SS-31 (elamipretide, also MTP-131) is a synthetic aromatic-cationic tetrapeptide, D-Arg-Dmt-Lys-Phe-NH2, in which Dmt is 2',6'-dimethyltyrosine. It belongs to the Szeto-Schiller (SS) peptides, a series designed to be cell-permeable and to target the inner mitochondrial membrane. It has been studied in isolated mitochondria, cell culture and rodent models of ischaemia-reperfusion injury and ageing, and has been the subject of registered clinical trials, including a phase 3 trial in primary mitochondrial myopathy. A 2025 review summarises its structure, proposed mechanism and development programme.