MS-SMART will test the efficacy and mechanism of action of three repurposed drugs (fluoxetine, riluzole and amiloride). All three drugs are in human use and have a good safety record. Critically for the purpose of MS-SMART they all have shown promise in early phase human MS clinical trials and target one or more of the pivotal neurodegenerative causing pathways implicated in SPMS. This is a Type B trial, as the IMPs are all in human use, have a good safety profile but are not currently used for this patient population.