What is SS-31?

SS-31 is a synthetic, cell-permeable tetrapeptide that belongs to the Szeto-Schiller (SS) peptides, a family designed to target the inner mitochondrial membrane. ^[10] Its international non-proprietary name is elamipretide. ^[1] Nothing in the body produces it. It entered clinical development with a commercial sponsor, Stealth, in 2010 as its acetate salt, the form the code MTP-131 refers to. ^[3]

Three facts shape everything below. SS-31 is small, at 639.8 g/mol. ^[1] It goes to one place in the cell, the inner mitochondrial membrane. And almost all of its clinical record comes from one sponsor's development programme. Research-grade SS-31 in 10mg vials is in stock with a batch certificate.

SS-31 works, as studied, by concentrating in the inner mitochondrial membrane and binding cardiolipin, a phospholipid found only there. A 2013 paper describes SS peptides crossing the cell membrane and concentrating more than 1000-fold in the inner mitochondrial membrane independently of mitochondrial membrane potential. ^[11] Its inventors report the same potential-independent uptake for the parent peptide SS-02, in contrast with lipophilic cations such as MitoQ. ^[3]

Using a fluorescent analogue of SS-31, Birk and colleagues reported high-affinity binding to cardiolipin in 2013, and found that the SS-31 and cardiolipin complex inhibited cytochrome c peroxidase activity. ^[2] A 2014 review sets out the proposed chain of events: ^[10]

1. Cardiolipin organises the respiratory complexes into supercomplexes and shapes the cristae.
2. The interaction between cardiolipin and cytochrome c decides whether cytochrome c acts as an electron carrier or as a peroxidase.
3. SS-31 binds cardiolipin through electrostatic and hydrophobic interactions and, in the authors' account, keeps cytochrome c in its electron-carrying role.

A 2020 biophysics study from the University of Connecticut found that SS-31 sits in the membrane's interfacial region and changes the surface electrostatics of model and mitochondrial membranes. ^[12] A 2020 study in aged mice and rats reported that SS-31 associated with the adenine nucleotide translocase ANT1 and the mitochondrial ATP synthasome. ^[13]

Most of this mechanism work involves the compound's inventor. The 2020 membrane paper states that Szeto invented the peptides and founded Stealth BioTherapeutics, and that she has financial interests in the company. ^[12]

SS-31 is a linear tetrapeptide with an amidated C-terminus: D-arginine, 2',6'-dimethyltyrosine, lysine, phenylalanine amide. Its inventors' structure table gives it as H-d-Arg-Dmt-Lys-Phe-NH2. ^[3]

The identifiers come from PubChem ^[1] and the sequence and salt form from the inventors' 2014 review. ^[3] We checked each value on 29 September 2026.

SS-31 has a sequence twin. SS-02, also called [Dmt1]DALDA, is H-Dmt-d-Arg-Phe-Lys-NH2: the same four residues in a different order. ^[3] The two therefore share the formula C32H49N9O5 and the same mass, so a mass spectrometry result matching 639.8 g/mol confirms composition, and the HPLC trace and the lab's identity method speak to the rest.

The 2004 paper that introduced this peptide class describes a motif of alternating aromatic and basic residues, with dimethyltyrosine providing the scavenging properties; analogues without Dmt did not inhibit mitochondrial ROS generation. ^[14]

Research on SS-31 runs from cell and animal models of mitochondrial injury and ageing to randomised human trials in rare mitochondrial disease, heart disease and eye disease. The preclinical record is broad and mostly positive. The controlled human record is mostly negative on primary endpoints.

Laboratory and animal studies:

Randomised and open-label human trials:

The Daubert total is our arithmetic: three cohorts of 8 plus 12 on placebo. Every finding above is what a trial reported for its own population using the sponsor's pharmaceutical product.

The regulatory end point came in 2025. A 2026 review in Drugs reports that elamipretide received accelerated approval in the USA in September 2025 for muscle strength in adult and paediatric patients with Barth syndrome. ^[5] A second review adds that the approval requires a confirmatory trial. ^[20] The Drugs review also lists phase 3 development in dry age-related macular degeneration and mitochondrial myopathies. ^[5]

The SS-31 evidence does not show consistent benefit in controlled human trials. Seven of the randomised trials above missed their primary efficacy endpoints, including the phase 3 trial MMPOWER-3, where the authors classed the result as Class I evidence of no improvement in walk distance or fatigue at 24 weeks. ^[4]

Five further limits are worth stating plainly.

1. The positive Barth syndrome data are uncontrolled. The 168-week result comes from an open-label extension with no placebo group, which 10 patients entered and 8 completed. ^[9] The randomised part of the same trial met neither primary endpoint. ^[18]
2. Independence is limited. Stealth BioTherapeutics employees are authors on the TAZPOWER papers and MMPOWER-3. ^[18][4] The inventor founded the company and holds financial interests in it. ^[12]
3. The ageing data come from rodents. The age-reversal findings in the research table are from mice and rats. ^[11][13] No trial reviewed here tested SS-31 on ageing itself in people.
4. The approval is narrow and conditional. It covers one ultra-rare disease in one country, and it was granted on an accelerated basis with a confirmatory trial required. ^[5][20]
5. The trials used the sponsor's product. Purity, identity and peptide content of a research vial are separate questions, and a batch certificate answers them.

