What it is
SS-31 (elamipretide) is a mitochondria-targeted tetrapeptide, a chain of four amino acids, that binds cardiolipin, a lipid on the inner mitochondrial membrane. It has been studied clinically for mitochondrial diseases, heart failure and age-related decline.
On September 19, 2025, the FDA granted accelerated approval to Forzinity (elamipretide) as the first treatment for Barth syndrome, a rare, serious disease of the mitochondria, in patients weighing at least 30 kg. It is not approved for any other use. In the PeptidesAI encyclopedia it is categorized under immune.
How it's thought to work
Elamipretide is described as concentrating in mitochondria and binding cardiolipin, which is thought to stabilize the electron transport chain (the series of protein complexes that generate cellular energy), improve ATP production and reduce reactive oxygen species. The FDA's announcement describes the approved drug as working by binding to the inner part of the mitochondria, improving mitochondrial structure and function.
What the research says
The FDA's accelerated approval for Barth syndrome is based on improved knee extensor muscle strength, an intermediate clinical endpoint, and the agency requires a post-approval randomized, double-blind, placebo-controlled trial to confirm that the change translates into patient benefit. Results elsewhere have been mixed. The phase 3 MMPOWER-3 trial in 218 people with primary mitochondrial myopathy did not meet its primary endpoints, a 6-minute walk distance and a fatigue score. The phase 2 ReCLAIM-2 trial in dry age-related macular degeneration with geographic atrophy did not meet statistical significance for its primary endpoints, though it reported slower progression of ellipsoid zone loss, an imaging marker of photoreceptor damage, on predefined additional endpoints.
Reported side effects
Injection site reactions were the most common side effect in clinical trials, which the FDA describes as mild to moderate, and the agency notes that serious reactions have also been reported. In the MMPOWER-3 trial, most adverse events were mild to moderate in severity. Long-term data is still developing.
Reconstitution
SS-31 (Elamipretide) is supplied as a lyophilized (freeze-dried) powder and is typically reconstituted with bacteriostatic (BAC) water before use. It commonly comes in 10 mg and 50 mg vials. The amount of peptide in the vial is fixed; the water added only changes how concentrated the solution is.
Worked example. A 10 mg vial is 10,000 mcg. Reconstituted with 2 mL of BAC water, that works out to 10,000 mcg ÷ 2 mL = 5,000 mcg/mL. On a U-100 insulin syringe, where each unit is 0.01 mL, each unit holds 5,000 × 0.01 = 50 mcg. Use the peptide reconstitution calculator to work out the concentration and units for any vial size and water volume.
Important notes
Forzinity (elamipretide) is FDA-approved under accelerated approval for Barth syndrome only, and continued approval may depend on a confirmatory trial. It is not approved for any other use.
Sources
- FDA Grants Accelerated Approval to First Treatment for Barth Syndrome. U.S. Food and Drug Administration, 2025. Announcement
- FORZINITY (elamipretide) for injection, for subcutaneous use - Prescribing Information. U.S. Food and Drug Administration, 2025. Fda label
- Efficacy and Safety of Elamipretide in Individuals With Primary Mitochondrial Myopathy: The MMPOWER-3 Randomized Clinical Trial.. Karaa A et al. Neurology, 2023. Human trial
- ReCLAIM-2: A Randomized Phase II Clinical Trial Evaluating Elamipretide in Age-related Macular Degeneration, Geographic Atrophy Growth, Visual Function, and Ellipsoid Zone Preservation.. Ehlers JP et al. Ophthalmology Science, 2025. Human trial
Frequently asked questions
These questions cover the same ground as the sections above, in a shorter format.
What is SS-31?
A mitochondria-targeted tetrapeptide, also called elamipretide, that binds cardiolipin. The FDA granted it accelerated approval as Forzinity for Barth syndrome in September 2025.
How is SS-31 thought to work?
It is described as concentrating in mitochondria and binding cardiolipin, which is thought to stabilize the electron transport chain, improve ATP production and reduce reactive oxygen species.
What does the research on SS-31 say?
Accelerated approval for Barth syndrome rests on improved knee muscle strength, with a confirmatory trial required. Trials in primary mitochondrial myopathy and dry age-related macular degeneration did not meet their primary endpoints.
What are the reported side effects of SS-31?
Injection site reactions were the most common side effect in trials, described by the FDA as mild to moderate. Serious reactions have also been reported, and long-term data is still developing.
How much is one unit from a 10 mg SS-31 (Elamipretide) vial?
With 2 mL of BAC water, a 10 mg vial is 5,000 mcg/mL, so one unit on a U-100 syringe (0.01 mL) holds 50 mcg.
The full entry, plus the calculator
The PeptidesAI app has the complete encyclopedia entry for SS-31 (Elamipretide) — one of 70 compounds covered — plus the reconstitution calculator, a dose log and reminders. Free to download on iPhone.
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