SS-31What the studies show
A four-amino-acid peptide that binds the inner membrane of mitochondria. In 2025 it became the first approved drug for Barth syndrome.
5 min read · Large human trials · Updated November 2026
In short
- Name
- elamipretide (SS-31) (sold by Progression Labs as SS-31)
- Evidence
- Large human trials
- Bottom line
- Mechanism work in cells and rats, a striking single-dose result in old mice, and randomised placebo-controlled trials in two rare mitochondrial diseases that missed their primary endpoints; the approval rests on a surrogate measure in Barth syndrome.
Before you read this
This guide explains what published studies found. That is all it is.
It is not medical advice and it is not instructions for using anything. Where a dose appears, we are reporting what a named study gave the people or animals in it — a fact about the study, not an instruction to you.
The compounds here are not approved by the FDA for use in people and are sold for laboratory research only. A study tells you what happened to the subjects in it; it does not tell you what would happen to you. Talk to a doctor first.
What it is
Elamipretide, also called SS-31, is a chain of four amino acids: D-arginine, a modified tyrosine, lysine and phenylalanine. It was designed in the early 2000s by Hazel Szeto and Peter Schiller, whose work on opioid peptides turned up a compound that collected inside mitochondria instead 1. What makes it unusual is how it gets there. Most molecules aimed at mitochondria rely on the electrical charge across the inner membrane to pull them in; elamipretide binds cardiolipin, a lipid found almost only on that inner membrane, so it arrives whether the membrane is charged or not 1. In the trials described below it was given as a daily injection under the skin. In September 2025 the U.S. Food and Drug Administration granted it accelerated approval, under the brand name Forzinity, for Barth syndrome 2.
The studies below call this molecule elamipretide (SS-31). Progression Labs sells it as SS-31; the guide uses the store's name and the papers use theirs.
The rest of this guide is free
Unlock the SS-31 guide — and every other one
What the studies found, what they didn't, every source linked. Enter your email once; the link we send opens all of them on this device, plus one plain-language study breakdown a week.
Cardiolipin and the electron chain
Cardiolipin is the lipid that holds the respiratory complexes of the inner membrane in their working arrangement. When it is oxidised or lost — in ageing, in tissue starved of blood, and in the genetic disease Barth syndrome — the complexes leak electrons, make less ATP and more reactive oxygen species. A 2013 study showed that SS-31 binds cardiolipin directly, and that in doing so it stops cytochrome c from acting as a peroxidase that oxidises cardiolipin, while letting it keep carrying electrons 1. In rat kidneys deprived of blood supply and then reperfused, the peptide preserved the structure of the mitochondria and the function of the organ 1. A 2014 review by Szeto collects the mechanism work and the animal studies in heart, kidney, muscle and brain 3.
Old mice
The study most relevant to ageing is from 2013. Mice aged 27 months, roughly a person in their eighties, were given a single injection of SS-31, and within an hour their skeletal-muscle mitochondria made ATP more efficiently and the animals ran longer on a treadmill before tiring; the same injection did nothing measurable in 5-month-old mice 4. The authors read this as the peptide restoring a membrane that had drifted out of shape with age rather than adding anything new, which fits the cardiolipin mechanism. In people, the peptide has been tested mainly in diseases of the mitochondria, described next; there is no published trial of it in ordinary ageing that runs longer than a single dose.
Barth syndrome and mitochondrial myopathy
Barth syndrome is a rare genetic disease in which the enzyme that remodels cardiolipin is missing, so the lipid is malformed from birth; it causes heart failure, weak muscles and low neutrophil counts, almost always in boys. TAZPOWER, published in 2021, gave 12 people with Barth syndrome 40 mg of elamipretide a day or placebo for 12 weeks each, in a crossover design. Neither primary endpoint — distance walked in six minutes, and a fatigue score — reached significance in the blinded part of the trial; in the open-label extension that followed, walking distance and strength improved over the following years, which is harder to interpret without a placebo group 5.
Primary mitochondrial myopathy, a group of inherited diseases of muscle energy production, was the other main target. MMPOWER-3, published in 2023, randomised 218 adults to 40 mg a day or placebo for 24 weeks. The trial missed both its primary endpoints: the six-minute walk and a fatigue score did not differ from placebo 6. The most common side effect in both trials was a reaction at the injection site 56.
Approval, and what it rests on
In September 2025 the FDA granted accelerated approval to elamipretide, as Forzinity, for people with Barth syndrome aged 12 and older who weigh at least 30 kg 2. Accelerated approval means the decision rests on a surrogate measure — here, muscle strength — that is considered reasonably likely to predict benefit, and that a confirmatory trial is still owed. It is the first drug approved for the disease. The approval says nothing about ageing, exercise or any other use, and the mitochondrial myopathy trials, which were far larger, did not succeed.
What these studies are, and aren't
Large human trials. Mechanism work in cells and rats, a striking single-dose result in old mice, and randomised placebo-controlled trials in two rare mitochondrial diseases that missed their primary endpoints; the approval rests on a surrogate measure in Barth syndrome.
Sources
- 1Birk AV et al. The mitochondrial-targeted compound SS-31 re-energizes ischemic mitochondria by interacting with cardiolipin. Journal of the American Society of Nephrology, 2013.
- 2U.S. FDA. Novel Drug Approvals for 2025 — Forzinity (elamipretide), accelerated approval for Barth syndrome, September 2025.
- 3Szeto HH. First-in-class cardiolipin-protective compound as a therapeutic agent to restore mitochondrial bioenergetics. British Journal of Pharmacology, 2014 (review).
- 4Siegel MP et al. Mitochondrial-targeted peptide rapidly improves mitochondrial energetics and skeletal muscle performance in aged mice. Aging Cell, 2013.
- 5Reid Thompson W et al. A phase 2/3 randomized clinical trial followed by an open-label extension to evaluate the effectiveness of elamipretide in Barth syndrome, a genetic disorder of mitochondrial cardiolipin metabolism. Genetics in Medicine, 2021.
- 6Karaa A et al. Efficacy and Safety of Elamipretide in Individuals With Primary Mitochondrial Myopathy: The MMPOWER-3 Randomized Clinical Trial. Neurology, 2023.
More in Longevity & mitochondria
- Carnosine: What the Studies ShowA two-amino-acid peptide found in meat extract in 1900, stored in muscle and brain, and raised in trials by feeding one of its two halves.
- Epithalon: What the Studies ShowA four-amino-acid copy of a pineal gland extract, from a St Petersburg laboratory that reported telomerase activation in human cells in 2003.
- Glutathione: What the Studies ShowThe most abundant small antioxidant in human cells: three amino acids joined by a bond that ordinary peptidases cannot cut.
- Humanin: What the Studies ShowA 24-amino-acid peptide encoded inside mitochondrial DNA, found in 2001 in the brain of an Alzheimer's patient and since tied to how long animals live.
- MOTS-C: What the Studies ShowA 16-amino-acid peptide encoded by mitochondrial DNA, not the nucleus, that rises with exercise and kept mice on a high-fat diet from becoming obese.