Folate deficiency is associated with depression. Despite the biological plausibility of a causal link, the evidence that adding folate enhances antidepressant treatment is weak.
(1) Estimate the clinical effectiveness and cost-effectiveness of folic acid as adjunct to antidepressant medication (ADM). (2) Explore whether baseline folate and homocysteine predict response to treatment. (3) Investigate whether response to treatment depends on genetic polymorphisms related to folate metabolism.