SS-31 UK: Research Overview and Legal Status (2026)

Quick answer

What is SS-31?

SS-31 (elamipretide) is a synthetic peptide made of four amino acids. It gathers in the inner mitochondrial membrane and binds a lipid called cardiolipin. It has been studied in cells, animals and human trials. In the US, a prescription form called Forzinity holds accelerated approval for Barth syndrome. In the UK it has no medicine licence and is sold only as a research material.

• Also known as elamipretide, Bendavia and MTP-131
• The bulk of the evidence is animal and cell work, and human trials have given mixed results
• UK status: research use only, with no MHRA licence

Type “SS-31 UK” into Google and you’ll get a wall of shop listings. Very few of them say what the peptide is, what its human trials found or what UK law says about it, and that’s the gap this guide fills.

We start with the molecule and its names, then cover how it binds its target in lab models and what the research shows, including the trials that missed. After that come its single US approval, UK law, sport rules and the checks a batch certificate should pass. Every finding is labelled with the model it came from, whether that’s cells, mice or people.

Apexion supplies SS-31 strictly for laboratory research. It’s sold for lab work alone, with no human or veterinary use, and nothing on this page is medical advice. Read our Research Use Only notice for the full terms.

What Is SS-31?

SS-31 is a synthetic tetrapeptide from the Szeto-Schiller family, named after its designers, the scientists Hazel Szeto and Peter Schiller. It dissolves in water and carries a positive charge. Even so, it crosses cell membranes and builds up in the inner mitochondrial membrane, the folded layer where cells make most of their ATP.

The series began as opioid-receptor research. Schiller had spent years building small peptides that bind opioid receptors, and a few of the designs turned up somewhere nobody expected: inside mitochondria. SS-31 was the one that stood out. Szeto went on to found the company now called Stealth BioTherapeutics, which developed the peptide under the drug name elamipretide. Stealth is now a subsidiary of Mighty Therapeutics.

Field	Detail
Names	SS-31, elamipretide, Bendavia, MTP-131 (US brand: Forzinity)
Sequence	D-Arg-Dmt-Lys-Phe-NH2
Class	Synthetic tetrapeptide (Szeto-Schiller series)
Formula	C32H49N9O5
Molecular weight	~639.8 g/mol (free base)
CAS number	736992-21-5
Research form	Lyophilised powder, commonly as an acetate salt (Forzinity uses the hydrochloride)
Target	Cardiolipin, inner mitochondrial membrane

Is SS-31 the Same as Elamipretide?

Yes, the two names describe one molecule. SS-31 is the laboratory code from the Szeto-Schiller series. Elamipretide is the INN, short for international nonproprietary name, which is the official generic name a drug carries worldwide. Bendavia and MTP-131 are development codes Stealth used in early trials, and Forzinity is the US brand.

Is Elamipretide a Peptide?

Yes. Elamipretide is a peptide of four amino acids joined in a chain. Two of them are modified: D-arginine, the mirror-image form of arginine, and 2′,6′-dimethyltyrosine (Dmt). Its full identity and batch details are on our SS-31 30mg specification and COA page.

How Does SS-31 Work?

In lab models, SS-31 binds cardiolipin, a lipid that is almost exclusive to the inner mitochondrial membrane. That binding is thought to steady the folded cristae and keep the electron transport chain working as a unit. In cell and animal models, it has been linked with lower reactive oxygen species (ROS), the reactive by-products of energy production.

Cardiolipin is an odd lipid. It has four fatty-acid tails where most lipids have two, which gives it a cone shape that helps the membrane fold tightly into cristae. It also acts as a kind of glue for the protein complexes of the electron transport chain, keeping them close enough to pass electrons along.

When cardiolipin is oxidised, that arrangement loosens. In cell and animal studies, the cristae lose their shape, electron flow becomes leaky and ROS output climbs. SS-31’s positive charges and aromatic rings are thought to let it dock on cardiolipin’s negatively charged head group and hold the structure in place.

A common misreading online calls SS-31 a free-radical scavenger. Its Dmt residue can neutralise some radicals in a test tube, but the Szeto 2014 review places its main action at the membrane, protecting cardiolipin before oxidation starts.

A 2020 study in PNAS by Chavez and colleagues added a protein-level picture. Using cross-linking mass spectrometry on mitochondria from mouse heart tissue, the team mapped which proteins lie closest to SS-31. Each partner they found was a protein already known to bind cardiolipin, many of them involved in ATP production.

What Is SS-31 Used For in Research?

SS-31 is a research tool for studying mitochondrial dysfunction. Labs use it in muscle, heart, kidney, eye and nerve models, and in rare mitochondrial diseases. Because it targets one lipid so precisely, it helps researchers test whether cardiolipin damage is behind a change they see in stressed cells or tissue.

