Scientifically reviewed by Dr Stephan Hansberg
SS-31 (elamipretide): structure, research and FDA status (2026)
SS-31, now known as elamipretide, is a mitochondria-targeted tetrapeptide that became the first FDA-approved treatment for Barth syndrome in September 2025 under accelerated approval. Its identity data, origin, research by model, trial IDs and regulatory status.
Key takeaways
- •SS-31 (elamipretide) is a synthetic tetrapeptide, D-Arg-Dmt-Lys-Phe-NH2, molar mass 639.8 g/mol, designed to concentrate in the inner mitochondrial membrane.
- •It came from the Szeto-Schiller peptide series and is studied for its interaction with cardiolipin, a lipid of the inner mitochondrial membrane.
- •On 19 September 2025 the FDA granted accelerated approval to Forzinity (elamipretide) for Barth syndrome in patients weighing at least 30 kg, with a confirmatory trial required.
- •That approval covers one specific manufactured product for one indication. A research chemical sold as SS-31 is not Forzinity and carries none of its approval.
- •We found no UK or Australian marketing authorisation. It is not named on the WADA 2026 List. Celyfe does not sell SS-31.
What is SS-31 (elamipretide)?
SS-31 is a synthetic four-residue peptide designed to cross cell membranes and accumulate in the inner mitochondrial membrane, where it associates with the phospholipid cardiolipin. Its international non-proprietary name is elamipretide, and in September 2025 the FDA granted accelerated approval to an elamipretide product, Forzinity, for Barth syndrome, a rare inherited mitochondrial disease.
That makes SS-31 unusual in this group: it is both a widely used research tool in mitochondrial biology and the active ingredient of an FDA-approved medicine. The two should not be confused, since the approval applies to the specific manufactured product, its labelled indication and its quality controls.
Identity at a glance
Identifiers checked against PubChem.
| Property | SS-31 / elamipretide |
|---|---|
| Aliases | SS-31, Szeto-Schiller peptide 31, MTP-131, Bendavia, Ocuvia, elamipretide; brand name Forzinity |
| Sequence (4 residues) | D-Arg-Dmt-Lys-Phe-NH2 (Dmt = 2',6'-dimethyl-L-tyrosine; C-terminal amide) |
| Molecular formula | C32H49N9O5 |
| Molar mass | 639.8 g/mol |
| CAS number | 736992-21-5 |
| PubChem CID | 11764719 |
| FDA UNII | 87GWG91S09 |
Origin and discovery
The SS peptides take their name from Hazel Szeto, at Weill Cornell Medical College, and Peter Schiller, who developed the series. In 2004 Zhao, Szeto, Schiller and colleagues described cell-permeable peptide antioxidants that concentrate in the inner mitochondrial membrane, built around an alternating aromatic and basic residue motif with dimethyltyrosine providing radical-scavenging properties.
Later work, including Birk and colleagues in 2013, focused on the interaction with cardiolipin, and Szeto's 2014 review described SS-31 as a first-in-class cardiolipin-protective compound. The compound was developed clinically by Stealth BioTherapeutics under the names MTP-131, Bendavia and finally elamipretide.
What has been studied, by model
Representative studies are below, with model type stated. The approved indication rests on a specific clinical programme, summarised in the next section.
| Research area | Model | Example study (year, PMID) |
|---|---|---|
| Inner-membrane targeting, oxidative cell death, reperfusion models | Cell and animal | Zhao et al., J Biol Chem (2004), PMID 15178689 |
| Cardiolipin interaction in ischaemic kidney | Biochemical and animal | Birk et al., J Am Soc Nephrol (2013), PMID 23813215 |
| Mechanism overview | Review | Szeto, Br J Pharmacol (2014), PMID 24117165 |
| Primary mitochondrial myopathy, crossover trial | Human, Phase 2 | Karaa et al., J Cachexia Sarcopenia Muscle (2020), PMID 32096613 |
| Cancer- and chemotherapy-induced cachexia | Animal (mouse) | Ballaro et al., Cancers (2021), PMID 33670497 |
| Primary mitochondrial myopathy (MMPOWER-3) | Human, Phase 3 | Karaa et al., Neurology (2023), PMID 37268435 |
| Barth syndrome, 168-week open-label extension | Human | Thompson et al., Genet Med (2024), PMID 38602181 |
Human trial status
Elamipretide has one of the largest registered clinical programmes of any peptide on this site. The FDA's accelerated approval cited the TAZPOWER trial, and as a condition of approval the sponsor must run a randomised, placebo-controlled confirmatory trial.
