Background: Being overweight or obese may be associated with poor response to antidepressants. The present report explores the moderation of antidepressant response by body weight to establish the specificity to antidepressant mode of action, type of depressive symptoms and gender. Methods: Height and weight were measured in 797 men and women with major depression treated with escitalopram or nortriptyline for twelve weeks as part of the Genome Based Therapeutic Drugs for Depression (GENDEP) project. Body mass index (BMI) and obesity (BMI > 30) were tested as predictors of change in depressive symptoms using mixed linear models. Results: Higher BMI and obesity predicted poor response to nortriptyline but did not significantly influence response to escitalopram. The moderation of response by body weight was due to differential improvement in neurovegetative symptoms, including sleep and appetite. The relationship between body weight and change in neurovegetative symptoms was moderated by gender with obese men responding less to nortriptyline and obese women having poorer response to both antidepressants. Limitations: As no placebo arm was included, the specificity of findings to antidepressants is relative. Lack of specific measures precluded accounting for differences in body fat distribution. Conclusions: Body weight should be considered in the assessment of depression as it may inform the selection of antidepressant treatment. © 2009 Elsevier B.V. All rights reserved. ; SCOPUS: ar.j ; info:eu-repo/semantics/published