Objective: To determine whether concurrent posttraumatic stress disorder (PTSD) should affect whether to augment or switch medications when major depressive disorder (MDD) has not responded to a prior antidepressant trial. Methods: Patients at 35 Veterans Health Administration medical centers from December 2012 to May 2015 with nonpsychotic MDD (N = 1,522) and a suboptimal response to adequate antidepressant treatment were randomly assigned to 3 “next step” treatments: switching to bupropion, augmenting the current antidepressant with bupropion, and augmenting with the antipsychotic aripiprazole. Blinded ratings with the 16-item Quick Inventory of Depressive Symptomatology-Clinician Rated (QIDS-C16) determined remission and response by 12 weeks and relapse after remission. Survival analyses compared treatment effects in patients with concurrent PTSD diagnosed with the Mini-International Neuropsychiatric Interview (n = 717, 47.1%) and those without PTSD (n = 805, 52.9%). Results: Patients diagnosed with PTSD showed more severe depressive symptoms at baseline and were less likely to achieve either remission or response by 12 weeks. Augmentation with aripiprazole was associated with greater likelihood of achieving response (68.4%) than switching to bupropion (57.7%) in patients with PTSD (relative risk [RR] = 1.26; 95% CI, 1.01-1.59) as well as in patients without PTSD (RR = 1.29; 95% CI, 1.05-1.97) (78.9% response with aripiprazole augmentation vs 66.9% with switching to bupropion). Treatment comparisons with the group receiving augmentation with bupropion were not significant. There was no significant interaction between treatment group and PTSD on remission (P=.70), response (P=.98), or relapse (P=.15). Conclusions: Although PTSD was associated with poorer overall outcomes, the presence of concurrent PTSD among Veterans in this trial did not affect the comparative effectiveness of medications on response, remission, or relapse after initial remission.