A Study of LY3541860 in Adult Participants With Relapsing Multiple Sclerosis

The main purpose of this study is to evaluate the safety and efficacy of LY3541860 in adult participants with multiple sclerosis that gets worse and gets better. The study will last about 9 months with additional 6 months follow-up.

Inclusion Criteria: * Participants must meet criteria for relapsing forms of multiple sclerosis, including relapsing-remitting multiple sclerosis based on the 2017 revision of the McDonald diagnostic criteria (Thompson et al. 2018) with a relapsing course (RMS) activity according to Klineova and Lublin 2018. * Participants must have 1 of these: * at least 1 documented relapse within the previous year * at least 2 documented relapses within the previous 2 years, or * at least 1 active GdE brain lesion on an MRI scan in the past 180 days prior to screening. * Have an Expanded Disability Status Scale (EDSS) score of less than or equal to (≤) 5.5 at screening and randomization. Exclusion Criteria: * Have had a diagnosis of: * primary progressive multiple sclerosis (MS) according to the 2017 revision of McDonald diagnostic criteria (Thompson et al. 2018), or * nonactive secondary progressive MS ( Klineova and Lublin 2018). * Meet criteria for neuromyelitis optica spectrum disorder (Wingerchuk and Lucchinetti 2022). * Have a history of clinically significant central nervous system (CNS) disease. * Have had a confirmed relapse with systemic corticosteroid administration \