At the beginning of the second phase, participants will be randomly assigned to receive either NIM or a placebo in addition to continuing with the antidepressant medication already helping them. Participants will take NIM or the placebo for 8 months, undergoing weekly study visits for the first month and monthly study visits for the last 7 months. During these visits, researchers will monitor the participants' health and reactions to their medications. After 4, 16, and 32 weeks, an EKG test will be performed, and after 16 and 32 weeks, cognitive and physical tests will be performed again. After the 8 months, participants will attend three weekly study visits while their use of medication is lowered and then ended.