What it is
SS-31 is elamipretide, a short peptide designed to do something specific: concentrate in the inner mitochondrial membrane, where it interacts with cardiolipin — a lipid essential to how mitochondria generate energy.
That targeting is the whole point of the molecule. Rather than acting broadly, it accumulates where the machinery it is meant to affect actually sits. MOTS-c, the other mitochondrial entry in this library, arrives at the same organelle from the opposite direction. The cell's own general-purpose antioxidant, glutathione, is the broad-acting comparison this molecule was designed not to be.
What makes this entry different
Most compounds in this library were never taken into registered clinical trials by anyone. This one was, by Stealth BioTherapeutics, in two rare genetic diseases of mitochondrial function: Barth syndrome and primary mitochondrial myopathy.
That means there is a real evidence trail — with a real, published miss in it.
What the trials found
Primary mitochondrial myopathy: participants on high-dose subcutaneous elamipretide walked further in a six-minute walk test than those on placebo, and the increase was dose-dependent. A dose-response relationship is one of the stronger signals a trial can produce, because it is hard to explain by chance.
Barth syndrome: in a randomised, double-blind, placebo-controlled crossover trial, neither primary endpoint was met in part 1. In the later open-label phase, 40 mg subcutaneously improved six-minute walk scores with no serious adverse events, and benefit began to accrue after about six months.
Both halves belong in the summary. A trial that misses its primary endpoints and then shows something in an open-label extension is genuinely weaker evidence than one that hits — open-label means everyone knew what they were getting, and a walking test is sensitive to that.
Who was studied
This is the part that does not survive the trip into a vendor listing.
The participants had rare genetic diseases in which mitochondrial function is measurably impaired from birth. Improving a system that is failing is a different proposition from improving one that is working normally.
No trial has examined SS-31 for energy, performance or longevity in healthy people. The compound is marketed for exactly those things, which is what places it among the compounds sold for longevity.
Safety, in context
In the trials, the most common adverse events were headache and dizziness, and the Barth syndrome work reported no serious adverse events.
That is a reassuring profile — for a manufactured pharmaceutical product, at defined doses, in a monitored trial population. It carries over to a research-chemical vial only as far as one is prepared to assume the contents match.
Where it stands
Approved as a medicine: in the United States, for one rare disease. FDA approved elamipretide as FORZINITY on 19 September 2025 (NDA 215244) to improve muscle strength in people with Barth syndrome weighing at least 30 kg. It is an accelerated approval: it rests on knee-extensor strength, an intermediate measure, and continued approval may depend on a confirmatory trial. The label states 40 mg under the skin once daily, and its safety section is built on 12 patients. Nothing in the approval covers energy, performance or longevity.
Sold as: a prescription medicine for Barth syndrome, and separately as a research chemical, for uses no trial has studied.
Within the mitochondrial group, the 24-residue peptide encoded in mitochondrial DNA itself is the opposite case: a large literature, 312 human-tagged papers, and no study anywhere in which it was given to a person.
On the question this compound is actually searched for, the hub that collects the mitochondrial peptides sold for tiredness sets out the one result that matters most: a phase 3 that measured fatigue and walking distance, and missed both.
Last checked
2026-10-03 (approval status); 2026-09-07 (trial record).