A tier · strong
Holds a genuine FDA approval and by far the most rigorous trial programme of any compound here, including a fully powered Phase 3 RCT — though that trial and two others missed their primary endpoints, which is why it is not S.
ss-31
Elamipretide is a mitochondria-targeting tetrapeptide that concentrates on the inner mitochondrial membrane by binding cardiolipin, and it received FDA accelerated approval in September 2025 as Forzinity for Barth syndrome. Despite this approval it has failed the primary endpoints of its largest trials, including the 218-patient Phase 3 MMPOWER-3 study in primary mitochondrial myopathy.
the explanation
SS-31 is a small peptide that homes in on mitochondria, the parts of cells that make energy, and it became the first mitochondria-targeting drug ever approved by the FDA in September 2025 for an ultra-rare genetic condition. It has been tested more rigorously than any other peptide on this list, but its biggest trials in heart failure, heart attack and mitochondrial myopathy all failed.
regulatory status
FDA accelerated approval (September 2025)
SS-31/elamipretide was approved 19 September 2025 as Forzinity for improving muscle strength in adult and pediatric Barth syndrome patients weighing at least 30 kg — an accelerated approval on an intermediate endpoint with confirmatory trial obligations, narrower than PT-141's full approval as Vyleesi and unlike Semax and Selank which have no FDA standing at all
how it works · proposed mechanism
Elamipretide works by physically targeting a specific lipid in the inner mitochondrial membrane rather than by receptor binding.
Binds cardiolipin directly
The peptide concentrates in the inner mitochondrial membrane by associating with cardiolipin, a phospholipid essential to cristae structure and respiratory chain organisation. This targeting is what makes it mitochondria-selective without needing a transporter.
Stabilises cristae architecture
By modulating membrane surface electrostatics it helps preserve cristae curvature and the supercomplex organisation of the electron transport chain. In ischaemic tissue this has been shown to re-energise mitochondria.
Improves coupling efficiency
Better-organised respiratory complexes leak fewer electrons, which raises ATP output per unit oxygen and reduces reactive oxygen species generation. This is the basis for its use in mitochondrial disease rather than as a general antioxidant.
Barth syndrome is a cardiolipin disease
Barth syndrome is caused by TAFAZZIN mutations that disrupt cardiolipin remodelling, making it the mechanistically ideal indication. That alignment is likely why this was the indication that succeeded where broader ones failed.
what’s reported
evidence shape
6 sourcesThe composition of the cited literature by study type. This describes the shape of the evidence, not its quality — and it does not by itself set the grade.
⚠ the catch
The approval is real but extraordinarily narrow — an accelerated approval on an intermediate endpoint, from an open-label trial, in a disease affecting roughly 150 people in the United States, with confirmatory trial obligations still outstanding. Everywhere the compound was tested against a broader population it failed: MMPOWER-3 missed both co-primary endpoints in 218 patients, a 71-patient heart failure trial showed no change in left ventricular end systolic volume, and a 118-patient myocardial infarction trial showed no reduction in infarct size.
key published findings
- Human RCT: MMPOWER-3 randomized 218 patients with primary mitochondrial myopathy and missed both co-primaries — 6MWT least-squares mean difference -3.2 m (95% CI -18.7 to 12.3, p=.69) and total fatigue score -0.07 (95% CI -0.10 to 0.26, p=.37) at 24 weeks (Neurology, 2023)
- Human RCT subgroup: post hoc analysis found patients with nuclear DNA defects gained 25.2 m on 6MWT versus placebo (p=.03), described by investigators as hypothesis-generating rather than confirmatory (Orphanet J Rare Dis, 2024)
- Regulatory: FDA granted accelerated approval 19 September 2025 for Barth syndrome in patients weighing at least 30 kg, based on improvement in knee extensor muscle strength as an intermediate clinical endpoint from the open-label TAZPOWER trial, with confirmatory trial obligations
- Human RCT: a 71-patient Phase 2 heart failure trial found no significant change in left ventricular end systolic volume versus placebo at week 4; a 118-patient Phase 2a myocardial infarction trial found no reduction in infarct size
- Preclinical/in vitro: SS-31 re-energizes ischemic mitochondria by interacting with cardiolipin, establishing the mechanistic basis for the compound (JASN, 2013)
limitations of the evidence
- The approval is accelerated and rests on an intermediate endpoint from an open-label trial in roughly 150 US patients; confirmatory clinical benefit has not yet been demonstrated
- Every trial in a broader population — mitochondrial myopathy, heart failure, myocardial infarction — missed its primary endpoint, so efficacy outside Barth syndrome is unsupported
- Independent review notes that treatment durations longer than 4 weeks were not studied in several programmes, and there is no clinical evidence of the cognitive, anti-ageing or general 'mitochondrial health' benefits popularly attributed to it
documented safety signals
- Injection site reactions are the most common adverse event across trials and are the most common adverse event noted in the Forzinity approval
- Adverse events across the trial programme were predominantly mild, but long-term safety beyond trial durations remains incompletely established
- Continued approval is contingent on verification of clinical benefit in confirmatory trials, meaning the benefit-risk balance is not yet settled
identity
| full name | Elamipretide |
| category | Longevity |
| modality | peptide |
| formula | C32H49N9O5 |
| molar mass | 639.8 g/mol |
| cas | 736992-21-5 |
| half-life | ~4 hours (canine preclinical data) |
| sequence | D-Arg-2,6-dimethyl-Tyr-Lys-Phe-NH2 |
laboratory handling
| storage | Approved product is dispensed and stored per the Forzinity prescribing information; lyophilised research-grade material is held at -20°C protected from light, with reconstituted solution refrigerated at 2-8°C and protected from light. |
| solubility | Freely soluble in sterile or bacteriostatic water; the aromatic-cationic tetrapeptide is highly water-soluble. |
Handling information describes laboratory practice for a research reagent. It is not a preparation guide for use in humans.
the receipts
6 citedUS Food and Drug Administration · 2025 · official
Neurology · 2023 · peer-reviewed
Orphanet Journal of Rare Diseases · 2024 · peer-reviewed
Heart Failure Reviews · 2022 · review
Journal of the American Society of Nephrology · 2013 · preclinical
Stealth BioTherapeutics / PR Newswire · 2025 · press release
Sources marked tertiary or press release are the weakest citations on this page.
others in Longevity