This study analyses the efficiency of memantine–an antagonist of N-methyl-d-aspartate receptors–as adjunctive therapy for the treatment of negative symptoms of paranoid schizophrenia. Fifty-two patients (30 males; age 20–50 years) were included with the diagnosis of F20.014 and F20.024 according to the international classification of diseases (version 10). The patients had been receiving neuroleptic monotherapy with a fixed dose for a period of at least 4 weeks prior to randomization. Clinical data were collected 8 weeks after memantine had been introduced as part of the treatment regimen. A patient was considered as responding to treatment if they:

– scored 1-2 on the Clinical Global Impression Scale;

– showed a greater than 25% reduction of the total score on the Positive and Negative Syndrome Scale (PANSS) or a greater than 20% reduction on the negative subscale of PANSS.

Forty-seven patients were randomized: treatment group (neuroleptic + memantine, n = 24), control group (neuroleptic + placebo, n = 23); 44 patients completed the study. Neither memantine nor placebo led to a reliable decrease of negative symptoms, and the groups did not differ from each other. Future studies should pay more attention not only to the treatment of already formed negative and cognitive symptoms, but the prevention of their occurrence. Including through antagonists of N-methyl-d-aspartate receptors.