Quick Facts
Plain-English Summary
SS-31 (elamipretide) is a synthetic tetrapeptide designed from first principles to reach the inner mitochondrial membrane. Unlike most research peptides, it was purpose-built around a mechanistic hypothesis rather than derived from a naturally occurring protein: the alternating aromatic-cationic sequence (D-Arg–dimethyl-Tyr–Lys–Phe) allows the molecule to traverse both the outer and inner mitochondrial membranes and bind selectively to cardiolipin, a phospholipid almost exclusive to the inner membrane. This selectivity is the foundation of everything clinically interesting about the compound.
Cardiolipin is structurally essential to the inner mitochondrial membrane. It anchors the complexes of the electron transport chain (ETC), maintains the curvature of cristae, and supports the efficiency of ATP synthesis. In aging tissue, in heart failure, and in genetic conditions such as Barth syndrome — which involves a mutation in the TAFAZZIN gene causing abnormal cardiolipin — cardiolipin becomes peroxidised and the ETC becomes disorganised. SS-31 intercepts this process: by binding and stabilising cardiolipin, it prevents its peroxidation and helps restore normal mitochondrial architecture.
This mechanism is unusually specific and unusually well-characterised at the molecular level. The compound has been studied in Phase II and Phase III cardiovascular trials (PROGRESS-HF and EMPOWER-HFrEF), a Phase II renal artery stenosis trial (IDENTITY), and received FDA Breakthrough Therapy Designation for Barth syndrome. Of all compounds in the longevity and mitochondria category, SS-31 has the most substantial clinical trial footprint — though results are mixed, and the compound has not achieved regulatory approval for any indication as of 2026.
SS-31 carries more completed human trial data than any other peptide in the longevity-research category. The Breakthrough Therapy Designation for Barth syndrome is a formal FDA recognition that early clinical evidence is compelling. This is clinically meaningful — but it is not a cure for aging, and it does not translate to the broad wellness claims circulating in self-experimentation communities.
Stealth BioTherapeutics, the company that developed elamipretide, faced significant financial difficulties between 2020 and 2022 and ceased operations. This has disrupted the clinical development pipeline despite promising science. The compound is not commercially available as an approved drug.
Mechanism of Action
Proposed mechanisms below are derived from in vitro and rodent studies only. No mechanistic pathway has been validated in a controlled human study.
All mechanistic data is derived from in vitro or rodent studies. Applicability of these pathways in humans is not established.
Animal Data
| Model | Finding | ICPS Status |
|---|---|---|
| Aged mouse skeletal muscle | SS-31 reversed age-related decline in mitochondrial function, reduced oxidative stress markers, and partially restored muscle force generation in 24-month-old mice. Mitochondrial morphology normalised toward that of young animals. Siegel et al. 2013 ↗ | Preclinical |
| Rat myocardial infarction (I/R) | Significant reduction in infarct size when SS-31 administered at reperfusion. Cardioprotection correlated with preserved cardiolipin content and reduced cytochrome c release. Szeto HH 2008 ↗ | Preclinical |
| Mouse model of Barth syndrome | Tafazzin-deficient mice treated with SS-31 showed improved cardiac function, restored ETC complex activity, and normalised cardiolipin profiles. Provided mechanistic rationale for the FDA Breakthrough Therapy Designation. Sabbah et al. 2016 ↗ | Preclinical |
| Rat renal ischaemia | Proximal tubular protection in acute kidney injury models; reduced serum creatinine, preserved tubular architecture, and attenuated mitochondrial swelling. Supported the IDENTITY trial rationale. Szeto HH et al. 2011 ↗ | Preclinical |
| Aged mouse heart | Reduced mitochondrial ROS production and improved diastolic function in aged mice. Used as preclinical justification for Phase III heart failure trials. | Preclinical |
| Dog model of heart failure (HFrEF) | Chronic IV infusion of elamipretide improved left ventricular ejection fraction and reduced adverse remodelling. One of few large-animal cardiac studies for any research peptide. Sabbah et al. 2016 ↗ | Preclinical |
No finding from this section has been replicated in a controlled human trial. Animal-to-human translation for peptides is uncertain and cannot be assumed.
Human Trials
| Trial | Population | Status | ICPS Status |
|---|---|---|---|
| PROGRESS-HF (Phase II) | HFrEF patients; IV elamipretide infusion, randomised, placebo-controlled; n=71. Daubert MA et al., JACC 2020. | — | Positive Phase II |
| EMPOWER-HFrEF (Phase III) | Larger HFrEF trial; SC elamipretide, randomised; n=~300. Gibson CM et al. Primary endpoint: LV remodelling. | — | Mixed Phase III |
| IDENTITY (Phase II) — Renal Artery Stenosis | Patients with atherosclerotic renal artery stenosis; IV elamipretide infusion; n=28. Saad A et al. | — | Positive Phase II |
| Barth Syndrome — FDA Breakthrough Therapy | Rare genetic cardiomyopathy caused by TAFAZZIN mutation; cardiolipin abnormality directly targets SS-31's mechanism. Phase II data supported Breakthrough Therapy Designation. | — | FDA BTD Granted |
| MMPOWER-3 — Primary Mitochondrial Myopathy | Adults with genetically confirmed primary mitochondrial myopathy; SC elamipretide. | — | Did Not Meet Primary |
SS-31 (Elamipretide) has no FDA, EMA, or Health Canada–approved indications and no published Phase III trial data for any condition as of 2026.
