The primary objective of the study is to determine the effect of bismuth subsalicylate (Pepto-Bismol®) 524 mg versus placebo on gastrointestinal (GI)-related events reported in healthy volunteers receiving TECFIDERA™ (dimethyl fumarate [DMF]; also known as BG00012) twice daily (BID) The secondary objectives of this study in this study population are: To characterize the effect of bismuth subsalicylate (Pepto-Bismol®) 524 mg versus placebo on the frequency, severity, and duration of GI-related events and to evaluate GI-related events that lead to discontinuation of DMF.