Key takeaways
- SS-31 (elamipretide) is a synthetic peptide that binds cardiolipin, a lipid in the inner mitochondrial membrane, with the goal of supporting how mitochondria produce energy.
- It has reached advanced human testing, including phase 3 randomized controlled trials in primary mitochondrial myopathy and phase 2 work in heart failure.
- The results are mixed by condition: several cardiac trials reported improvements in heart measures, while the main mitochondrial myopathy endpoint was not clearly met.
- The research program is active and broad, spanning inherited mitochondrial disease, heart failure, and a large ongoing phase 3 trial in dry age-related macular degeneration.
- Because the evidence varies so much by condition, the science is best read one indication at a time rather than as a single verdict.
What is SS-31?
SS-31 is a small synthetic peptide, also known by the name elamipretide. Unlike many peptides discussed in regenerative medicine, it has been developed and studied as a pharmaceutical candidate and has progressed into formal human clinical trials. Its distinguishing feature is where it goes inside the cell: SS-31 concentrates in the mitochondria, the structures responsible for producing most of a cell's energy.
Mitochondrial dysfunction is thought to contribute to conditions ranging from inherited mitochondrial diseases to certain forms of heart failure, and SS-31 has been studied as a way to support mitochondrial function across several of them. The human picture is mixed, with strong signals in some settings and a key endpoint missed in another.
How it is thought to work
The proposed mechanism centers on a lipid called cardiolipin, which is found in the inner mitochondrial membrane. Cardiolipin helps organize the proteins of the electron transport chain, the machinery that mitochondria use to generate energy. When cardiolipin is disrupted, that machinery can become less efficient and produce more harmful reactive oxygen species.
SS-31 is described as binding to cardiolipin and helping stabilize the inner mitochondrial membrane. A 2025 review in the International Journal of Molecular Sciences laid out this cardiolipin-targeting mechanism and the surrounding trial landscape. The idea is that by supporting cardiolipin and membrane structure, the peptide may help preserve efficient energy production. How well that rationale holds up in people is what the trials set out to test.
What the human trials found
The most prominent test came in MMPOWER-3, a phase 3 randomized controlled trial published in Neurology in 2023 (registered as NCT03323749), which evaluated daily subcutaneous elamipretide against placebo in people with primary mitochondrial myopathy. Randomized controlled trials are the strongest form of clinical evidence, and this was a large one in the disease the cardiolipin-targeting approach was most directly designed for. Its co-primary endpoints, distance on a six-minute walk test and a fatigue score, were not clearly met.
On the cardiac side, the signal has been more encouraging in several respects. A 2017 randomized, placebo-controlled trial in Circulation: Heart Failure reported that a single intravenous infusion of high-dose elamipretide produced favorable reductions in left ventricular end-diastolic and end-systolic volumes compared with placebo in patients with heart failure with reduced ejection fraction, with no serious adverse events. The PROGRESS-HF phase 2 trial, published in the Journal of Cardiac Failure in 2020, further examined the peptide's effects on left ventricular function in the same population.
The program has continued to expand. NuPower (NCT05162768), a phase 3 trial in primary mitochondrial disease caused by nuclear DNA mutations, completed in 2024, and ReNEW (NCT06373731), a large phase 3 trial in dry age-related macular degeneration, is ongoing. Taken together, this is a peptide studied seriously in humans across multiple conditions, with measurable cardiac findings in earlier trials alongside a phase 3 myopathy study whose primary outcomes were not clearly met. That split is why the evidence is best read one condition at a time rather than as a single verdict.
Why these conditions
What ties the indications together is a shared dependence on mitochondrial energy. In inherited mitochondrial myopathy, energy production is impaired at the cellular level. In heart failure with reduced ejection fraction, the heart muscle works under high energy demand, where mitochondrial efficiency is thought to be especially important. In dry age-related macular degeneration, the focus falls on the retina's densely energy-hungry cells. A peptide that aims to protect mitochondrial membranes has a plausible reason to be tested in each.
Interest in mitochondria-targeting peptides also extends to broader questions of aging and tissue energy, since declining mitochondrial function is a recurring theme in longevity research. The published trials, though, concern specific clinical conditions rather than general anti-aging use. Any decision about SS-31 belongs with a qualified physician who can weigh the evidence against an individual's situation.
The evidence
Selected references, each verified against primary sources (PubMed and ClinicalTrials.gov). Explore the full, filterable research library on our Science page.
This article is for educational purposes only and is not medical advice, a diagnosis, or a treatment recommendation. SS-31 is discussed in the context of the published research; inclusion of a study does not imply a guaranteed outcome. Many of these compounds are investigational and not approved for the uses described in all jurisdictions. Any treatment decision should be made with a qualified physician. Individual results vary.