MITIGATEA Multicenter, Double- Blind, Placebo- Controlled Study of Montelukast on Gastrointestinal Tolerability in Patients With Relapsing Forms of Multiple Sclerosis Receiving Tecfidera® (Dimethyl Fumarate) Delayed Release Capsules

Study start date: March 12, 2015

Key Inclusion Criteria: * Reside in the United States and have a confirmed diagnosis of a relapsing form of MS and satisfy the therapeutic indication as described in the local label * As perceived by the Investigator, have the ability to comply with all requirements of the study protocol and to operate the eDiary required to record GI-related events * Female participants of childbearing potential who are not surgically sterile must practice effective contraception during their participation in the study and be willing and able to continue contraception for 30 days after they complete or withdraw from the study. All men must practice effective contraception, and they should not donate sperm throughout the study and for at least 90 days after their last dose of study treatment. Key Exclusion Criteria: * History of significant GI disease (for example, irritable bowel disease, peptic ulcer disease, history of major GI surgery, eosinophilic GI disease, or food allergies) * Chronic use (≥7 consecutive days) of bismuth subsalicylate, simethicone, calcium carbonate, loperamide, proton-pump inhibitors, or ondansetron within 1 month prior to the Screening Visit * Use of the following medications: montelukast, immunotherapy, mast cell stabilizers, or parenteral, inhaled, or oral steroids up to 1 month prior to the Screening Visit. Use of these medications is also not permitted for the duration of the study (except for the use of montelukast as per study protocol) and will lead to discontinuation * Have one or more major comorbidities that, in the opinion of the Investigator, may affect the outcome of the study * History of malignancy (except for basal cell carcinoma that had been completely excised prior to study entry), severe allergic or anaphylactic reactions or known drug hypersensitivity, abnormal laboratory results indicative of any significant disease, and/or a major disease that would preclude participation in a clinical study NOTE: Other protocol defined Inclusion/Exclusion criteria may apply