Moderate EvidencePeptide

SS-31 (Elamipretide)

Forzinity

Mitochondria-Targeting Tetrapeptide

Last updated: August 2026

Evidence Level: Moderate Evidence

Some human data, strong animal studies, plausible mechanism

Regulatory Status: FDA accelerated approval September 19, 2025 as Forzinity, for improving muscle strength in patients with Barth syndrome weighing at least 30kg. No approval for any other indication.

SS-31, now called elamipretide, is a four-amino-acid peptide that concentrates inside mitochondria and binds cardiolipin, a lipid essential to energy production. In September 2025 it became the first drug approved to directly target mitochondria, under accelerated approval for Barth syndrome, an ultra-rare genetic disease. That approval is narrow, and the trial behind it is worth reading carefully.

How It Works

Most compounds marketed for "mitochondrial support" do not actually get into mitochondria in meaningful concentrations. SS-31 does, and the reason is structural.

How it gets there. SS-31 carries alternating aromatic and positively charged residues. The inner mitochondrial membrane is strongly negatively charged, so the peptide is drawn to it and accumulates there at concentrations far above what is present in the rest of the cell. This is genuine targeting, not a marketing claim.

What it binds. Cardiolipin, a lipid found almost exclusively in the inner mitochondrial membrane. Cardiolipin organizes the protein complexes of the electron transport chain, the assembly line that turns food and oxygen into usable energy. When cardiolipin is damaged or abnormal, that assembly line becomes inefficient and leaks reactive oxygen species, which damages more cardiolipin. It is a self-reinforcing failure loop.

SS-31 binds cardiolipin and appears to stabilize its structure, improving the efficiency of the electron transport chain and reducing the leakage. Rather than mopping up free radicals after the fact, as antioxidant supplements attempt to do, it targets the place they are produced.

Why Barth syndrome. Barth syndrome is a rare X-linked genetic disorder in which a gene called tafazzin is defective. Tafazzin remodels cardiolipin. So Barth syndrome is, at the molecular level, a cardiolipin disease, which makes it the most logical possible test case for a cardiolipin-binding drug.

Read the approval honestly. The FDA granted accelerated approval on September 19, 2025, based on the TAZPOWER trial, a randomized double-blind placebo-controlled crossover study in 12 patients. Twelve. In that randomized portion, elamipretide did not significantly improve the six-minute walk distance or total fatigue score compared with placebo. Knee extensor muscle strength improvement was observed during the open-label extension, with 8 participants continuing to week 168. The FDA advisory committee voted 10 to 6 in favor.

That is an approval built on a very small trial that missed its randomized endpoints, with the supporting evidence coming from open-label follow-up. Accelerated approval exists precisely for situations like this: an ultra-rare disease with no other treatment, where waiting for a large trial is not realistic. It is a reasonable regulatory decision. It is not the same thing as strong evidence, and it is certainly not evidence for anything outside Barth syndrome.

On the anti-aging pitch. Mitochondrial dysfunction is a recognized hallmark of aging, and SS-31 has been studied in aged mice with encouraging results. Elamipretide has also been tested in humans for primary mitochondrial myopathy and heart failure, where results have been mixed to disappointing. The approval it earned is for a single ultra-rare genetic disease, and using it as evidence for healthy aging is a much longer leap than the marketing suggests.

Evidence by Outcome

Each claim below is rated using a GRADE-aligned five-tier system. Same molecule, different outcomes, different evidence.

Evidence at a glance

How we grade

Muscle preservationLow
Longevity biomarkersPreclinical

Want to see how this compares to every other peptide? Browse the full evidence matrix, where every graded claim is grouped by outcome and sorted by certainty.

Muscle preservationLow certainty

Improves muscle strength in patients with Barth syndrome.

Population: Patients with genetically confirmed Barth syndrome weighing at least 30kg

Why this rating

This claim carries an FDA accelerated approval, which is a meaningful regulatory judgment. The underlying evidence is weak in absolute terms: a randomized crossover trial of 12 patients that did not meet its randomized endpoints, with the strength benefit emerging in an uncontrolled open-label extension. Accelerated approval is designed for exactly this situation, an ultra-rare disease with no alternative, and the FDA advisory committee split 10 to 6. We grade the evidence, not the regulatory decision.

GRADE downgrade factors applied

Imprecision: Wide confidence intervals or small sample size, the estimate could be substantially different.
Risk of bias: Methodological flaws in the studies (e.g. lack of blinding, allocation concealment, high attrition).

Supporting studies

TAZPOWER trial and FDA integrated reviewRandomized Controlled Trial
US Food and Drug Administration2025n=12
Randomized endpoints not met; strength benefit observed in open-label extension. Accelerated approval granted September 19, 2025.

Reviewed 2026-08-24· Designing Longevity EditorialHow we grade

Longevity biomarkersPreclinical certainty

Improves mitochondrial function or physical performance in healthy aging adults.

Population: Healthy older adults. This population has not been studied.

Why this rating

Aged mouse studies showed restoration of some mitochondrial function, which is the basis for the anti-aging interest. No trial has tested elamipretide in healthy aging adults. The most relevant human data comes from trials in primary mitochondrial myopathy and heart failure, where results were mixed to disappointing, which argues for caution rather than optimism about broader use.

Supporting studies

Elamipretide in aged animal modelsAnimal Study
Improved mitochondrial function and some measures of physical performance in aged mice.

