowest baseline serum glycine levels. Conclusions. These results extend previous findings and suggest an additional approach to the pharmacotherapy of negative symptoms and cognitive deficits in schizophrenia.