| ClinicalTrials.gov ID | Study | Phase | Status (Oct 2026) |
|---|---|---|---|
| NCT03098797 | TAZPOWER, Barth syndrome | Phase 2/3 | Completed |
| NCT07531251 | 4TAZPower, Barth syndrome | Phase 4 | Recruiting |
| NCT02367014 | MMPOWER, mitochondrial myopathy | Phase 1/2 | Completed |
| NCT03323749 | MMPOWER-3, primary mitochondrial myopathy | Phase 3 | Terminated |
| NCT05162768 | Primary mitochondrial disease from nuclear DNA mutations | Phase 3 | Completed |
| NCT03891875 | ReCLAIM-2, age-related macular degeneration | Phase 2 | Completed |
| NCT06373731 | ReNEW, dry age-related macular degeneration | Phase 3 | Active, not recruiting |
Regulatory status in 2026
The FDA announced the accelerated approval of Forzinity (elamipretide) on 19 September 2025, as the first treatment for Barth syndrome, in patients weighing at least 30 kg. Accelerated approval was based on a surrogate measure, improved strength of the knee extensor muscle, and the sponsor is required to run a further randomised, placebo-controlled trial to confirm it. The application also received priority review.
| Authority | Status (checked October 2026) |
|---|---|
| US FDA | Forzinity (elamipretide) approved 19 September 2025 under accelerated approval for Barth syndrome (patients at least 30 kg); confirmatory trial required. Research-grade SS-31 is not an approved drug. |
| UK MHRA | No UK marketing authorisation identified. In the EU, elamipretide holds an orphan designation (EU/3/22/2614, 2022), which is not an authorisation. |
| AU TGA | Not named in the Poisons Standard (October 2026 instrument); no Australian registration identified. |
| WADA 2026 | Not named on the 2026 List. Because it now has a governmental approval, athletes should check its status with their anti-doping organisation rather than assume S0 applies. |
Stability and handling notes
SS-31 was designed for metabolic stability. Its N-terminal D-arginine and C-terminal amide are classic modifications that make a short peptide a poor substrate for common peptidases, and the dimethyltyrosine is a non-natural residue. Its alternating aromatic-cationic layout gives it a strong net positive charge at physiological pH, which is central to how it associates with the negatively charged cardiolipin.
Because one residue is a D-amino acid, chiral purity is a meaningful quality attribute: the all-L diastereomer has the same mass and would not be distinguished by mass spectrometry alone.
Open questions
Whether the knee-strength surrogate in Barth syndrome translates into the patient outcomes the confirmatory trial must show is the central open question. In other indications the picture is less clear: the Phase 3 MMPOWER-3 trial in primary mitochondrial myopathy did not meet its primary endpoints (Karaa et al., 2023), and the dry AMD Phase 3 (ReNEW) was still active in 2026.
Where Celyfe fits
Celyfe does not sell SS-31 or elamipretide. The only mitochondrial-metabolism compound in the range is NAD+, supplied in the NAD+ Precision Pen (/products/nad-precision-pen) as NAD+ 500mg in a pre-filled 3ml cartridge, with a published batch certificate (batch A26085, Analiza Bialek, HPLC, 99% purity, dated 2 October 2026) in the COA library at /coa.
Sources
Primary and official sources checked October 2026:
- FDA press announcement: FDA grants accelerated approval to first treatment for Barth syndrome, 19 September 2025 (fda.gov)
- PubChem: Elamipretide, CID 11764719 (pubchem.ncbi.nlm.nih.gov)
- Zhao K, Szeto HH, Schiller PW et al. Cell-permeable peptide antioxidants targeted to inner mitochondrial membrane inhibit mitochondrial swelling, oxidative cell death, and reperfusion injury. J Biol Chem, 2004. PMID 15178689
- Birk AV et al. The mitochondrial-targeted compound SS-31 re-energizes ischemic mitochondria by interacting with cardiolipin. J Am Soc Nephrol, 2013. PMID 23813215
- Szeto HH. First-in-class cardiolipin-protective compound as a therapeutic agent to restore mitochondrial bioenergetics. Br J Pharmacol, 2014. PMID 24117165
- Karaa A et al. A randomized crossover trial of elamipretide in adults with primary mitochondrial myopathy. J Cachexia Sarcopenia Muscle, 2020. PMID 32096613
- Ballaro R et al. Targeting mitochondria by SS-31 in cancer- and chemotherapy-induced cachexia (mouse). Cancers, 2021. PMID 33670497
- Karaa A et al. Efficacy and safety of elamipretide in individuals with primary mitochondrial myopathy: the MMPOWER-3 randomized clinical trial. Neurology, 2023. PMID 37268435
- Thompson WR et al. Long-term efficacy and safety of elamipretide in patients with Barth syndrome: 168-week open-label extension results of TAZPOWER. Genet Med, 2024. PMID 38602181
- ClinicalTrials.gov records NCT03098797, NCT07531251, NCT02367014, NCT03323749, NCT05162768, NCT03891875, NCT06373731
- EMA: Orphan designation EU/3/22/2614, elamipretide (ema.europa.eu)
- WADA: Prohibited List 2026, in force 1 January 2026 (wada-ama.org)
Research use only
Celyfe supplies research peptides for laboratory and research use only. Nothing on this page is guidance on use in humans or animals.
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