Exposure and response prevention (EX/RP) can be delivered as monotherapy or to augment serotonin reuptake inhibitors (SRIs). While both options are considered effective OCD treatments, responses are heterogenous. Substantial work has investigated EX/RP predictors to account for this variability in responses, with mixed findings. Little research has studied whether EX/RP predictors may differ in medicated versus non-medicated samples (i.e., medication status as a moderator). We pooled data from two clinical trials conducted concurrently in the same specialty OCD clinic. One enrolled patients who were on stable SRI doses (EX/RP as SRI augmentation, n=58) while the other enrolled non-medicated patients (EX/RP monotherapy, n=38). Both trials used the same manualized EX/RP protocol and blinded independent evaluators. LASSO regression derived predictors and moderators of outcome. Improvement did not significantly differ between the EX/RP alone group and the SRI+EX/RP group. In both groups, higher baseline OCD severity and worse quality of life predicted poorer outcome. OCPD traits moderated results: Patients with more severe OCPD traits had better outcomes from EX/RP monotherapy than those receiving EX/RP with SRIs. Patient adherence to EX/RP homework mediated the associations between the baseline variables and outcome. The effect of OCPD traits on outcome warrants future study to improve care.