Secondary progressive multiple sclerosis (SPMS) is a phase of multiple sclerosis (MS) that may come after the relapsing-remitting phase. People in the relapsing-remitting phase of MS have recurring episodes (called relapses) of new or worsening neurologic symptoms. People who have SPMS tend to have fewer relapses, but their symptoms and disabilities slowly get worse over time. The shift between these 2 phases can be gradual and may even overlap. Because of this, some people have “active” SPMS, meaning they still have relapses in addition to slowly worsening disability. Current MS medicines, known as disease-modifying therapies (DMTs), are known to reduce the risk of relapses in people with relapsing-remitting MS, but the benefit of this treatment for people with SPMS is less clear. Recent studies have shown that some DMTs may help people with active SPMS. However, there have not been any previous studies comparing how effective different types of DMTs are for people with SPMS.