Elamipretide (SS-31): The Mitochondria-Targeted Peptide and Its Clinical Record
Most peptides that circulate in wellness conversations are secretagogues, growth-factor fragments, or repair signals. Elamipretide is different in a way worth stating plainly at the outset: it is a clinical-stage drug with a defined molecular target, a decade of trial data, and — as of 2025 — its first FDA approval. It is not a general wellness compound, and the evidence around it is specific, mixed, and disease-bound. This entry is a research log of what has actually been tested and reported.
What it is
Elamipretide is a small aromatic-cationic tetrapeptide (four amino acids) developed by Stealth BioTherapeutics. You will see it under several names in the literature: the research code SS-31, the earlier development code MTP-131, and — following approval — the brand name Forzinity.
Its mechanism is unusual and central to why it exists. Elamipretide binds cardiolipin, a phospholipid concentrated in the inner mitochondrial membrane. Cardiolipin is essential to the structure of the cristae and to the function of the electron transport chain. In diseased or aged mitochondria, cardiolipin can become disorganized, and energy production and membrane integrity suffer. By associating with cardiolipin, elamipretide is proposed to stabilize the inner membrane and support more efficient oxidative phosphorylation. That is the rationale that carried it into trials; the trials are where the story gets more careful.
It is administered by subcutaneous injection, and the pivotal studies used daily dosing (40 mg/day in the myopathy and AMD programs). Peptides with short circulating persistence typically require frequent dosing — you can explore how dosing interval relates to clearance with our half-life calculator, keeping in mind that published pharmacokinetic figures should always be checked against primary sources.
The clinical record
Barth syndrome (TAZPOWER) — the approval
Barth syndrome is a rare, life-limiting genetic disorder affecting a small number of patients (on the order of ~150 identified individuals in the United States), driven by a mutation that disrupts cardiolipin remodeling — making it a mechanistically logical target for a cardiolipin-binding peptide.
In the TAZPOWER program, Stealth reported that knee-extensor muscle strength improved by more than 45%, with a correlated signal on the 6-minute walk test. On the strength of that data, in September 2025 the FDA granted accelerated approval to elamipretide (Forzinity) to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg. This is a genuinely notable milestone: it is described as the first FDA-approved therapy for a mitochondrial disease and the first approved mitochondria-targeted therapeutic. Accelerated approval means continued/confirmatory evidence is expected — it is a conditional milestone, not a closed case.
Primary mitochondrial myopathy (MMPOWER-3) — a negative primary endpoint
The most rigorous efficacy readout came from MMPOWER-3, a pivotal Phase 3, randomized, double-blind, placebo-controlled trial in genetically confirmed primary mitochondrial myopathy. It enrolled 218 participants (109 elamipretide, 109 placebo), dosed at 40 mg/day subcutaneously for 24 weeks.
The result is important to report honestly: the trial did not meet its primary endpoints — neither the change in 6-minute walk test distance nor the total fatigue score on the Primary Mitochondrial Myopathy Symptom Assessment. Elamipretide was well tolerated, with adverse events largely mild to moderate, but the headline efficacy signal was not there.
What kept the program alive were post hoc analyses suggesting benefit in a genetic subgroup — patients with mtDNA replisome/maintenance-related disorders. Those exploratory findings became the rationale for a follow-up Phase 3 trial, NuPOWER, designed prospectively around that subgroup. Post hoc subgroup signals are hypothesis-generating, not confirmatory — the value of NuPOWER is precisely that it tests the hypothesis head-on.
Dry AMD / geographic atrophy (ReCLAIM-2) — mixed
Elamipretide has also been studied in dry age-related macular degeneration with geographic atrophy. The Phase 2 ReCLAIM-2 trial (daily subcutaneous 40 mg over 48 weeks) did not meet its co-primary endpoints (low-luminance visual acuity and geographic-atrophy growth). Prespecified secondary analyses were more encouraging: a reported ~43% reduction in progression of ellipsoid-zone attenuation (a photoreceptor-integrity measure) and a categorical improvement in low-luminance visual acuity. On that basis, Phase 3 trials (ReNEW and ReGAIN) were initiated. As with the myopathy work, the pattern is a missed primary endpoint with a suggestive secondary signal driving further study.
Reading the evidence
The honest summary of elamipretide's record is that its target biology is well-defined and its safety profile in trials has been reasonable, but its efficacy is disease-specific and uneven. It succeeded — under accelerated approval — in Barth syndrome, a disorder that sits directly on its mechanism. It missed primary endpoints in both primary mitochondrial myopathy and geographic atrophy, leaving secondary and post hoc signals to justify continued trials. That is a very different evidence profile from a compound with broad, established benefit, and it is worth resisting the temptation to generalize from one rare-disease approval to mitochondrial "optimization" at large.
For how regulators currently classify this and related compounds, see our FDA status reference, and for the structured profile and sourcing on this peptide, see SS-31. Regulatory status and trial data change; treat everything here as a snapshot to verify.
PepStash is a research log and reference tool. This article is educational and is not medical advice — it does not diagnose, treat, or recommend any protocol. Regulatory status and trial data change; always verify against primary sources and consult a licensed physician before making any decisions about your health.