MS-SMART is a multicentre, multi-arm, double blind, placebo-controlled phase IIb randomised controlled trial. A total of 440 patients with SPMS, with an entry criteria of an EDSS score of 4.0-6.5 will be equally randomised to receive placebo or one of the three active agents (fluoxetine 20mg bd, amiloride 5mg bd or riluzole 50mg bd). Patients will be followed up for 96 weeks with outcome-data collected after 0, 24, 48 and 96 weeks. That is, the duration of the trial for a trial participant is 96 weeks (a telephone assessment at week 100, 4 weeks post completion will be conducted). This is standard practice for phase II trials in SPMS.