Adult outpatients with major depressive disorder and partial response or nonresponse to their current antidepressant ( as indicated by a @-item Hamilton Depression Rating Scale score of @ at baseline ) were randomized ( from July @-December @ ) to add memantine ( flexible dose @-@ mg/d , with all memantine group participants reaching the dose of @ mg/d ) ( n = @ ) or placebo ( n = @ ) to their existing treatment for @ weeks .