SS-31 (Elamipretide)

SS-31 (also Elamipretide, MTP-131, Bendavia) is a synthetic mitochondria-targeted tetrapeptide that selectively binds cardiolipin in the inner mitochondrial membrane, restoring cellular energy production and reducing oxidative stress. It is the most clinically-advanced compound in the mitochondria-targeted peptide class, with Phase 3 trials completed for Barth syndrome and ongoing development for other mitochondrial disease indications. SS-31 became the first approved drug in the mitochondria-targeted peptide class on September 19, 2025, when the FDA granted accelerated approval to elamipretide as FORZINITY (Stealth BioTherapeutics) to improve muscle strength in patients with Barth syndrome weighing at least 30 kg. Research-grade "SS-31" sold by peptide vendors is not the approved FORZINITY product.

Source: FDA approval letter — FORZINITY (elamipretide), NDA 215244, FDA, via Drugs@FDA

What is SS-31 and how does the mitochondria-targeted cardiolipin mechanism work?

SS-31 (Elamipretide) is a synthetic tetrapeptide (D-Arg-2'6'-dimethylTyr-Lys-Phe-NH₂) designed to cross cell and mitochondrial membranes and selectively bind cardiolipin in the inner mitochondrial membrane, where it stabilizes electron transport chain function and reduces reactive oxygen species production. Cardiolipin is the signature mitochondrial phospholipid required for cristae structure and Complex I-V function; SS-31 binding protects cardiolipin from peroxidation.

Evidence level: FDA-approved (accelerated) for Barth syndrome; human RCT; preclinical extensive across mitochondrial disease models

What does the clinical evidence show for SS-31?

In Barth syndrome — a rare X-linked cardiolipin-remodeling disorder — the TAZPOWER trial's improvements in knee-extensor muscle strength supported FDA accelerated approval of elamipretide (FORZINITY) on September 19, 2025; continued approval may be contingent on confirmatory-trial verification of clinical benefit. Outside Barth syndrome the record is weaker: elamipretide's larger programs in heart failure, ischemia-reperfusion injury, and primary mitochondrial myopathy (PROGRESS-HF, EMBRACE-STEMI, MMPOWER-3) did not meet their primary endpoints. Phase 2 trials have explored SS-31 in age-related macular degeneration, primary mitochondrial myopathy, and heart failure with mixed but generally favorable results. The Barth syndrome indication represents the most advanced regulatory pathway.

Sources: FDA approval letter — FORZINITY (elamipretide), NDA 215244, FDA, via Drugs@FDA; EMBRACE STEMI study: a Phase 2a trial to evaluate the safety, tolerability, and efficacy of intravenous MTP-131 on reperfusion injury in patients undergoing primary percutaneous coronary intervention, Gibson C.M. et al., Eur Heart J, 2015 · Evidence level: FDA-approved (accelerated, Barth syndrome); Phase 2/3 in other indications did not meet primary endpoints

How does SS-31 compare to other mitochondria-targeted compounds?

SS-31 has the most advanced clinical development of any mitochondria-targeted peptide, distinguished by the specific cardiolipin-binding mechanism that differentiates it from broader antioxidants and from non-mitochondrial-targeted compounds.

What are the documented side effects of SS-31?

SS-31's safety profile in Phase 2 and Phase 3 trials has been favorable — common side effects include mild injection-site reactions and occasional gastrointestinal events. Discontinuation rates due to adverse events have been low across trials. The targeted mitochondrial mechanism appears to avoid the broad off-target effects associated with non-selective antioxidants.

Evidence level: phase 2/3 human safety; cumulative trial data substantial

What is the regulatory status of SS-31?

Elamipretide is FDA-approved as FORZINITY (September 19, 2025, accelerated approval) for one indication only: improving muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg, dosed subcutaneously once daily. Accelerated approval means continued approval may be contingent on verification of clinical benefit in confirmatory trials. It is not approved for any other indication — including the longevity, energy, and heart-failure uses discussed in research communities — and no other regulator has approved it for those uses as of August 2026. Research-grade SS-31 sold by third-party vendors is a separate supply chain from the prescription product and carries none of its pharmaceutical quality controls. Current status in FDA peptide regulation 2025–2026 timeline.

Source: FDA approval letter — FORZINITY (elamipretide), NDA 215244, FDA, via Drugs@FDA

Why does SS-31 vendor verification matter despite the pharma-sponsored development?

Because the Stealth BioTherapeutics-sponsored clinical material is not the research-grade SS-31 sold by third-party laboratories — those are different supply chains. Research-grade SS-31 is subject to wider purity variance, occasional underdosing, and inconsistent endotoxin control. Independent HPLC purity testing and mass spectrometry identity confirmation are the meaningful purity signals for research-grade material. Guidance in how-to-test-peptides hub.

How does Peptigrity verify SS-31 vendors?

Peptigrity collects independent third-party Certificates of Analysis for SS-31 from shops' official channels and verifies each for authenticity before publishing. Because shops choose which COAs to publish, results reflect the batches shops have made public rather than every production batch — a selection bias we state openly. A community-funded Testing Grant to purchase and test vials anonymously is in development. Tests in the database come from independent labs such as Janoshik Analytical, Freedom Diagnostics, and Chromate. The lab test table above this section shows the cross-shop dataset. Methodology in how we calculate trust scores.

Frequently asked questions

What does SS-31 do?

SS-31 binds cardiolipin in the inner mitochondrial membrane, stabilizing electron transport chain function and reducing oxidative stress, with Phase 3 clinical evidence in Barth syndrome and Phase 2 evidence across multiple mitochondrial disease indications.

Is SS-31 FDA-approved?

Yes — for one rare disease. Elamipretide received FDA accelerated approval as FORZINITY on September 19, 2025, to improve muscle strength in patients with Barth syndrome weighing at least 30 kg. It is not approved for any other indication, and research-grade SS-31 sold by peptide vendors is not the approved product — verifying identity and purity through independent lab tests remains essential. It is among the most advanced non-FDA-approved compounds on Peptigrity in terms of regulatory pathway.

Is SS-31 legal to purchase?

SS-31 is legal to purchase as a research chemical for laboratory use in most jurisdictions, but it is not approved for human consumption. Country breakdown in peptide legal status guide.

How does SS-31 compare to NAD+ for mitochondrial support?

SS-31 targets the mitochondrial membrane specifically (cardiolipin binding, ETC stabilization); NAD+ supports cellular energy more broadly (sirtuin activation, redox reactions). They engage different aspects of mitochondrial function and are not mechanistically interchangeable.

How can I verify an SS-31 vendor is selling real product?

Independent third-party HPLC certificate of analysis from a lab the vendor does not own or pay, with mass spectrometry identity confirmation. COA interpretation in red flags in peptide certificates of analysis.

Does Peptigrity recommend an SS-31 dose?

No. SS-31 is not approved for human consumption and Peptigrity is an independent review platform, not a medical authority. Clinical trial dosing has varied by indication. Anyone considering use should consult a licensed physician.

This section is for educational and informational purposes only and does not constitute medical advice. SS-31 (Elamipretide) is not currently FDA-approved but is in formal clinical development by Stealth BioTherapeutics. Always consult a qualified healthcare provider before using any peptide or research compound. Peptigrity is an independent review platform and does not sell, endorse, or recommend specific products or vendors.