Here’s how the main research areas break down by study type:

• Ageing muscle (animal): Campbell and colleagues studied aged mice and measured mitochondrial function and redox balance in skeletal muscle.
• Kidney (animal): Zhu and colleagues’ 2022 review gathered ischaemic, diabetic and drug-induced kidney injury models in rodents and cells.
• Heart (animal and human): mouse heart-failure models came first, followed by human trials in heart attack and heart failure.
• Dry AMD (human): trials in geographic atrophy, the advanced dry stage of age-related macular degeneration.
• Barth syndrome and primary mitochondrial myopathy (human): rare inherited conditions where mitochondria fail, and the setting for SS-31’s biggest trials.

Weight loss doesn’t appear among the conditions studied in its registered human trials.

What Does the Research on SS-31 Show?

The evidence is mixed. There are many animal studies, and most report positive changes within their own models. In people, several trials missed their primary endpoints, and the only approval anywhere is a US accelerated approval for Barth syndrome. The table below keeps each result tied to its study type.

Research area	Study type	What was reported	Status
Ageing muscle	Animal (aged mice)	Better mitochondrial function markers (Campbell 2019)	Preclinical
Kidney injury	Animal and cell	Fewer injury markers across models (Zhu 2022 review)	Preclinical
Heart	Animal; human (EMBRACE STEMI)	Positive in animal models; the human trial missed its infarct-size endpoint	Mixed
Primary mitochondrial myopathy	Human (MMPOWER-3, Phase 3)	Missed both primary endpoints	Negative
Barth syndrome	Human (TAZPOWER)	Randomised phase missed its primary endpoints; open-label extension data supported the US filing	US approval only
Dry AMD	Human (ReCLAIM-2, Phase 2)	Missed primary endpoints; Phase 3 ReNEW under way	In development

Why the gap between mice and people? Three causes keep surfacing. The human trials were small, which makes modest changes hard to detect. Several relied on surrogate endpoints, such as walking distance or muscle-strength scores, which stand in for clinical outcomes and don’t always track them. And a mouse model reproduces one slice of a human disease at best.

The approval itself came from Barth syndrome, a condition caused by faulty cardiolipin, the exact lipid SS-31 targets. That link between mechanism and disease is the clearest thread through the human data.

Reviewers still see room for more work. A 2025 review in the International Journal of Molecular Sciences by Tung and colleagues notes that “Elamipretide has a unique structure allowing for uptake in a variety of cell types,” and calls for further study of broader uses and long-term safety. The full register of trials is on ClinicalTrials.gov.

Is Elamipretide FDA Approved?

Yes, for one use only. On 19 September 2025 the FDA granted accelerated approval to Forzinity (elamipretide HCl) for Barth syndrome in people with a body weight of 30 kg or more. It isn’t approved for anything else, and keeping the approval depends on the results of a confirmatory trial.

The FDA label states the indication as improving muscle strength in Barth syndrome, approved “based on an improvement in knee extensor muscle strength.” That’s an intermediate endpoint, which is why a follow-up study is required. On 8 July 2026, Mighty Therapeutics dosed the first participant in 4TAZPower, a 72-week, placebo-controlled confirmatory trial.

For the patient community, the decision was a milestone. Emily Milligan, Executive Director of the Barth Syndrome Foundation, called approval day “a day to celebrate – although much work remains.”

Elamipretide also holds a US orphan drug designation for Friedreich’s ataxia, granted in 2022. Orphan status supports development for a rare disease, and it carries no approval.

	Research-grade SS-31	Forzinity (elamipretide HCl)
Purpose	Laboratory research only	Prescription medicine for Barth syndrome
Regulator	None as a medicine; sold under research-use terms	US FDA (accelerated approval)
Quality standard	Batch certificate of analysis (COA)	GMP drug manufacturing
UK availability	Sold to researchers	Not licensed in the UK

Is SS-31 Legal in the UK?

It is, as a research material. SS-31 appears on no schedule of the Misuse of Drugs Act 1971, and the MHRA has never licensed it as a medicine. UK suppliers may therefore offer it to laboratories for research, with sale for human use off the table and no NHS or private prescription route.

Three pieces of UK law set the boundaries (checked October 2026):

• Human Medicines Regulations 2012: any product sold with medicinal claims needs a marketing authorisation first. The MHRA has granted none for elamipretide.
• Misuse of Drugs Act 1971: SS-31 doesn’t appear in its schedules.
• Psychoactive Substances Act 2016: this covers substances that affect mental function, and SS-31 has no recorded psychoactive effect.

Europe looks similar. The EMA has given elamipretide an orphan designation for a mitochondrial DNA depletion syndrome, which is a development status with no authorisation behind it.