Safety & Side Effects
Across completed clinical trials, elamipretide was generally well-tolerated with no dose-limiting toxicities identified at therapeutic doses. No serious adverse events specifically attributable to the compound were reported at rates significantly above placebo in PROGRESS-HF or IDENTITY.
The most consistently reported adverse effect in SC administration trials is injection site reactions — redness, pain, and induration. These were common (reported in up to 40% of SC-dosed participants in some studies) and were the primary tolerability issue with the subcutaneous formulation used in EMPOWER-HFrEF.
- Injection site redness and swelling (consistent with trials)
- Transient fatigue in first days of use
- No pharmacovigilance database exists for SS-31 outside trials
- Long-term safety data in healthy individuals is absent
- No human PK data published for typical self-experimentation doses
- Active or suspected malignancy
- Pregnancy or breastfeeding
- Severe renal or hepatic impairment (no data)
- Children and adolescents (Barth syndrome trials excepted)
- Combination with agents affecting mitochondrial membrane potential
SS-31 (Elamipretide) is not approved by the FDA, EMA, or Health Canada for any medical indication. It is classified as a research compound and is not legal for human therapeutic use in most jurisdictions. Procurement and use outside of registered clinical trials carries regulatory and unknown health risks.
References
Research disclaimer. CompoundProfile publishes summaries of available scientific literature for educational purposes only. This page does not constitute medical advice and should not be interpreted as an endorsement of SS-31 (Elamipretide) for any therapeutic use. Consult a licensed healthcare professional before considering any research compound. All evidence gradings reflect the state of published literature as of August 2026 and are assessed independently by ICPS.
Community Commentary
Selected discussion from r/Peptides · Curated for signal, not volume
The cardiolipin angle is what makes SS-31 genuinely interesting from a basic science standpoint. Most "mitochondria-targeting" compounds don't actually have a well-defined molecular target at the inner membrane — they just accumulate there or act on ROS generally. SS-31 has NMR-validated cardiolipin binding. The dimethyl-Tyr modification is there specifically to enhance that interaction. That's a level of mechanistic precision you almost never see in peptide research. Whether the clinical translation works is a separate question, but the science is not hand-wavy.
Exactly — and the membrane potential-independent uptake is the other part that distinguishes it. Most cationic lipophilic compounds (like MitoQ) depend on the electrochemical gradient to concentrate in mitochondria, which means they accumulate less in dysfunctional mitochondria that have lost membrane potential — exactly the ones you'd most want to treat. SS-31 doesn't have that limitation. It's a genuine design advantage, not marketing.
PROGRESS-HF gets undersold in longevity circles because the audience isn't interested in LVESV endpoints. But for those of us who think about cardiac mitochondrial medicine, it's a meaningful result: a randomised controlled trial showing structural cardiac improvement with a peptide targeting the inner membrane. That's not nothing. The Phase III failure (EMPOWER) is a real setback but doesn't invalidate the mechanism — it might reflect route of administration, patient selection, or endpoint choice as much as anything about the compound itself.
The Barth syndrome angle is the most honest framing for SS-31's clinical potential. In Barth, cardiolipin is structurally abnormal due to TAFAZZIN mutation — it's not just peroxidised, it's malformed. SS-31's binding and stabilisation capacity is exactly what that disease needs, and the mechanistic overlap with the animal models is very tight. The FDA's Breakthrough Therapy Designation reflects that alignment. Stealth's collapse was a tragedy for Barth patients specifically — the compound had a real shot at approval in that orphan indication.
Hard to overstate how much the Phase III pivot to HFrEF and primary mito myopathy muddied the story. Those are broader, heterogeneous populations where cardiolipin pathology is one factor among many. Barth is a monogenic cardiolipin disease. The target-indication fit was much tighter before the company chased larger markets. Classic pharma pipeline problem.
Worth putting SS-31 in context for people who find it through longevity content. It is the most clinically tested peptide in the mitochondria-longevity category, by a significant margin. That's meaningful context. But "most tested" in a category where most compounds have zero human trials still doesn't mean the broad anti-aging claims are supported. The aging data is from aged mice. The human trials target specific diseases with specific mitochondrial pathology. The jump from there to "take SS-31 to slow your aging" is not scientifically supported, even though the underlying science is legitimately compelling.