This is a multi-center, randomized, double-blind, placebo-controlled study to demonstrate the safety, tolerability, and effect of ACTH on fatigue in patients with relapsing multiple sclerosis (RMS). The primary objective of this study is to assess the efficacy of ACTH versus placebo in reducing fatigability in patients with RMS. Secondary objectives include assessment of the tolerability and safety of twice-weekly ACTH treatment vs. placebo and evaluation of ACTH on depression, sleepiness, and quality of life measures and correlations between these measures.