SS-31 (Elamipretide)

What it is

SS-31 is a very short peptide with an unusual property: in the body it travels precisely to a place that almost nothing else reaches, the inner membrane of the mitochondria.

There it binds to cardiolipin, a lipid that gives this membrane its shape. The inner mitochondrial membrane is heavily folded, like a compressed accordion. The folds are no accident; they enlarge the surface on which energy is produced. Cardiolipin holds the folding together. With age and in certain diseases it breaks down, the folds flatten, and energy production gets worse.

How it is supposed to work

The idea is unusually concrete. Most substances in this field supposedly act on the mitochondria, and that is about as precise as “acts on the body”. Here there is a named target structure, and it can be detected in humans.

If SS-31 stabilizes cardiolipin, the folding is preserved, and energy production is supposed to run better. Exactly this assumption was tested where it would be most likely to hold: in a hereditary disease in which the mitochondria in muscle do not work properly.

What an approval for 150 people means

In September 2025 the US drug regulator approved elamipretide under the brand name Forzinity. It is the first approved therapy ever for a mitochondrial disease, and that is a real turning point in a field in which there had been nothing until then.

The numbers behind it are part of the picture. The substance is approved for Barth syndrome, a hereditary disease that affects about 1 in 350,000 people; about 150 people in the US live with it. The basis is a randomized crossover study with 12 patients that missed its primary endpoints. In the open-label extension, that is, without placebo and without blinding, with 10 patients, knee extensor strength increased. The accelerated approval, which applies to patients weighing 30 kg or more, rests on this. Given how rare the disease is, this is not a scandal but a deliberate trade-off: a placebo-controlled study of sufficient size is not feasible there, and those affected have nothing else. A mitochondrial researcher put it publicly this way: it cannot be compared with a long, blinded study — but the alternative would have been nothing at all.

The leap into the scene

SS-31 is sold as an anti-aging peptide: more energy, better mitochondria, slower aging. What actually exists is something else — a failed phase 3 trial in a muscle disease, a post-hoc subgroup whose follow-up study has been completed but not fully published, and an approval in an ultra-rare hereditary disease based on 10 patients without a control group.

The logic behind the marketing goes: it repairs broken mitochondria, so it makes healthy ones better. This is the same error of reasoning as with insulin, which is lifesaving when the pancreas fails and dangerous when it works. Replacing something that is missing is different from topping up something that is sufficient.

What the studies show

MMPOWER-3 — phase 3 in mitochondrial myopathy

Placebo-controlled, over 24 weeks, in people with primary mitochondrial myopathy, injected under the skin. There were 2 co-primary endpoints: the distance walked in 6 minutes and a fatigue questionnaire. Both were missed; there was no difference from placebo. The treatment was well tolerated, with mostly mild to moderate side effects.

The post-hoc analysis by genotype

After the trial, patients were divided according to which genetic defect each of them had. In patients with defects in the nuclear DNA, walking distance improved by 25 meters versus practically zero on placebo; in an even narrower subgroup it was a 37-meter improvement versus an 8-meter decline. In defects in the mitochondrial DNA nothing was found, partly because there was a strong placebo effect there. This is a post-hoc analysis: anyone who searches the data after a trial almost always finds a group in which something turns up.

Barth syndrome — the basis of the approval

First a randomized crossover study with 12 patients that missed its primary endpoints. In the subsequent open-label extension without placebo and without blinding, with 10 patients, 8 of whom completed it, knee extensor strength increased. The accelerated approval of September 2025, which applies to patients weighing 30 kg or more, rests on this. A confirmatory study with 48 patients has been running since July 2026.

Where the data stop

In healthy people there is only one small study with a single dose: in 39 older adults between 60 and 85 with weak mitochondrial function, energy capacity in the muscle rose briefly; fatigability did not change. A 4-week study in healthy older adults is underway. Everything else comes from disease settings, and the benefit could not be shown in the large controlled trials in myopathy and macular degeneration.

There are aging data in animals, and that is where the attention comes from. In dry macular degeneration, an eye disease, a phase 2 trial with 176 patients missed its primary endpoints. A phase 3 trial is underway. But older people with a disease are, again, not the same as healthy people who want to prevent something. The subgroup finding from MMPOWER-3 is also still a question and not a result; NuPower is meant to answer it. NuPower (102 patients) has been completed since 2024. Full results have not yet been published.

Status, approval and legal

The approval of September 2025 is an American one; it applies under the brand name Forzinity and covers Barth syndrome, nothing else. Anyone citing it as evidence for anti-aging has either not checked or hopes that you will not. What is traded in the scene as vials is not this preparation, and it has not been tested for this purpose either.

Safety

Here the news is comparatively good: in the large trial SS-31 was well tolerated; side effects were mostly mild to moderate. That is more than can be said about most gray-market peptides. The catch lies in what the data refer to: these safety data apply to one company’s preparation under medical supervision. They do not apply to a vial from the internet whose contents nobody knows.

Sources

• Karaa et al., Neurology 2023 (MMPOWER-3, phase 3 trial in primary mitochondrial myopathy)
• Karaa et al., Orphanet J Rare Dis 2024 (post-hoc analysis of MMPOWER-3 by genotype)
• Thompson et al., Genet Med 2024 (open-label extension of TAZPOWER, 10 patients, basis of approval)
• FDA, Drugs@FDA NDA 215244 (approval decision on elamipretide, Forzinity, September 2025)
• ClinicalTrials.gov NCT05162768 (NuPower, trial in the subgroup with defects in the nuclear DNA, completed 2024)
• ClinicalTrials.gov NCT07531251 (4TAZPower, confirmatory study with 48 patients, since July 2026)
• Reid Thompson et al., Genet Med 2021 (TAZPOWER: randomized crossover study with 12 patients and open-label extension)
• Roshanravan et al., PLoS One 2021 (single dose in 39 older adults with weak mitochondrial function)
• ClinicalTrials.gov NCT07275424 (4-week study in healthy older adults, recruiting)
• Ehlers et al., Ophthalmol Sci 2025 (ReCLAIM-2, phase 2 in dry macular degeneration, 176 patients)
• ClinicalTrials.gov NCT06373731 (ReNEW, phase 3 in dry macular degeneration)