SS-31

What is SS-31?

SS-31 is a small synthetic peptide, four amino acids long, that targets mitochondria, the structures inside cells that produce most of their energy. Its drug name is elamipretide, and it has also been known as Bendavia and MTP-131. The name SS-31 comes from the Szeto-Schiller family of mitochondria-targeting peptides developed by researchers Hazel Szeto and Peter Schiller. Stealth BioTherapeutics has led its clinical development.

In September 2025, elamipretide received FDA accelerated approval as Forzinity, to improve muscle strength in adults and children weighing at least 30 kg who have Barth syndrome². Barth syndrome is an ultra-rare inherited disorder that affects the heart, muscles and immune system, and elamipretide is the first treatment approved specifically for it². It is also in late-stage trials for dry age-related macular degeneration and mitochondrial myopathies². Separately, SS-31 is sold online as a research peptide and promoted for energy, endurance and healthy aging.

How SS-31 works

Mitochondria make energy using a chain of proteins embedded in their inner membrane. That membrane is folded into ridges, called cristae, and its shape depends on a fat molecule called cardiolipin. When cardiolipin is damaged, the energy-making machinery works poorly and leaks harmful molecules known as reactive oxygen species. SS-31 travels into cells, collects on the inner mitochondrial membrane, and sticks to cardiolipin. The idea is that it helps hold the membrane and its machinery in shape, so mitochondria make energy more efficiently and produce less oxidative damage at the source.

In more detail, elamipretide (D-Arg-dimethylTyr-Lys-Phe-NH2) has alternating aromatic and basic residues that give it a positive charge and allow it to cross cell membranes and concentrate in the inner mitochondrial membrane independently of membrane potential. It selectively binds cardiolipin, stabilizing cristae structure, reducing oxidative stress and enhancing ATP production⁵. In heart failure research it is described as stabilizing the cardiolipin-cytochrome c supercomplex³. Barth syndrome is caused by mutations in the TAZ gene that disrupt cardiolipin remodeling, which makes it a logical target for a cardiolipin-binding drug.

What the research shows on SS-31

Preclinical evidence is broad. Animal and cell studies report benefits in models of heart failure, neurodegeneration, ischemia-reperfusion injury, metabolic disease and muscle weakness⁵. In dogs with heart failure it increased ejection fraction, and in rats it prevented harmful heart remodeling³. It has also been studied as a candidate for macular degeneration¹ and kidney disease driven by mitochondrial dysfunction⁶.

Human results have been more mixed. Early phase I and II trials in primary mitochondrial myopathy suggested safety and improvements in six-minute walk distance and fatigue⁸. The larger phase III trial in that condition, MMPOWER-3, did not meet its primary endpoints. In Barth syndrome, the randomized TAZPOWER trial was small and its primary endpoints in the placebo-controlled phase were not met, but patients in the longer open-label extension showed improvements in function and strength. The accelerated approval is tied to improvement in muscle strength, and under that pathway continued approval depends on confirmatory evidence.

In early heart failure trials, elamipretide caused no severe adverse events and showed hemodynamic improvements only at the highest doses, and the authors called for more studies of long-term safety and efficacy³. Clinical programs described in reviews include PROGRESS-HF in heart failure and ReCLAIM in eye disease⁵. For dry macular degeneration, a subcutaneous elamipretide program has advanced to phase 3⁴. There are no trials showing benefit in healthy people, athletes or normal aging.

Studied for: Primary mitochondrial myopathy, Barth syndrome, Age-related muscle decline research.

SS-31 reference data

SS-31 dosage in published research

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How SS-31 is used in practice

As Forzinity, elamipretide is a once-daily subcutaneous injection prescribed by specialists for people with Barth syndrome who meet the weight threshold. Smaller children with Barth syndrome fall outside the current label because of the 30 kg threshold. It is not a general-purpose mitochondrial supplement.

Outside that setting, SS-31 is sold by research-peptide vendors and some longevity and sports clinics, often promoted for energy, endurance or recovery and sometimes paired with MOTS-c. A 2026 sports medicine review included SS-31 among peptides marketed directly to patients through a gray market, noting that rigorous human safety data for such uses are scarce⁷. Gray-market products are not made to pharmaceutical standards, and purity, dose and sterility are unverified. Doses used by consumers are often copied from trial protocols without the monitoring those trials included.

SS-31 risks and side effects

Injection-site reactions are the most common side effect in clinical trials and can include redness, itching, pain and swelling at the injection site. Headache, nausea and dizziness have also been reported. Overall the drug was generally well tolerated in trials, with no major safety signal in early heart failure studies³.

Important unknowns remain. Long-term safety data are limited, especially outside Barth syndrome and in children. Because it is a daily injection, injection-site tolerance can limit long-term use for some people. Drug interactions are poorly characterized. There are no adequate data in pregnancy. For healthy people, the risk-benefit balance is unknown because no benefit has been shown. Gray-market products add risks of contamination, infection at the injection site and wrong dosing.

Reported side effects

Alternatives to SS-31

For Barth syndrome, elamipretide is now the only disease-specific treatment, used alongside standard heart failure care, management of neutropenia, nutrition and physical therapy. For primary mitochondrial myopathies, there is no approved disease-modifying drug for most forms; care relies on exercise programs, physical therapy and supplements such as coenzyme Q10, which have limited evidence.

For dry macular degeneration with geographic atrophy, pegcetacoplan (Syfovre) and avacincaptad pegol (Izervay) are FDA approved, and AREDS2 supplements are recommended for some intermediate disease. For general energy and healthy aging, regular aerobic and resistance exercise is the best-proven way to improve mitochondrial function.

Questions for a clinician

• What evidence applies to my situation, and at what level?
• What established alternatives should I consider first?
• What monitoring would be necessary, and how often?