The role of L-methylfolate in depressive disorders.

Major depressive disorder (MDD) is a debilitating and often recurrent illness. An initial antidepressant trial is effective at achieving remission for approximately 30% of patients when prescribed as monotherapy, with the majority of patients returning as partial or non-responders. Switching antidepressants or adding augmentation agents are standard therapeutic options used to achieve and maintain remission. Suboptimal serum and red blood cell folate levels have been associated with a poorer response to antidepressant therapy, a greater severity of symptoms, later onset of clinical improvement, and overall treatment resistance. This Expert Review Supplement reviews the evidence for L-methylfolate as an augmentation agent in depression and discusses its clinical use elaborated by three clinical presentations.