SS-31

SS-31, known in the scientific literature as elamipretide, is a small lab-made peptide built to travel inside cells and reach the mitochondria, the structures that make a cell's energy. Instead of mopping up damage broadly like many antioxidants, it locks onto a fat molecule inside the mitochondrial membrane and protects it directly. It is the active molecule behind a medicine with accelerated approval in the United States for a rare muscle condition, but larger trials in a broader muscle disease and in heart attack patients did not show the same benefit.

What it is

SS-31 is a very short peptide, just four amino acids long, carrying a structure that is both electrically charged and able to slip through fatty membranes. That combination steers it toward mitochondria, since the inner membrane of a mitochondrion carries a strong electrical pull that attracts this kind of molecule. Once there, SS-31 is proposed to bind cardiolipin, a fat unique to that inner membrane, and shield it from the kind of oxidative damage that can slow down a cell's energy-making machinery.

That targeted approach is what sets SS-31 apart from broader antioxidant compounds in the research literature, and it is also the basis for a medicine built on the same molecule. In September 2025, regulators in the United States granted accelerated approval to an elamipretide-based drug for improving a measure of muscle strength in people with Barth syndrome, a rare, inherited condition that damages heart and skeletal muscle through faulty mitochondria. The maker must still run a further trial to confirm the benefit.

How it is studied

Human research on SS-31 spans a small crossover trial in people with Barth syndrome, a much larger trial in adults with a broader group of inherited muscle diseases, and a trial in people having emergency treatment for a heart attack. Because the peptide is thought to act inside mitochondria rather than at a receptor on the cell surface, much of the underlying laboratory work looks at isolated mitochondria rather than whole animals, with the human trials testing whether that cellular-level protection produces a measurable effect. Two of the three published human trials behind this entry did not meet the main goal they were designed to test.

What studies report

In September 2025, regulators granted accelerated approval to an elamipretide-based medicine for improving a measure of muscle strength in patients with Barth syndrome weighing at least 30 kilograms, describing it as the first approved mitochondria-targeted therapy. [1]
The randomized, placebo-controlled part of the trial behind that approval did not meet its main goals, a walking-distance test and a symptom scale, in 12 patients with Barth syndrome; only in a later unblinded extension, with no placebo group for comparison, did those scores improve. [2]
A larger, 218-patient placebo-controlled trial in adults with a broader group of inherited mitochondrial muscle diseases found no meaningful difference between the drug and placebo in walking distance or tiredness scores after 24 weeks. [3]
A trial in patients having emergency artery-opening treatment for a heart attack found that an infusion of the drug did not reduce the amount of heart muscle damage compared with placebo. [4]

What is not known

Outside the narrow, genetically defined disease behind its approval, the drug's record is weaker than a single approval headline suggests. The larger trial in the wider group of inherited muscle diseases and the heart attack trial both failed on the walking distance, fatigue, or injury measures they were built to test, even though the drug was generally well tolerated. Even the approval-supporting trial rests on an unblinded extension rather than the randomized comparison, so the confirmatory trial regulators required has not yet reported. Broader anti-aging or general cardiovascular claims for the peptide are not supported by any human trial identified in the record behind this entry.

Reported adverse findings

Across the published trials, the most common side effects were mild reactions at the injection site; none of the three trials reported a safety concern that limited the amount given. [1][2][3]

Regulatory status

An elamipretide-based medicine holds accelerated approval from the United States Food and Drug Administration, granted in September 2025, specifically for improving muscle strength in patients with Barth syndrome who weigh at least 30 kilograms. That approval does not extend to any other condition, and elamipretide has no approval anywhere for general anti-aging, cardiovascular, or exercise-performance use.