Following informed consent and verification of entry criteria by the core units, study participants will be randomized 1:1 to either Tecfidera (120mg by mouth twice daily for 7 days with dose escalation to 240mg by mouth twice daily) or placebo. Clinical follow-up by the treating physician will occur at weeks 0, 48, and 96. During clinical visits, comprehensive medical history data will be obtained by the treating physician. Clinical examinations as defined within this protocol will be performed at weeks 0, 48, and 96 and during or immediately following clinical exacerbations. All reported acute or progressive clinical events will be adjudicated by the Central Clinical Unit. Clinical visits due to suspected exacerbations associated with CNS (central nervous system) demyelination, and associated diagnostic studies and treatments, will be covered under the medical standard of care by third party payers. A recommendation to re-evaluate the patient within 3 months following the clinical event to assess for extent of recovery will be made. In addition to the face-to-face visits described above, study participants will be contacted over the telephone at weeks 4, 8, 36, 60, and 84 to assess for medical or treatment difficulties and for study medication compliance. Standardized MRI studies of the brain will be performed at weeks 0 and 96. Clinical imaging studies of the brain and/or spinal cord performed during or immediately following the onset of a clinical exacerbation will be performed at the discretion of the site PI with scan costs covered under the medical standard of care. An end of study clinical MRI of the cervical spinal cord with and without contrast will be recommended to study participants at week 96 as medical standard of care.