What SS-31 is. And where it comes from
SS-31 (Szeto-Schiller peptide 31) is a tetrapeptide designed to selectively target the inner mitochondrial membrane. It was developed by Hazel Szeto at Weill Cornell Medical College in the early 2000s. The molecule concentrates approximately 1000-fold inside mitochondria, driven by the organelle's electrochemical gradient.
Its target is cardiolipin. A phospholipid found only on the inner mitochondrial membrane that is essential for electron transport chain function. When cardiolipin is damaged (by aging, disease, or oxidative stress), mitochondrial energy production fails. SS-31 stabilizes cardiolipin, restoring electron transport efficiency and reducing the generation of reactive oxygen species.
Stealth BioTherapeutics licensed SS-31 as Elamipretide and advanced it through Phase II clinical trials for Barth syndrome and primary mitochondrial myopathy.
SS-31 is one of the few peptides in the longevity space that has actually completed Phase II human trials. That puts it far ahead of most compounds discussed in biohacking circles, though it is being developed for rare mitochondrial diseases, not general anti-aging.
Mechanism, in plain English
SS-31 has a specific and well-characterized mechanism centered on mitochondrial membrane biology.
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What the clinical evidence shows
Phase II trials (completed): Elamipretide completed Phase II trials for Barth syndrome (a rare genetic mitochondrial disorder) and primary mitochondrial myopathy (PMM). In Barth syndrome, patients showed improvements in the 6-minute walk test and patient-reported outcomes. The FDA granted Fast Track designation.
Additional clinical data: Phase II trials were also conducted for heart failure with preserved ejection fraction (HFpEF), age-related macular degeneration, and renal function in mitochondrial disease. Results were mixed, some endpoints met, others not.
Anti-aging applications: The interest in SS-31 for general longevity is based on the mitochondrial theory of aging and animal data showing improved function in aged tissues. However, human trials have focused on specific diseases, not healthy aging. Anti-aging use is extrapolation.
Evidence level: ★★★☆☆, preliminary human evidence. Phase II data exists for specific indications. General anti-aging evidence is preclinical.
SS-31 has more human clinical data than 90% of the compounds discussed in the peptide space. But that data is for rare mitochondrial diseases, not for healthy people wanting to slow aging. The leap from treating Barth syndrome to reversing aging is enormous.
FDA status
SS-31 (Elamipretide) is not yet FDA-approved. It has completed Phase II trials and received FDA Fast Track designation for Barth syndrome.
Stealth BioTherapeutics has faced regulatory and financial challenges. The path to approval has been slower than initially expected. The compound is not available outside clinical trials. Last reviewed 2026-08-19.
Common synonyms researchers use
SS-31 · Elamipretide · MTP-131 · Bendavia · Szeto-Schiller peptide 31. Developer: Stealth BioTherapeutics.
Safety & adverse-event landscape
In Phase II human trials, elamipretide was generally well-tolerated. The most common adverse event was injection site reactions. No major safety signals emerged from completed trials.
However, long-term safety data is limited to trial duration. As a compound that modulates mitochondrial membrane biology, theoretical long-term effects on mitochondrial function and cellular metabolism are not fully characterized.
Peptexa is an educational resource. We do not provide dosing guidance, sourcing recommendations, or protocol advice. Always consult a qualified healthcare provider before any decision involving a peptide or therapeutic compound.
Frequently asked questions
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