Key Inclusion Criteria:  Have a diagnosis of MS and satisfy the approved therapeutic indication for DRF per the prescribing information. DRF prescribed and planned to be initiated within 60 days of enrollment or already initiated, with enrollment occurring no more than 7 days since the first dose.  Key Exclusion Criteria:  History of gastric bypass or required use of feeding tubes. Current enrollment in any interventional study or in any study which may conflict with this study, per the discretion of the principal investigator (PI) and Biogen Have received prior treatment with DRF (more than 7 days before enrollment).  NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.