Twenty (n=20) Veterans between the ages of 18-55 years with MDD will be recruited for participation in an open-label trial of creatine augmentation. Veterans with depression will have unremitted MDD, despite having had an adequate trial of an SSRI antidepressant. Participants with MDD will be treated with oral creatine 5 gm daily for 8 weeks and will continue taking their SSRI antidepressant. Participants will undergo brain scanning at baseline, and the scans will be repeated following 8 of adjunctive creatine.