Research
What Is SS-31 (Elamipretide)? The Mitochondria Peptide
SS-31 is a small peptide designed to go straight to the mitochondria, the structures that make most of your cell’s energy. It is unusual among popular research peptides because it became an FDA-approved drug: in September 2025, elamipretide (brand name Forzinity) received accelerated approval for a rare disease called Barth syndrome. Here is what SS-31 is, how it works, and what the approval does and does not cover.
Reviewed for accuracy · Last reviewed October 19, 2026
What Is SS-31?
SS-31 is a tetrapeptide (D-Arg-Dmt-Lys-Phe-NH2). The name comes from its inventors, Hazel Szeto and Peter Schiller, who developed a series of “Szeto-Schiller” peptides. It has also been called MTP-131 and, as a drug, elamipretide.
Its structure alternates positive charges and ring-shaped amino acids, which lets it pass through cell membranes and concentrate in the inner membrane of mitochondria.
How Does SS-31 Work?
SS-31 binds to cardiolipin, a fat found almost only in the inner mitochondrial membrane. Cardiolipin holds the energy-making machinery (the electron transport chain) in place. Research suggests SS-31:
- Stabilizes cardiolipin and the shape of the mitochondrial inner membrane.
- Improves ATP production, the cell’s energy currency.
- Reduces reactive oxygen species, harmful by-products of energy production.
What Does the Research Show?
Barth syndrome. Barth syndrome is an ultra-rare genetic disease, affecting about 150 people in the U.S., that disrupts cardiolipin and causes heart and muscle weakness. In the TAZPOWER trial, elamipretide improved knee extensor muscle strength. The FDA granted accelerated approval on September 19, 2025, for patients weighing at least 30 kg, and requires a confirmatory trial.
Other conditions. Elamipretide has also been tested in primary mitochondrial myopathy, heart failure and age-related eye disease. Several of these trials missed their main goals, including a phase 3 trial in mitochondrial myopathy.
Aging research. In older mice, SS-31 improved heart and muscle function, which has fueled interest in longevity circles. These findings have not been tested in healthy older people.
| Area | What studies show | Evidence type |
|---|---|---|
| Barth syndrome | Improved muscle strength; FDA accelerated approval | Human RCT |
| Mitochondrial myopathy | Missed primary endpoint | Human phase 3 |
| Aging heart and muscle | Improved function in old mice | Animal |
| Healthy aging in people | Not studied | Lacking |
SS-31 Side Effects
Because elamipretide is an approved drug, its side effects are better documented than most peptides. In clinical trials, the most common were mild to moderate injection-site reactions such as redness, itching and pain. Serious injection-site reactions and allergic reactions have also been reported, and the drug should not be used by anyone with a known serious allergy to it.
Research SS-31 vs FDA-Approved Forzinity
Forzinity is manufactured under pharmaceutical standards and approved only for Barth syndrome. Products sold as “SS-31” by research suppliers are research chemicals: they are not Forzinity, are not FDA-approved, and their purity depends entirely on the supplier. Third-party testing and a certificate of analysis are the only way to check what is in a research vial.
SS-31 at a Glance
| Detail | Summary |
|---|---|
| Other names | Elamipretide, MTP-131, Forzinity |
| Type | Mitochondria-targeted tetrapeptide |
| Target | Cardiolipin in the inner mitochondrial membrane |
| Developer | Stealth BioTherapeutics |
| FDA status | Accelerated approval (Sept 2025) for Barth syndrome only |
| Main side effect | Injection-site reactions |
SS-31 vs Other Mitochondrial Compounds
SS-31 is often compared with other compounds aimed at mitochondrial health:
| Compound | How it acts on mitochondria | FDA status |
|---|---|---|
| SS-31 (elamipretide) | Binds cardiolipin, stabilizes inner membrane | Approved for Barth syndrome only |
| MOTS-c | Signals from mitochondria via AMPK | Not approved |
| NAD+ | Coenzyme for energy production | Supplement precursors only |
| Methylene blue | Alternative electron carrier | Approved for methemoglobinemia |
| SLU-PP-332 | Increases mitochondrial biogenesis | Not approved |
Why SS-31 is different. Most mitochondrial supplements try to increase fuel or the number of mitochondria. SS-31 instead protects the structure of existing mitochondria. That is why it was tested in diseases where the inner membrane itself is damaged, such as Barth syndrome.
Dosing context. The approved Forzinity dose is a daily injection prescribed and monitored by specialists for a specific genetic disease. That clinical context does not translate to general wellness use.
Buying Research-Grade SS-31: What to Check
Products sold as SS-31 by research suppliers are laboratory chemicals, not medicines. They are not made under drug manufacturing rules, so quality varies a lot between vendors. If you are evaluating an SS-31 supplier for lab research, these are the checks that matter:
- Batch-specific COA: the certificate should match the lot number on your vial, not a generic sample.
- Independent lab: testing should come from a named third-party lab, ideally with a way to verify the report online.
- Identity, not just purity: HPLC purity alone does not confirm the right molecule; look for mass spectrometry (MS) identity confirmation.
- Endotoxin and sterility results: these matter for any injectable research material.
- Correct fill amount: the measured content should be close to the labeled milligrams.
Our Trusted Sources page lists vendors we track, with current community codes. Our guide to reading a certificate of analysis explains each line of a COA.
Key Takeaways
- SS-31 is a four-amino-acid peptide that targets cardiolipin inside mitochondria.
- As elamipretide (Forzinity), it is the first FDA-approved mitochondria-targeted drug.
- Approval covers only Barth syndrome and depends on a confirmatory trial.
- Trials in other conditions have had mixed results.
- Research-grade SS-31 is not the same as the approved drug.
Frequently Asked Questions
What is SS-31?
SS-31 is a four-amino-acid peptide that targets the inner membrane of mitochondria by binding cardiolipin. As a drug it is called elamipretide.
Is SS-31 FDA-approved?
Yes, as elamipretide (Forzinity). It received FDA accelerated approval in September 2025, but only for Barth syndrome in patients weighing at least 30 kg.
Is SS-31 the same as Forzinity?
Forzinity is the FDA-approved, pharmaceutical-grade form of elamipretide. Research products labeled SS-31 are not Forzinity and are not FDA-approved.
What does SS-31 do?
It stabilizes the inner mitochondrial membrane, which may improve energy (ATP) production and reduce oxidative stress.
What are the side effects of SS-31?
The most common in trials were injection-site reactions. Serious injection-site and allergic reactions have also been reported.
Sources
- FDA – FDA grants accelerated approval to first treatment for Barth syndrome (September 2025)
- Stealth BioTherapeutics – Forzinity (elamipretide HCl) accelerated approval announcement
- Forzinity prescribing information, FDA (revised September 2025)
- Szeto (2014) – First-in-class cardiolipin-protective compound as a therapeutic agent to restore mitochondrial bioenergetics
MLCR SCTY provides educational information, not medical or legal advice. Research-use-only products are not intended for human consumption.