Studies of SS-31 most often reported reactions at the site where the study drug was given, mostly rated mild. In MMPOWER-2, these site reactions were the most commonly reported adverse events with elamipretide, at 80%, the majority mild, and no serious adverse events or deaths were reported. ^[7]

The other trials recorded these events:

• Primary mitochondrial myopathy (MMPOWER-3, 218 adults, 24 weeks): the authors report that most adverse events were mild to moderate in severity. ^[4] The abstract gives no percentages.
• Barth syndrome extension (10 patients, up to 168 weeks): site reactions were the most common adverse events. ^[9]
• Dry AMD (ReCLAIM-2, 176 adults, 48 weeks): adverse events were reported in 86% of the elamipretide group and 71% of the placebo group. The most common were site reactions, including itching, pain, bruising and redness. ^[8]
• Leber hereditary optic neuropathy (12 adults, eye drops): most adverse events were mild to moderate and resolved spontaneously, with no serious adverse events reported. ^[19]
• Heart failure, single infusion (36 adults): no serious adverse events; blood pressure and heart rate stayed stable in all cohorts. ^[16]
• Heart failure, 28 days (PROGRESS-HF, 71 adults): rates of study drug-related adverse events were similar across the three groups. ^[17]

These are clinical-trial observations in specific patient populations. Most abstracts give no adverse-event percentages, and exposure ran from a single infusion to 168 weeks.

SS-31 is not named in the Poisons Standard. We searched the June 2026 instrument (F2026L00633), which commenced on 1 June 2026, for elamipretide, SS-31 and MTP-131 and found no entry in any schedule or appendix. ^[21] The only regulatory approval reported in the literature reviewed here is the US accelerated approval of September 2025. ^[5]

For sport, SS-31 is not named on the WADA 2026 Prohibited List, which took effect on 1 January 2026. ^[22] The list's S0 class prohibits at all times any pharmacological substance not covered elsewhere on the List and with no current approval by any governmental regulatory health authority for human therapeutic use. Elamipretide has held a US approval since September 2025. ^[5] WADA revises the List every year, so check the current edition before relying on this.

MOTS-c is a different case: WADA names it under S4.4.1 as an AMPK activator. ^[22] Our guide to Australian peptide law and the Poisons Standard explains what each schedule means and why status is set compound by compound.

SS-31 is a synthetic four-residue peptide that binds cardiolipin, MOTS-c is a 16-amino-acid peptide encoded in mitochondrial DNA, and NAD+ is a coenzyme with no amino acids at all. All three are studied in mitochondrial research.

The molecular weights come from PubChem. ^[1][23][24] MOTS-c was first described in 2015 as a 16-amino-acid peptide encoded by a short open reading frame in the mitochondrial 12S rRNA. ^[25] The other rows come from our own compound checks of 29 September 2026. Our explainers on what MOTS-c is and what NAD+ is cover each in full, and all three sit in our longevity research peptides range.

No published stability study covers lyophilised research-grade SS-31, so general peptide guidance is the reference point. Bachem's handling guide recommends storing lyophilised peptide in a tightly closed container below -15°C for longer storage, with lower temperatures preferred, and says a refrigerator at 4°C suits short-term use. ^[26]

The same guide says peptides containing Asn, Gln, Met, Cys or Trp have limited shelf lives. ^[26] SS-31 contains none of those five residues, which is our reading of its sequence. It is still a peptide, so the guidance above applies in full.

On solvents, the clearest primary detail comes from the 2013 aged-mouse study, which dissolved SS-31 in isotonic saline at a concentration of 0.3 mg/mL. ^[11] SS-31 is also a basic peptide by Bachem's definition: it carries three basic groups (the N-terminal amine, arginine and lysine), no acidic residue and an amidated C-terminus. Bachem notes that peptides with a large share of Arg and Lys residues tend to be soluble at neutral pH, and names PBS at pH 7.0 to 7.4 as the safest diluent for basic peptides where 1 mg/mL or less is enough. ^[26]

We stock BAC Water in 3ml vials for A$8 for laboratory reconstitution. Record the solvent and the resulting mg per mL concentration on the vial label. Our peptide storage guide covers temperatures, light, moisture and labelling for lyophilised and reconstituted peptides.

Peptides Collective sells SS-31 for laboratory research use only, as lyophilised powder in 10mg vials for A$98. Stock ships from Western Australia with tracking.

Every batch is tested by an independent lab before it goes on sale. The certificate reports purity by HPLC and identity by mass spectrometry, and it is published under the batch number printed on the vial. You can search the certificate of analysis library by that batch number and match the report to the vial in your hand.

Read the certificate against the structure table. The identity result should correspond to a peptide of 639.8 g/mol. A spectrum reported as the protonated ion sits about one mass unit higher, near 640.4. Clinical development used an acetate salt, and a salt form adds counter-ion weight to the powder, which is one reason net peptide content is reported separately from purity. Our guide on how to read a peptide certificate of analysis explains the HPLC trace, the mass spectrum and net peptide content. The SS-31 product page links the certificate for the current batch.

SS-31 is a four-residue synthetic peptide that concentrates in the inner mitochondrial membrane and binds cardiolipin. Its preclinical record is broad, its controlled human trials mostly missed their primary endpoints, and its one approval is a conditional US approval for Barth syndrome. In Australia it is not named in the June 2026 Poisons Standard, and WADA's 2026 List does not name it. For a research vial, the batch certificate is the evidence that settles what is in the vial.