Educational reference, not medical advice. This page summarizes information from published research and regulatory filings for educational purposes. It is not a recommendation to use any compound and should not replace guidance from a licensed healthcare provider. Most peptides discussed here are not approved for the uses described.
What it is
SS-31 — the research designation for elamipretide, also known as Bendavia and MTP-131 — is a synthetic aromatic-cationic tetrapeptide (D-Arg-2,6-dimethyl-Tyr-Lys-Phe-NH2) that crosses cell membranes and concentrates on the inner mitochondrial membrane. The "SS" prefix refers to Szeto-Schiller, the two investigators (Hazel Szeto and Peter Schiller) who developed the SS series of mitochondria-targeted peptides at Weill Cornell in the early 2000s.
Unlike most peptides in this library, SS-31 is now a regulator-recognized drug. It was approved by the FDA on September 19, 2025 as Forzinity for patients with Barth syndrome, a rare X-linked mitochondrial cardiomyopathy.
History
Szeto and Schiller published the SS-peptide chemistry in the early 2000s, with the foundational pharmacology paper appearing in the Journal of Biological Chemistry in 2004. The compound was licensed to Stealth BioTherapeutics (originally Stealth Peptides), which carried it into clinical trials under the names Bendavia and MTP-131 across multiple indications including reperfusion injury after MI, heart failure, primary mitochondrial myopathy, and Leber hereditary optic neuropathy.
Several of those programs failed to meet primary endpoints — most prominently the EMBRACE-STEMI trial in reperfusion injury and the MMPOWER-3 trial in primary mitochondrial myopathy. The Barth syndrome program, conducted in a much smaller patient population through the TAZPOWER trial and its open-label extensions, ultimately supported the 2025 accelerated approval. A dry AMD program in Phase III is ongoing.
Regulatory status
FDA approved September 19, 2025 as Forzinity for Barth syndrome in patients weighing at least 30 kg, under accelerated approval based on improvements in muscle strength. The approval included priority review and rare pediatric disease designations. Forzinity is supplied as a subcutaneous injection.
Elamipretide is not approved for any other indication. Compounded SS-31 sold through research peptide channels — typically for longevity or recovery-oriented use — is not the same product as Forzinity and is not authorized for clinical administration in the United States.
Mechanism
SS-31 binds cardiolipin, a phospholipid largely restricted to the inner mitochondrial membrane and essential for the assembly and function of the electron transport chain complexes. By stabilizing cardiolipin and preserving cristae architecture, SS-31 has been reported to improve ATP synthesis, reduce reactive oxygen species generation, and protect against the mitochondrial permeability transition that drives cell death after ischemia-reperfusion.
In Barth syndrome — where the TAZ gene mutation causes abnormal cardiolipin remodeling — the rationale is direct: SS-31 binds the structurally abnormal cardiolipin and restores membrane organization sufficient for improved muscle function. The published 168-week TAZPOWER extension data showed sustained improvements in distance walked on the 6-minute walk test and in knee extensor strength relative to a natural history cohort.
Half-life and dosing intervals
Published terminal half-life of subcutaneous elamipretide is approximately 4 hours, with rapid tissue distribution favoring high-mitochondrial-density tissues (heart, kidney, skeletal muscle, retina). It is dosed once daily by subcutaneous injection.
The Forzinity label specifies weight-based once-daily subcutaneous dosing in Barth syndrome. Doses studied in adjacent programs have ranged from 4 mg to 60 mg per day across indications. Investigational research use outside the Barth syndrome label is not supported by approval-grade dose-finding data.
Reconstitution example
Compounded SS-31 is typically supplied lyophilized in 50 mg vials. A 50 mg vial reconstituted with 2 mL of bacteriostatic water yields 25 mg/mL. On a 1 mL U-100 insulin syringe, 8 units (0.08 mL) delivers 2 mg, and 20 units (0.20 mL) delivers 5 mg. Vial's calculator handles the conversion when vial mass and water volume are entered. Approved Forzinity is supplied in a different formulation prepared by the manufacturer.
What to know
- Approved drug, narrow indication. Forzinity is approved only for Barth syndrome. The broader cardiology and ophthalmology programs are either still in development or have read out negative.
- Compounded vs approved. Research-channel SS-31 is not Forzinity. The two products have different formulation and quality histories.
- Common reported side effects. In Barth syndrome trials, the most frequent finding was mild-to-moderate injection-site reactions. Headache and gastrointestinal symptoms were reported less commonly.
- Storage. Lyophilized: refrigerate, protect from light. Reconstituted: refrigerate and use within the stability window provided by the supplier — most compounders cite 14 to 28 days.
- Off-label longevity use. Marketing of SS-31 as a longevity peptide outpaces the human evidence outside Barth syndrome. The mitochondrial mechanism is well characterized; clinical effects in healthy adults have not been demonstrated in controlled trials.
Sources
- 1.Zhao K et al. (2004). Cell-permeable peptide antioxidants targeted to inner mitochondrial membrane inhibit mitochondrial swelling, oxidative cell death, and reperfusion injury. Journal of Biological Chemistry.
- 2.Thompson WR et al. (2024). Long-term efficacy and safety of elamipretide in patients with Barth syndrome: 168-week open-label extension results of TAZPOWER. Genetics in Medicine.
- 3.Sabbah HN (2022). Elamipretide for Barth syndrome cardiomyopathy: gradual rebuilding of a failed power grid. Heart Failure Reviews.
- 4.Hornby B et al. (2022). Natural history comparison study to assess the efficacy of elamipretide in patients with Barth syndrome. Orphanet Journal of Rare Diseases.
- 5.Zhao C, Zhuang X, Gao J (2026). Elamipretide: the first cardiolipin-directed mitochondrial therapeutic for Barth syndrome approved under accelerated approval. Drug Discoveries & Therapeutics.