SS-31

SS-31 is one of the Szeto-Schiller (SS) peptides, a family of short synthetic peptides designed by Hazel Szeto and Peter Schiller. Their 2004 paper described cell-permeable peptide antioxidants built from alternating aromatic and basic amino acids, with dimethyltyrosine providing antioxidant activity; these peptides concentrated about 1,000-fold in the inner mitochondrial membrane ^[1].

SS-31 was later developed by Stealth BioTherapeutics under the name elamipretide. In September 2025 the FDA granted it accelerated approval, as Forzinity, to improve muscle strength in people with Barth syndrome weighing at least 30 kg ^[7]. It is also sold online as a research peptide under the name SS-31, which is not the approved product. It is sometimes discussed alongside MOTS-c, another peptide linked to mitochondria, though the two work differently.

Cardiolipin is a phospholipid found almost only in the inner mitochondrial membrane, where it shapes the folded cristae and helps organise the enzyme complexes that make ATP. A 2013 rat study showed that SS-31 binds cardiolipin with high affinity and blocks the peroxidase activity of the cytochrome c–cardiolipin complex, which otherwise damages cardiolipin under stress. Rats pretreated with SS-31 kept intact cristae during kidney ischaemia and recovered ATP more quickly ^[2].

A 2014 review by Szeto summarised this as a “cardiolipin-protective” mechanism: by binding cardiolipin, SS-31 stops cytochrome c acting as a damaging peroxidase while preserving its role in energy production. The review noted that the supporting evidence came largely from animal studies across many disease models ^[3].

In the original 2004 work, SS peptides reduced oxidative cell death in neuronal cells, prevented mitochondrial swelling in isolated mitochondria and improved contractile force in an isolated heart model of reperfusion injury ^[1]. Animal studies since then have covered kidney, heart, muscle and age-related conditions ^[3].

In people, the results have been mixed. In heart failure with reduced ejection fraction, a single four-hour intravenous infusion was safe in 36 patients and, at the highest dose, briefly reduced left ventricular volumes compared with placebo ^[4]. The largest trial, MMPOWER-3, randomised 218 adults with primary mitochondrial myopathy to daily elamipretide 40 mg or placebo for 24 weeks. It did not improve the six-minute walk test or fatigue scores, although the drug was well tolerated ^[5].

The approval is for Barth syndrome, an ultra-rare inherited disorder in which cardiolipin is abnormal. TAZPOWER began with a 28-week randomised, placebo-controlled phase followed by an open-label extension. Ten patients entered the extension and eight reached 168 weeks, with a cumulative improvement of 96.1 metres in six-minute walk distance from the start of the extension and improvements in some heart measurements ^[6]. The extension had no placebo group and very few patients. The US approval is an accelerated approval, a pathway under which continued approval can depend on further studies confirming clinical benefit.

MMPOWER-3 and the TAZPOWER extension used 40 mg by subcutaneous injection once daily ^{[5] [6]}. The heart failure study used single four-hour intravenous infusions of 0.005, 0.05 or 0.25 mg/kg per hour ^[4]. Animal studies used a range of weight-based doses that should not be converted to human doses. These are reported for information only; they are not a recommendation and do not apply to unregulated research material.

Across the published trials elamipretide was generally well tolerated. In MMPOWER-3 most adverse events were mild to moderate ^[5], and in the Barth syndrome extension the most common adverse events were injection-site reactions ^[6]. No serious adverse events occurred in the single-infusion heart failure study ^[4]. A 2026 review of peptides used in sports medicine, which included SS-31, cautioned that human safety data for peptides obtained outside the approved route are scarce ^[8].

Elamipretide (Forzinity) has US accelerated approval for Barth syndrome in patients weighing at least 30 kg, granted in September 2025, and was described as the first disease-specific treatment for the condition. It remains in development for other conditions, including dry age-related macular degeneration and mitochondrial myopathies ^[7]. We could not confirm an approval in the UK, EU, Canada, Australia or New Zealand as of September 2026.

SS-31 bought as a research chemical is not Forzinity and is not covered by that approval. Its legal position varies by country; see our legal status pages.

Research SS-31 is usually supplied as a freeze-dried powder, which is generally stored cold, dry and away from light, and refrigerated once reconstituted. See how to store peptides and bacteriostatic water.

PepFinder does not sell SS-31. You can compare prices, learn how to read a COA, and see which vendors publish third-party tested results.