TL;DR: SS-31 (elamipretide) is a mitochondria-targeted peptide that binds a fat molecule inside the mitochondrial membrane, aiming to keep the cell's power-generating machinery working properly and cut down on the damaging by-products it produces under stress. Unlike most peptides on this site, it has gone through multiple real Phase 2 and Phase 3 human trials, in Barth syndrome, primary mitochondrial myopathy and a form of age-related vision loss. The FDA granted accelerated approval to Forzinity in September 2025 for a specific Barth syndrome indication. That decision does not establish elamipretide as a general fitness or anti-ageing treatment.
What is SS-31?
SS-31, known clinically as Elamipretide (also referenced in earlier literature as Bendavia or MTP-131), is a synthetic tetrapeptide belonging to the Szeto-Schiller family of mitochondria-targeted compounds, named after its originators Hazel H. Szeto and Peter Schiller. Unlike growth hormone secretagogue peptides, SS-31 is built on an alternating aromatic-cationic amino acid motif that allows it to concentrate selectively in the inner mitochondrial membrane, where it binds cardiolipin — a phospholipid found almost exclusively in that membrane and essential to maintaining the folded cristae structure that supports efficient electron transport chain (ETC) function.
Stealth BioTherapeutics has tested Elamipretide in human trials for Barth syndrome, primary mitochondrial myopathy and dry age-related macular degeneration. Its US regulatory status is indication-specific; an approval in one condition does not establish effectiveness for the other conditions studied. This guide is for educational and research purposes only. Not medical advice.
How strong is the evidence?
| Evidence Type |
Status |
| Human RCT |
✔ |
| Observational |
✔ |
| Animal Studies |
✔ |
| In Vitro |
✔ |
| Regulatory Approval |
US accelerated approval for a specific Barth syndrome indication; see the FDA source below. |
Multiple real Phase 2/3 human randomised controlled trials have been conducted, alongside observational extension studies, animal models, and in vitro cardiolipin-binding work. The FDA approval record dated 19 September 2025 covers improved muscle strength in adults and children with Barth syndrome weighing at least 30kg. Confirmatory clinical evidence is required under accelerated approval. This is not a recommendation for use.
How does SS-31 work?
SS-31/Elamipretide works fundamentally differently from GH-secretagogue peptides such as Ipamorelin or CJC-1295 — it does not act on a cell-surface receptor to trigger a hormonal cascade. Instead, its aromatic-cationic structure allows it to accumulate in mitochondria and bind directly to cardiolipin on the inner mitochondrial membrane. This interaction is thought to stabilise the folded cristae architecture of the membrane, which in turn supports more efficient assembly and function of electron transport chain complexes.
By protecting cristae structure and ETC efficiency, research models suggest SS-31 can reduce electron leakage and the resulting production of reactive oxygen species (ROS), while supporting more consistent ATP synthesis. This positions the compound as a mitochondria-targeted bioenergetics and antioxidant candidate rather than a hormone-modulating peptide, which is why its research programme centres on conditions with a clear mitochondrial or oxidative-stress component — muscle disease, cardiac tissue, and retinal degeneration — rather than growth, body composition, or metabolic peptide-typical endpoints.
What has SS-31 been studied for?
Mitochondrial Bioenergetics & Cristae Structure
The foundational body of SS-31 research is preclinical and in vitro work demonstrating cardiolipin binding, cristae stabilisation, and improved electron transport chain coupling in isolated mitochondria and cell models. These studies form the mechanistic basis for all later clinical trial programmes and consistently show reduced ROS output alongside preserved ATP-generating capacity under stress conditions.
Barth Syndrome Research (TAZPOWER Trial)
The 168-week open-label extension of TAZPOWER (NCT03098797) followed people with Barth syndrome. Ten entered the extension and eight reached week 168. Walking distance and fatigue measures improved from the extension baseline, but this follow-up had no concurrent placebo group. Those observations cannot establish a placebo-controlled treatment effect.
Primary Mitochondrial Myopathy Research (MMPOWER / MMPOWER-3)
The MMPOWER and MMPOWER-3 trials examined Elamipretide in primary mitochondrial myopathy. MMPOWER-3, a Phase 3 trial, is a notable negative result in the peptide's research record: it did not meet its primary endpoint of 6-minute walk distance versus placebo. This is an important and real finding that should not be omitted — it represents one of the clearest signals that, despite strong preclinical rationale, clinical efficacy in this population was not demonstrated at the Phase 3 level.
Ophthalmic Research in Dry AMD
ReCLAIM-2 studied subcutaneous elamipretide in 176 people with dry age-related macular degeneration and geographic atrophy. It did not meet either primary endpoint: change in low-luminance visual acuity or geographic atrophy area. Signals in additional retinal-imaging measures do not turn that into a positive primary result.
What did the studies actually find?
What side effects were reported?
- Injection site reactions / erythema (the most commonly reported adverse event across chronic subcutaneous trials)
- Mild gastrointestinal discomfort (reported in some trial participants)
- Transient headache (infrequent)
In the ReCLAIM-2 trial, adverse events were reported in 86% of the elamipretide group and 71% of the placebo group. Injection-site reactions were the most common events. Safety findings in specific trial populations do not establish safety for fitness or anti-ageing use.
SS-31 at a glance
- CAS Number
- 736992-21-5
- Molecular Formula
- C40H60N10O7
- Molecular Weight
- Approximately 807.98 g/mol (free base; salt forms vary)
- Half-Life
- Short (minutes); typically administered by daily subcutaneous injection in trials
- Synonyms
- Elamipretide, Bendavia, MTP-131
- Research Classification
- Mitochondria-Targeted Tetrapeptide, Cardiolipin-Binding Compound, Szeto-Schiller (SS) Peptide
The research this page cites
- Szeto HH et al. 2014 — First-in-class cardiolipin-protective compound as a therapeutic agent to restore mitochondrial bioenergetics. — British Journal of Pharmacology — [Review / Mechanism]
- 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 — [Open-label extension]
- Karaa A et al. 2023 — Efficacy and Safety of Elamipretide in Individuals With Primary Mitochondrial Myopathy: The MMPOWER-3 Randomized Clinical Trial. — Neurology — [Human RCT]
- Ehlers JP et al. 2024 — ReCLAIM-2: A Randomized Phase II Clinical Trial Evaluating Elamipretide in Age-related Macular Degeneration, Geographic Atrophy Growth, Visual Function, and Ellipsoid Zone Preservation. — Ophthalmology Science — [Human RCT]
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