This study evaluates an accelerated schedule of theta-burst stimulation using a Transcranial Magnetic Stimulation (TMS) device for treatment-resistant Obsessive Compulsive Disorder (OCD). In a randomized fashion, half the participants will receive accelerated theta-burst stimulation at the dorsomedial prefrontal cortex (DMPFC), while half will receive accelerated theta-burst stimulation at the right orbitofrontal (rOFC) site.

Medications (SSRIs and D2 antagonists) and cognitive-behavioral therapy are the mainstays of treating OCD; however, many patients show only a partial response, and more than 25% of patients show no improvement with these treatments. Repetitive transcranial magnetic stimulation (rTMS) is a promising alternative, using powerful, focused magnetic field pulses to stimulate target brain areas. So far, at least two stimulation targets have consistent evidence of efficacy in OCD: the dorsomedial prefrontal cortex (DMPFC) and the orbitofrontal cortex (OFC). Patients often show a strong response to one target but not the other. It is not well understood why some patients respond, while others do not.

The investigators previously developed methods for discovering neurophysiological subtypes of depression based on resting state functional Magnetic Resonance Imaging (fMRI) measures of functional connectivity (RSFC) in relevant brain networks; diagnosing them in individual patients; and using them to predict individual differences in rTMS response. Subsequently, motivated by recent studies characterizing individual variability in the topology of these functional networks, the investigators have optimized methods for improving the accuracy of these predictions by accounting for individual variability, stabilizing the selection of treatment-predictive features, and increasing robustness in replication samples through regularization. Here, the investigators propose applying these methods to discover novel network-based subtypes of OCD and develop prognostic neuroimaging biomarkers for predicting differential treatment response to rTMS targeting the DMPFC or OFC, which could subsequently be tested in a randomized clinical trial.

Inclusion Criteria:

1. meets Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) criteria for OCD with a moderate level of severity as defined by a Yale-Brown Obsessive Compulsive Scale (YBOCS) score of at least 18.
2. stable on Serotonin Re-uptake Inhibitor (SRI) medication for at least 8 weeks prior to (with plans to continue throughout) the study Note: Medications that are known to increase cortical excitability (e.g., buprorion, maprotiline, tricyclic antidepressants, classical antipsychotics) or to have an inhibitory effect on brain excitability (e.g., anti-convulsants, benzodiazepines, and atypical antipsychotics), or any other medications with relative hazard for use in TMS will be allowed upon review of medications and/or motor threshold determination by TMS specialist.
3. failed at least 1 prior trial of standard first-line OCD treatment per American Psychological Association (APA) Practice Guidelines (serotonin reuptake inhibitor [SRI] or cognitive behavioral therapy with exposure and response prevention)OR had refused these treatments for individual reasons.
4. capacity to provide informed consent.
5. ability to tolerate clinical study procedures.
6. successfully complete the screening forms at the Stanford Center for Cognitive and Neurobiological Imaging (CNI) without any contraindications.

Exclusion Criteria:

1. Current psychosis (re-assessed only if screening appointment was more than 30 days ago - Structured Clinical Interview for DSM-IV (SCID) - 5 Module B)
2. Current bipolar disorder (assessed during baseline if screening appointment was more than 30 days ago - SCID-5 Module D)
3. Severe depression [Note: 17-item Hamilton Depression Rating Scale (HDRS-17) must be less or equal to 20 to enter study, assessed during baseline if last assessment was more than 1 week ago]
4. Current active suicidality (as determined by C-SSRS at baseline of 3 or above)
5. Current moderate or severe Alcohol Usage Disorder or Substance Usage Disorder (except nicotine and caffeine) according to the DSM-5 criteria (assessed only if screening appointment was more than 12 months ago - SCID-5 Module E)
6. Current eating disorder (assessed during baseline if screening appointment was more than 3 months ago - SCID-5 Module I)
7. History of seizure, having an EEG, stroke, head injury (including neurosurgery), implanted devices, frequent or severe headaches, brain related conditions (e.g., intracranial mass lesions globe injuries, hydrocephalus), illness that caused brain injury or first degree relative with seizure disorder (assessed during screening via medical history assessment and TMS Safety Screen by study MD)
8. Individuals with primary hoarding disorder without a DSM-5 OCD diagnosis (as determined by SCID-5 and YBOCS checklist assessed only if screening appointment was more than 30 days ago)
9. Planning to commence Cognitive Behavioral Therapy (that includes exposure and response prevention) during the period of the study or have begun Cognitive Behavioral Therapy within 8 weeks prior to enrollment (assessed during baseline by study MD)
10. Pregnant or nursing females (assessed via urine dipstick if screening appointment was more than 30 days ago)
11. Positive urine screen for illicit drugs (assessed via urine dipstick if screening appointment was more than 30 days ago) [Exceptions: (1) any prescribed medication that participant is currently taking and (2) positive cocaine metabolite after consumption of coca tea]
12. History of any implanted device or psychosurgery (assessed during baseline by study MD)
13. History of receiving Electroconvulsive Therapy (ECT) (assessed during baseline by study MD)
14. Age of OCD symptom onset >30