Are Peptides Legal to Buy in the UK?

For laboratory use, the large majority of research peptides can be bought legally in the UK. A peptide becomes restricted when it’s controlled under drug law, or when it’s sold as a medicine without an MHRA licence. Status varies from one compound to the next, so our guide are peptides legal in the UK goes through each case.

Can You Buy SS-31 Over the Counter?

No. SS-31 isn’t a pharmacy or over-the-counter medicine in the UK, and no UK pharmacy stocks it. UK suppliers sell it only as a research material for laboratories, under terms such as our Research Use Only notice.

Is SS-31 Banned in Sport?

SS-31 isn’t named on the 2026 WADA Prohibited List. WADA’s S0 class catches substances that no government health regulator has approved for therapeutic use in people, and elamipretide has held a US approval since September 2025. WADA approved its 2027 list on 10 September 2026, and it takes effect on 1 January 2027.

In the UK, UK Anti-Doping (UKAD) enforces the WADA list. The current text of each list is published on wada-ama.org, and UKAD sets out how the rules apply in UK sport at ukad.org.uk.

SS-31 vs MOTS-c: What’s the Difference?

SS-31 is a lab-made peptide with a structural job: it holds on to cardiolipin at the inner mitochondrial membrane. MOTS-c comes from the cell itself, coded by a stretch of mitochondrial DNA, and researchers study it as a messenger for metabolism. Both turn up in mitochondrial research, but they answer very different questions.

Three contrasts stand out:

• Origin: SS-31 came from a chemist’s design, while MOTS-c is read from a short open reading frame inside the 12S rRNA gene.
• Size: SS-31 has 4 amino acids and MOTS-c has 16.
• Site of action: SS-31 stays at the inner membrane in lab models, while MOTS-c is studied for signalling that reaches the cell nucleus under stress.

There are no published studies that combine the two. Our MOTS-c vs SS-31 vs NAD+ comparison covers both in detail, and the MOTS-c 40mg specification lists its identity data.

How to Verify Research-Grade SS-31

The first document to check is the batch certificate of analysis (COA). LC-MS should confirm a mass close to 640 Da, which shows up as a singly charged ion at about m/z 640.4. HPLC purity should be listed together with the method used, and every result should belong to the lot printed on the pen or vial label.

Run through this checklist when the COA arrives:

• Lot match: the COA’s lot code is identical to the one on the label.
• HPLC: the purity percentage, plus the column and detection method.
• LC-MS: the measured mass agrees with the expected value for SS-31.
• Named lab and date: the testing laboratory is identified and the report is dated.
• Salt form: acetate or TFA, because the counter-ion changes the weighed mass.
• Storage: sealed, cold and away from light, as the storage and handling guide explains.

Apexion supplies SS-31 as a pre-filled 30mg research pen, made up to order in the UK. Our pen vs vial comparison compares the two formats. For a full walkthrough of certificates, our guides cover how to read a peptide certificate of analysis and how to verify a research peptide batch. You can check a lot number on our batch verification page.

Frequently Asked Questions

The Bottom Line

SS-31 is one of the most studied mitochondria-targeting peptides. It has a deep animal literature, a mixed record in human trials and a single approval, which is US-only, accelerated and limited to Barth syndrome. UK law treats it as a research material, with no medicine licence behind it. Apexion supplies it strictly for laboratory research, with no human or veterinary use.

See the SS-31 30mg specification and COA, or browse the full mitochondria research range.

Disclaimer: This guide is educational content. Apexion Biolabs sells SS-31 to qualified researchers as a laboratory material only. In the UK it holds no MHRA authorisation and has no medicinal status, and it must never be used in humans or animals. The page offers no medical advice and no guidance on dosing or administration.

Sources

• Szeto HH, Birk AV. Serendipity and the discovery of novel compounds that restore mitochondrial plasticity. Clinical Pharmacology & Therapeutics, 2014. PMC4267688
• Tung C et al. Elamipretide: a review of its structure, mechanism of action, and therapeutic potential. International Journal of Molecular Sciences, 2025. PMC11816484
• Campbell MD et al. Free Radical Biology and Medicine, 2019. PMC6588449
• Zhu Y et al. Oxidative Medicine and Cellular Longevity, 2022. PMC9192202
• Chavez JD et al. PNAS, 2020. PMC7334473
• MMPOWER-3 (NCT03323749) and TAZPOWER (NCT03098797), ClinicalTrials.gov
• US FDA. Forzinity (elamipretide) prescribing information, 2025
• UK legislation: Human Medicines Regulations 2012 and Psychoactive Substances Act 2016
• WADA Prohibited List (2026 and 2027)
• UK Anti-Doping