Medications currently used to treat multiple sclerosis (MS) can merely reduce relapses during the initial relapsing-remitting phase. Many patients, however, develop progressive MS at a later stage, with disability becoming progressively worse. This type cannot be sufficiently treated at yet. Possible causes why an effective therapy for progressive MS is still lacking have been compiled by an international research team in a review article in the journal “Nature Reviews Drugs Discovery” from 9 August 2019.