Elamipretide started life as a lab curiosity. It came out of the Szeto-Schiller (SS) peptide series, a set of small peptides screened for mitochondrial targeting, where it was tagged SS-31. It has carried several names since: MTP-131, Bendavia, Ocuvia, and the development code under Stealth BioTherapeutics. Chemically it is a synthetic tetrapeptide, sequence D-Arg-Dmt-Lys-Phe-NH2, with two positive charges (D-arginine and lysine) that pull it toward the negatively charged inner mitochondrial membrane (Int. J. Mol. Sci. review, 2025).
On September 19, 2025 the FDA granted accelerated approval to elamipretide, branded FORZINITY, for Barth syndrome. That made it the first FDA-approved mitochondria-targeted drug, and the first treatment of any kind for that disease (Pharmacy Times; PubMed, 2025).
How it works
The drug binds cardiolipin, a phospholipid found almost exclusively in the inner mitochondrial membrane. Cardiolipin holds the folded membrane structures called cristae in shape and supports the electron transport chain that makes ATP. By binding and stabilizing cardiolipin, elamipretide is reported to preserve cristae integrity, cut reactive oxygen species, and help maintain membrane potential and ATP output (Int. J. Mol. Sci., 2025). It does this without meaningful opioid-receptor activity, despite the SS peptides emerging from opioid-peptide chemistry.
Barth syndrome is a fitting target because it is, at root, a disorder of cardiolipin metabolism. It is an ultra-rare, life-limiting genetic disease affecting roughly 150 people in the United States, mostly males.
What the trials show
The evidence is genuinely mixed, and the approval rested on a narrow endpoint.
- Barth syndrome (TAZPOWER). The randomized, placebo-controlled crossover portion of this trial did not meet its primary endpoints. Benefit showed up later: during the long open-label extension, knee extensor muscle strength improved by more than 45%, and that gain correlated with six-minute walk distance. The FDA used knee extensor strength as an intermediate clinical endpoint for accelerated approval (Genetics in Medicine, 2021; PubMed, 2025).
- Primary mitochondrial myopathy. An early dose-escalation study (SPIMM-201) hinted at a six-minute-walk benefit at the highest dose. The larger phase 3 MMPOWER-3 then provided Class I evidence that elamipretide did not improve the six-minute walk or fatigue at 24 weeks versus placebo (Neurology, MMPOWER-3).
- Other conditions. It has been studied in heart failure (PROGRESS-HF) and dry age-related macular degeneration (ReCLAIM), without an approval coming out of those programs.
So: a real, mechanistically grounded drug that cleared the bar for one ultra-rare disease on a surrogate measure, while failing its main endpoint in a larger muscle-disease trial. Accelerated approval means confirmatory evidence is still expected.
Approved use, route, and dose
FORZINITY is given as a subcutaneous injection; the Barth trials used 40 mg daily. The approved indication is adult and pediatric patients weighing at least 30 kg, to improve muscle strength (Pharmacy Times). Nothing here is dosing or medical advice; those decisions belong to a prescribing clinician.
Buyer and quality notes
Most elamipretide sold as "SS-31" by research-chemical vendors is not FORZINITY and is not a regulated pharmaceutical. It is marketed for research use only and is not approved for human consumption in that form. Because it is a four-residue peptide with D-amino acids and a modified tyrosine (Dmt), identity and purity are not things a buyer can eyeball. A real certificate of analysis with mass spec and HPLC, tied to the specific lot, is the only way to check that what is in the vial matches the label. peptideone aggregates third-party purity and identity testing where it exists; treat any vendor that cannot produce lot-level COAs with skepticism.
On anti-doping: elamipretide is not named on the WADA Prohibited List, but a non-approved performance-use peptide can still fall under WADA's catch-all S0 category for substances with no current regulatory approval for human use. Athletes should confirm status with their governing body rather than assume it is clear.