OBJECTIVE: This study was designed to assess possible antidepressant effects of memantine, a selective N-methyl-D-aspartate (NMDA) receptor antagonist in humans. METHOD: In a double-blind, placebo-controlled study, 32 subjects with major depression were randomly assigned to receive memantine (5-20 mg/day) (N=16) or placebo (N=16) for 8 weeks. Primary efficacy was assessed by performance on the Montgomery-Asberg Depression Rating Scale (MADRS). RESULTS: The linear mixed models for total MADRS scores showed no treatment effect. CONCLUSIONS: In an 8-week trial, the low-to-moderate-affinity NMDA antagonist memantine in doses of 5-20 mg/day was not effective in the treatment of major depressive disorder.