What it is: The synthetic form of folate, a B vitamin (B9) found in fruits, leafy vegetables, and other foods, that affects the neurotransmitters known as monoamines. Folic acid is sold in stores as a capsule or tablet.
The evidence: Folate deficiency is common among depressed people, especially those who dont respond to antidepressants. Folic acid has never been tested as a stand-alone treatment for depression, but it has been compared with placebo as an addition to Prozac. In one study, patients who received folic acid responded better than those who received placebobut only the female patients. Nearly 95% of the women who received folic acid responded to the combo treatment, compared to about 60% of the women who received the placebo.
Other forms of folate that are more chemically complex have been tested on their own. In one early ‘90s study involving elderly depressed patients, a type of folate known as 5-methyltetrahydrofolate (5-MTHF) was found to be roughly as effective as the antidepressant trazodone.
The bottom line: The evidence for the use of folic acid in depression is limited and inconclusive. (The Natural Standard Research Collaboration, an independent research group, has given the evidence a “C” grade.) 5-MTHF and a related form of folate called L-methylfolatewhich is available as the “prescription medical food” Deplinmay be helpful as an addition to antidepressants, but you should be wary of nonprescription products that list 5-MTHF, L-methylfolate, or “optimized folate” as the main ingredient.