If your antidepressant feels like it’s doing… nothing, there may be a missing piece. Some people carry variants of the MTHFR gene that make it harder to convert folic acid into the active form needed for the one-carbon cycle — a pathway required to produce serotonin and other neurotransmitters. If that pathway is sluggish, SSRIs like Lexapro, sertraline, or Prozac may not work as well. Clinical research shows that adding 15 mg of L-methylfolate, the bioactive form of folate, can significantly im