Low Field Magnetic Stimulation (LFMS) in Subjects With Treatment-Resistant Depression (TRD)

Inclusion Criteria: (Key) * Meets the Diagnostic and Statistical Manual of Mental Disorder, 5th Edition (DSM-5) criteria for Major Depressive Disorder (MDD), as determined by psychiatric evaluation. * Has TRD of the current MDE, as assessed at the site by the Massachusetts General Hospital/Antidepressant Treatment Response Questionnaire (MGH/ATRQ). * On an adequate dose of one antidepressant therapy (ADT) for at least eight weeks prior to the screening visit (Visit 1). The ADT dose must be stable for at least four weeks prior to the screening visit (Visit 1). Subjects must be willing to remain on the same stable dose of ADT upon signing the informed consent form until the end of the treatment observation period (end of Week 2) and, where possible, to the end of study participation Exclusion Criteria: (Key) * Have failed four or more lifetime adequate ADT treatment regimens (including the ongoing ADT for the current MDE). * Have been treated with adjunctive antipsychotic medication with an antidepressant for at least two weeks during the current depressive episode. * Are deemed to be at significant risk for suicidal behavior * Are unable to lie on their back for the duration of study treatment * Have a lifetime history of: 1. Delirium, dementia, amnestic, or other cognitive disorder; 2. Schizophrenia or any psychotic disorder, based on the Structured Clinical Interview for DSM-5 Axis I Disorders Patient Edition (SCID-I/P); 3. Bipolar I or II disorder, based on the SCID-I/P. * Have a current DSM-5 diagnosis at the screening visit (Visit 1) of: 1. An eating disorder active within the 12 months prior to the screening visit (Visit 1); 2. Comorbid anxiety disorders that predominate over MDD, as assessed by the investigator; 3. Alcohol or substance use disorder active within the 12 months prior to the screening visit (Visit 1); 4. Clinically significant DSM-5 Axis II disorder. * Have ever received electroconvulsive therapy, vagal nerve stimulation, deep brain stimulation or repetitive transcranial magnetic stimulation. * Have a non-removable programmable device or appliance such as cardiac pacemakers or cochlear implants. * Have any non-removable ferromagnetic implants, or conductive or other magnetic sensitive materials present in the head or neck . * Have a lifetime history of seizures or clinically significant electroencephalography abnormalities. A history of childhood febrile seizures is permitted.