What is SS-31?
The main facts about SS-31 fit in one table.
| Question | Answer |
|---|---|
| Type | A synthetic peptide of four amino acids |
| Other names | Elamipretide, MTP-131 |
| Family | Szeto-Schiller (SS) peptides |
| Formula | C32H49N9O5 |
| Molecular weight | 639.8 g/mol |
| Where it goes | The inner membrane of mitochondria |
| What it binds | A lipid called cardiolipin |
Sources: PubChem, Elamipretide, CID 11764719, National Library of Medicine. Szeto HH, First-in-class cardiolipin-protective compound as a therapeutic agent to restore mitochondrial bioenergetics, Br J Pharmacol, 2014.
Questions about this guide?
Ask on WhatsAppIts names
You will see this compound under several labels.
- SS-31 is the lab code. SS stands for Szeto-Schiller, after the two scientists whose team made the peptide family.
- Elamipretide is its official generic name, used in trials and by regulators.
- MTP-131 is an earlier development code.
A US prescription medicine now contains elamipretide. We do not name it here, because it is a finished medicine and not what a research supplier sells.
Sources: PubChem, Elamipretide, CID 11764719, National Library of Medicine. US Food and Drug Administration, FDA Grants Accelerated Approval to First Treatment for Barth Syndrome, Press release, 19 September 2025.
Structure
SS-31 has four building blocks, and two of them are unusual.
| Position | Building block | What is special |
|---|---|---|
| 1 | D-arginine | The mirror-image form of arginine, which enzymes break down slowly |
| 2 | Dmt (2',6'-dimethyltyrosine) | A tyrosine with two extra methyl groups on its ring |
| 3 | Lysine | A normal amino acid with a positive charge |
| 4 | Phenylalanine amide | The chain ends in an amide, not an acid |
The pattern alternates. Ring-shaped (aromatic) pieces sit next to positively charged pieces. This mix lets the small peptide pass through cell membranes. PubChem's chemical name confirms the D form at the first position.
Sources: PubChem, Elamipretide, CID 11764719, National Library of Medicine. Szeto HH, First-in-class cardiolipin-protective compound as a therapeutic agent to restore mitochondrial bioenergetics, Br J Pharmacol, 2014.
How it works
A 2014 review by Hazel Szeto, who led the work, sets out the proposed mechanism.
What cardiolipin is
Cardiolipin is a fat-like molecule found only in the inner membrane of mitochondria. It helps fold that membrane into ridges and holds the energy-making protein complexes close together.
Where SS-31 fits
The review reports that SS-31 binds cardiolipin through charge and oil-loving contacts. It also describes how cardiolipin controls a protein called cytochrome c. When the two interact in one way, cytochrome c carries electrons, as it should. In another way, it starts damaging nearby fats. SS-31 is proposed to keep cytochrome c in its normal role.
A 2023 mouse study added a second idea: that elamipretide also binds the protein that moves ADP, a building block of the cell's energy molecule ATP, into mitochondria. These are lab models of how it might act, not proof of what it does in people.
Sources: Szeto HH, First-in-class cardiolipin-protective compound as a therapeutic agent to restore mitochondrial bioenergetics, Br J Pharmacol, 2014. Pharaoh G et al, Geroscience, 2023.
What was studied
This table sorts the key studies by type. It describes what each team measured, not what anyone should expect.
| Year | Type | Who or what | What was measured |
|---|---|---|---|
| 2013 | Animal | Young and old mice | Muscle energy production, one hour after a single treatment |
| 2019 | Animal | Young and old female mice, 8 weeks | Muscle energy, oxidation balance and treadmill endurance |
| 2021 | Human, randomised | 39 healthy adults aged 60 to 85 | Muscle energy capacity after a single administration, and fatigue |
| 2021 | Human, randomised then open label | 12 people with Barth syndrome | Walking distance and a symptom score |
| 2023 | Human, phase 3 | 218 people with primary mitochondrial myopathy | Walking distance and fatigue scores over 24 weeks |
| 2023 | Animal | Young and old mice | How mitochondria take up ADP |
Two of the human trials did not meet their main goals. In the Barth syndrome trial, the randomised first part missed both main goals before an open-label extension. The larger phase 3 trial in mitochondrial myopathy also missed its main goals.
Sources: Reid Thompson W et al, Genet Med, 2021. Karaa A et al, Efficacy and Safety of Elamipretide in Individuals With Primary Mitochondrial Myopathy: The MMPOWER-3 Randomized Clinical Trial, Neurology, 2023. Siegel MP et al, Aging Cell, 2013. Campbell MD et al, Free Radic Biol Med, 2019. Roshanravan B et al, PLoS One, 2021. Pharaoh G et al, Geroscience, 2023.
SS-31 in 2026
Here is where SS-31 stands in 2026, with a source for every line.
| Where | Status | Source date |
|---|---|---|
| United States | Accelerated approval of an elamipretide medicine for Barth syndrome, with a confirmatory trial required | FDA, 19 September 2025 |
| Primary mitochondrial myopathy | Phase 3 trial did not meet its main goals | Neurology, 2023 |
| Registered trials | 21 elamipretide studies listed on ClinicalTrials.gov | Search, 25 October 2026 |
| Australia | No entry for elamipretide, SS-31 or MTP-131 in the Poisons Standard | Poisons Standard, October 2026 |
Barth syndrome is a rare inherited disease of the mitochondria that mostly affects males. The FDA says accelerated approval rests on a measure thought likely to predict benefit. That is why it asked for another trial to confirm it. A 2025 review sums up the Barth syndrome evidence so far.
