Inclusion Criteria:  male or female age 18-55 years old DSM-5 diagnosis of OCD as primary presenting disorder CONTAM as the predominant symptom dimension (i.e., Dimension 4 (CONTAM symptoms) is the highest score on the Dimensional Yale-Brown Obsessive Compulsive Scale (D-YBOCS); participants with more than one Dimension as highest score will still be eligible as long as Dimension 4 is one of these) score of ≥ 8 on Dimension 4 of the D-YBOCS taking no psychiatric medications or on a stable dose of an SSRI or clomipramine for at least 8 weeks prior to enrollment. Use of PRN benzodiazepines will be permitted as long as the dose/usage has not changed significantly leading up to enrollment. No medication changes will be permitted during the study have not initiated a new course of exposure and response prevention (ERP) therapy within 8 weeks of enrollment (ongoing ERP will be permitted if initiated more than 8 weeks before enrollment).  Exclusion Criteria:  positive urine drug screen (other than prescribed benzodiazepines) use of psychiatric medications other than permitted above substance use disorder in the last 3 months (with the exception of nicotine) history of schizophrenia, bipolar disorder, autism, Tourette's syndrome (current and past history of depressive, anxiety, and eating disorders permitted as long as OCD is considered the primary disorder) active suicidal ideation over the week prior to screening (as indicated by answering yes to questions 1 or 2 on the C-SSRS) history of traumatic brain injury, seizure disorder, neurodegenerative disease, or other organic brain disease pregnancy or lactating contraindication to MRI scanning or TMS