What Is SS-31?
SS-31 is elamipretide, a small synthetic peptide (four amino acids) designed to reach mitochondria, the energy-producing parts of cells. It's named after its developers, Szeto and Schiller. Elamipretide is its drug name.
The big news: on September 19, 2025, FDA granted accelerated approval to Forzinity (elamipretide) injection as the first treatment for Barth syndrome, a rare, life-threatening genetic disease of the mitochondria. That makes SS-31 one of the few "research peptides" that has become an approved medicine, but only for one rare disease.
This is an educational explainer. It doesn't give dosing advice. Talk with a licensed clinician about any treatment.
How SS-31 Works: Cardiolipin
Elamipretide's label calls it a "mitochondrial cardiolipin binder." Cardiolipin is a fat molecule found almost only on the inner mitochondrial membrane. It helps hold the energy-making machinery together. A 2014 review by Hazel Szeto describes how cardiolipin damage is linked to energy failure in many diseases, and how SS-31 was designed to bind and protect it.
In plain English, the idea is to help mitochondria make energy more efficiently when cardiolipin is damaged. That's a compelling mechanism, but a mechanism isn't proof of benefit for any particular condition.
What the Forzinity Approval Covers
From FDA's announcement and the prescribing information:
- Indication: to improve muscle strength in adults and children with Barth syndrome who weigh at least 30 kg
- Basis: accelerated approval, based on improved strength of the knee-extensor muscle (the one that straightens the leg). FDA considers that "reasonably likely to predict" real benefit, and continued approval may depend on a confirmatory trial.
- Form: a subcutaneous injection, given once daily under a prescription
- Most common side effects: injection-site reactions, mostly mild to moderate. FDA also noted serious reactions have been reported, and serious hypersensitivity to the ingredients is a contraindication.
It is not approved for aging, energy, athletic performance, heart failure or any other use.
Where Trials Have Struggled
SS-31 has been tested in other conditions, and the results are a useful reality check:
- Primary mitochondrial myopathy (MMPOWER-3): a 218-person randomized trial published in Neurology in 2023 did not meet its primary endpoints (6-minute walk distance and fatigue scores) after 24 weeks.
- Barth syndrome: evidence comes from the TAZPOWER program, including a long-term open-label extension published in 2024. That's the setting where FDA found enough to grant accelerated approval.
So the approval is real, but it's narrow, and SS-31 hasn't been shown to work broadly as a "mitochondria booster."
Research Vials vs Forzinity
Online "SS-31" vials are not Forzinity. FDA's August 2026 warning letters to peptide sellers listed "SS-31" and "SS-31 (Elamipretide)" among unapproved new drugs, even though the products were labeled "research use only." A prescription product comes with verified identity, sterility and labeling. A research vial doesn't.
For the regulatory backdrop, see counterfeit retatrutide and FDA warning letters, which covers the same "research use only" issue.