Sources: US Food and Drug Administration, FDA Grants Accelerated Approval to First Treatment for Barth Syndrome, Press release, 19 September 2025. Karaa A et al, Efficacy and Safety of Elamipretide in Individuals With Primary Mitochondrial Myopathy: The MMPOWER-3 Randomized Clinical Trial, Neurology, 2023. Jacob N et al, Elamipretide in the Management of Barth Syndrome: Current Evidence and a Case Report, Mol Genet Metab, 2025. ClinicalTrials.gov search for elamipretide, run 25 October 2026 (21 registered studies). Therapeutic Goods (Poisons Standard, October 2026) Instrument 2026 (F2026L01327), searched for elamipretide, SS-31 and MTP-131, 26 October 2026: no entry, Federal Register of Legislation, Australian Government.
Medicine or vial?
A regulated medicine and a research vial are not the same thing, even when the molecule shares a name. The approved product is made, tested and labelled under FDA rules for one disease. A research vial is sold for laboratory work and is not approved for anything, anywhere. Nothing on this page suggests otherwise.
Closer to home, our search of Australia's October 2026 Poisons Standard, the national list of scheduled medicines and poisons, found no entry for elamipretide, SS-31 or MTP-131. A missing entry is not a ruling, so we make no statement about where it stands here, legally or in sport.
Sources: US Food and Drug Administration, FDA Grants Accelerated Approval to First Treatment for Barth Syndrome, Press release, 19 September 2025. Therapeutic Goods (Poisons Standard, October 2026) Instrument 2026 (F2026L01327), searched for elamipretide, SS-31 and MTP-131, 26 October 2026: no entry, Federal Register of Legislation, Australian Government.
SS-31 and MOTS-c
Both are studied in mitochondria research, and that is where the likeness ends. MOTS-c occurs naturally. It is 16 amino acids long and coded in mitochondrial DNA. SS-31 is a synthetic four amino acid peptide designed to bind cardiolipin. Our MOTS-c guide covers it in full.
Sources: Szeto HH, First-in-class cardiolipin-protective compound as a therapeutic agent to restore mitochondrial bioenergetics, Br J Pharmacol, 2014. PubChem, Mots-c, CID 146675088, National Library of Medicine. Lee C et al, Cell Metab, 2015.
The research vial
SS-31 is supplied as a freeze-dried powder in a sealed vial. Bachem advises holding freeze-dried peptide in a tightly closed container below -15 °C. Peptide powder tends to soak up moisture from the air, which lowers its content and can cut its stability, so let the vial warm to room temperature in a desiccator before opening. Our guide on how to store peptides explains more.
Ready to order? See SS-31 on our product page. Stock is sold out for now, so orders are taken as pre-orders. Each one ships with tracking out of Traralgon and lands in 2-3 days, for lab research only.
Sources: Bachem, Handling and storage guidelines for peptides, Knowledge Center.
FAQ
What is SS-31?
A synthetic peptide of four amino acids that travels to the inner membrane of mitochondria and binds a lipid called cardiolipin.
Is SS-31 the same as elamipretide?
Yes. SS-31 is the lab code and elamipretide is the official generic name for the same molecule.
Is SS-31 approved?
In the US, a medicine containing elamipretide has accelerated approval for Barth syndrome only. No approval covers research vials, and Australia's October 2026 Poisons Standard has no entry for it.
How is SS-31 different from MOTS-c?
MOTS-c is a natural peptide of 16 amino acids, coded in mitochondrial DNA. SS-31 is lab-made, only four amino acids long, and built to bind cardiolipin inside mitochondria.
Is SS-31 a peptide?
Yes. It is a tetrapeptide. Two of its four building blocks are modified: a D-arginine and a dimethyl tyrosine.
Is SS-31 on the WADA list?
No anti-doping page we read in October 2026 named it. Not being named is different from being permitted in sport.
Sources
- PubChem, Elamipretide, CID 11764719, National Library of Medicine.
- Szeto HH, First-in-class cardiolipin-protective compound as a therapeutic agent to restore mitochondrial bioenergetics, Br J Pharmacol, 2014.
- US Food and Drug Administration, FDA Grants Accelerated Approval to First Treatment for Barth Syndrome, Press release, 19 September 2025.
- Reid Thompson W et al, Genet Med, 2021.
- Karaa A et al, Efficacy and Safety of Elamipretide in Individuals With Primary Mitochondrial Myopathy: The MMPOWER-3 Randomized Clinical Trial, Neurology, 2023.
- Jacob N et al, Elamipretide in the Management of Barth Syndrome: Current Evidence and a Case Report, Mol Genet Metab, 2025.
- Siegel MP et al, Aging Cell, 2013.
- Campbell MD et al, Free Radic Biol Med, 2019.
- Roshanravan B et al, PLoS One, 2021.
- Pharaoh G et al, Geroscience, 2023.
- ClinicalTrials.gov search for elamipretide, run 25 October 2026 (21 registered studies).
- PubChem, Mots-c, CID 146675088, National Library of Medicine.
- Lee C et al, Cell Metab, 2015.
- Therapeutic Goods (Poisons Standard, October 2026) Instrument 2026 (F2026L01327), searched for elamipretide, SS-31 and MTP-131, 26 October 2026: no entry, Federal Register of Legislation, Australian Government.
- Bachem, Handling and storage guidelines for peptides, Knowledge Center.