Reviewed 2026-08-24· Designing Longevity EditorialHow we grade

Potential Benefits

The first drug ever approved to directly target mitochondria, which is a genuine scientific milestone
FDA-approved, so an actual manufacturing standard and known dose exist for the approved indication
Real mitochondrial targeting through cardiolipin binding, not a generic "mitochondrial support" claim
Addresses the source of reactive oxygen species production rather than scavenging them downstream
Encouraging results in aged animal models, including restoration of some mitochondrial function
Extensive human safety exposure from multiple clinical trial programs

Risks & Considerations

The approval covers Barth syndrome only, an ultra-rare genetic disease. Everything else is unstudied or unsuccessful
The pivotal trial enrolled 12 patients and did not meet its randomized endpoints for walk distance or fatigue
The supporting strength benefit came from an open-label extension, which has no control group
Trials in primary mitochondrial myopathy and heart failure have produced mixed to disappointing results
No trials in healthy aging, despite that being the main reason people seek it out
As a rare disease drug, cost is likely to be prohibitive outside the approved indication
Gray-market "SS-31" is not the approved product and carries no purity or identity verification

Dosing Information

Elamipretide has an approved label for Barth syndrome. Any other use is unstudied, and the doses circulating in the peptide market do not correspond to the approved product.

•Approved for patients with Barth syndrome weighing at least 30kg, administered subcutaneously once daily per the label
•The TAZPOWER trial used 40mg subcutaneously once daily
•Gray-market protocols suggest 5 to 10mg daily, which does not match the approved dosing
•Doses used in heart failure and mitochondrial myopathy trials varied by route and indication
•The approved product is Forzinity. Nothing sold as "SS-31" online is that product

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Practical Tips

1If you or a family member has Barth syndrome, this is now an approved treatment and worth discussing with your specialist
2For general anti-aging, understand that you would be extrapolating from a 12-person trial in an unrelated genetic disease
3The mixed results in heart failure and mitochondrial myopathy are the most relevant data for non-Barth use, and they are not encouraging
4If mitochondrial function is your interest, exercise remains the only intervention with robust human evidence for improving it
5Watch for results from any ongoing trials in broader populations before drawing conclusions

Key Research

FDA integrated review, elamipretide (NDA 215244)

US Food and Drug Administration, 2025

FDA granted accelerated approval on September 19, 2025 for improving muscle strength in Barth syndrome patients weighing at least 30kg. The advisory committee voted 10 to 6 in favor.

View Study

TAZPOWER: elamipretide in Barth syndrome

Randomized double-blind placebo-controlled crossover trial

In the randomized portion, elamipretide did not significantly improve six-minute walk distance or total fatigue score versus placebo. Knee extensor muscle strength improvement was observed during the open-label extension, with 8 participants continuing through week 168.

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Frequently Asked Questions

Is SS-31 FDA-approved?

Yes, for one thing. The FDA granted accelerated approval on September 19, 2025 for elamipretide, sold as Forzinity, to improve muscle strength in patients with Barth syndrome weighing at least 30kg. That is the only approved indication. It is the first drug ever approved that directly targets mitochondria, which is a genuine milestone, but the approval is narrow.

How strong is the evidence behind the approval?

Weaker than the word "approved" suggests. The pivotal TAZPOWER trial was a randomized crossover study in 12 patients, and in the randomized portion elamipretide did not significantly improve six-minute walk distance or fatigue versus placebo. The muscle strength benefit appeared in the open-label extension, which has no control group. The FDA advisory committee voted 10 to 6 in favor. Accelerated approval exists for ultra-rare diseases where a large trial is not feasible, and this is a reasonable use of it, but it is not strong evidence.

Does SS-31 work for anti-aging?

Nobody has tested it in healthy aging adults. The interest comes from aged mouse studies showing improved mitochondrial function, and from the fact that mitochondrial decline is a recognized hallmark of aging. The most relevant human data comes from trials in primary mitochondrial myopathy and heart failure, where results were mixed to disappointing. That should temper expectations considerably.

What does SS-31 actually do to mitochondria?

It accumulates inside mitochondria because of its charge, then binds cardiolipin, a lipid found almost exclusively in the inner mitochondrial membrane. Cardiolipin organizes the protein complexes that produce energy. When it is damaged, energy production becomes inefficient and leaks reactive oxygen species, which damages more cardiolipin. SS-31 appears to stabilize cardiolipin and interrupt that loop at the source.

What is Barth syndrome and why was SS-31 tested for it?

Barth syndrome is a rare X-linked genetic disorder caused by a defect in the tafazzin gene, which remodels cardiolipin. At the molecular level it is a cardiolipin disease, which makes it the most logical possible testing ground for a drug that binds cardiolipin. It causes heart muscle disease, muscle weakness, and low white blood cell counts.

Is SS-31 the same as MOTS-c or humanin?

No. MOTS-c and humanin are peptides your mitochondria actually encode and release as signals. SS-31 is a synthetic peptide designed to travel into mitochondria and bind a structural lipid. Different origins, different mechanisms. SS-31 is the only one of the three with any regulatory approval.

Can I buy SS-31?

The approved product is Forzinity, prescribed for Barth syndrome, and as a rare disease drug it is expensive and tightly distributed. Material sold online as "SS-31" is not that product and carries no verification of identity, purity, or dose. Given how narrow and how weak the actual evidence is, this is a compound where the gap between the science and the sales pitch is unusually wide.

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