SS-31 became a drug: what elamipretide's approval means and doesn't

What was approved

Elamipretide High, long known in research as SS-31, binds cardiolipin, a lipid of the inner mitochondrial membrane; the foundational studies showed this binding in mitochondria ¹. On September 19, 2025 the FDA approved it under priority review as Forzinity, from Stealth BioTherapeutics ². The label's indication is precise: to improve muscle strength in adult and paediatric patients with Barth syndrome who weigh at least 30 kg ³. The dose is 40 mg injected under the skin once a day, reduced in adults with severe kidney impairment ³. The label's warnings are benzyl-alcohol toxicity in newborns, from an ingredient of the formulation, and hypersensitivity reactions ³.

It is the first approved drug described as targeting mitochondria, according to our entry ⁴. As of October 2, 2026, Drugs@FDA lists it as a prescription product ².

Why "accelerated" matters

Accelerated approval lets the FDA approve a drug for a serious condition on an intermediate end point that is reasonably likely to predict real benefit. Forzinity's label says its approval was based on an improvement in knee-extensor muscle strength, an intermediate clinical end point, and that continued approval may depend on a confirmatory trial verifying clinical benefit ³.

The evidence behind it is small, as it often is in ultra-rare diseases. TAZPOWER randomised 12 people with Barth syndrome to 12 weeks of elamipretide or placebo and then swapped them; the crossover did not meet its primary end point ⁵. In the open-label extension, 10 patients continued on 40 mg daily and 8 reached 168 weeks, with sustained improvements in walking distance, muscle strength and fatigue scores ⁶. A comparison of 8 treated patients with 19 untreated patients from a natural-history study found a 79.7-metre advantage in six-minute walk distance at week 64 ⁷. Comparisons with external controls are weaker than randomised trials, which is part of why the approval came with conditions.

Where SS-31 did not work

The same molecule has been tested in larger populations, and the results are the reason the approval should not be read broadly. In MMPOWER-3, the largest elamipretide trial, 218 adults with genetically confirmed primary mitochondrial myopathy received 40 mg daily or placebo for 24 weeks; it did not improve the six-minute walk test or fatigue scores ⁸. In PROGRESS-HF, 71 people with heart failure and reduced ejection fraction received 4 or 40 mg daily or placebo for 28 days; the primary heart-imaging end point did not differ between groups ⁹. In ReCLAIM-2, a 48-week trial in dry age-related macular degeneration, the primary vision and lesion-size end points were not met, although a secondary measure of photoreceptor integrity favoured the drug, and injection-site reactions led 17% to stop ¹⁰.

A review written after approval summarises the whole programme, including these negative readouts ¹¹. The pattern is common in drug development: a molecule can help a small group with a specific disease and do nothing measurable in broader conditions that share a mechanism on paper.

What the approval does not mean

Gray-market sellers have marketed SS-31 for energy, ageing, endurance and recovery. The approval supports none of those uses. It covers one formulation, one dose and one rare disease, on the strength of a muscle-strength measure; the trials in common conditions that people might hope to treat missed their main goals ^{8 9 10}. A vial labelled SS-31 from a research-chemical site is also not Forzinity: it has none of the approved product's manufacturing controls, and its contents are whatever the supplier put in it.

For sport, SS-31 is not named on WADA's 2026 or 2027 Prohibited List, and as an approved drug it is not caught by S0, according to our entry's review of the List ⁴. That is a statement about doping rules, not about safety or benefit.

Frequently asked questions

Is SS-31 FDA-approved?

Yes, as elamipretide (Forzinity), under accelerated approval on September 19, 2025, to improve muscle strength in people with Barth syndrome weighing at least 30 kg. That is its only approved use.

Does the approval mean SS-31 works for anti-ageing or energy?

No. It covers one rare disease. Trials in primary mitochondrial myopathy, heart failure and dry macular degeneration missed their primary end points.

What is the approved dose of elamipretide?

40 mg injected under the skin once daily for patients weighing at least 30 kg, reduced in adults with severe kidney impairment, according to the Forzinity label.

Is research-grade SS-31 the same as Forzinity?

No. Products sold as research chemicals are not the approved drug and have none of its manufacturing or quality controls.

Related on Grey Peptides

• SS-31 (elamipretide)
• MOTS-c
• MOTS-c: from exercise-mimetic science to the FDA

Sources

1. Birk, A. V., et al. (2013). The mitochondrial-targeted compound SS-31 re-energizes ischemic mitochondria by interacting with cardiolipin. J Am Soc Nephrol, 24(8), 1250-61. PMID: 23813215
2. US FDA, Drugs@FDA (openFDA): FORZINITY, NDA 215244, original approval September 19, 2025, priority review; prescription. Read October 2, 2026.
3. Stealth BioTherapeutics. FORZINITY (elamipretide hydrochloride) injection US prescribing information (DailyMed set 146bf34c-76f2-48db-ac07-fb29cce2cd75, effective December 10, 2025); read October 2, 2026.
4. Grey Peptides dataset, ss-31 record (approval details and WADA 2026 and 2027 review); read October 2, 2026.
5. Reid Thompson, W., et al. (2021). A phase 2/3 randomized clinical trial followed by an open-label extension to evaluate the effectiveness of elamipretide in Barth syndrome, a genetic disorder of mitochondrial cardiolipin metabolism. Genet Med, 23(3), 471-478. PMID: 33077895
6. Thompson, W. R., et al. (2024). Long-term efficacy and safety of elamipretide in patients with Barth syndrome: 168-week open-label extension results of TAZPOWER. Genet Med, 26(7), 101138. PMID: 38602181
7. Hornby, B., et al. (2022). Natural history comparison study to assess the efficacy of elamipretide in patients with Barth syndrome. Orphanet J Rare Dis, 17(1), 336. PMID: 36056411
8. Karaa, A., et al. (2023). Efficacy and Safety of Elamipretide in Individuals With Primary Mitochondrial Myopathy: The MMPOWER-3 Randomized Clinical Trial. Neurology, 101(3), e238-e252. PMID: 37268435
9. Butler, J., et al. (2020). Effects of Elamipretide on Left Ventricular Function in Patients With Heart Failure With Reduced Ejection Fraction: The PROGRESS-HF Phase 2 Trial. J Card Fail, 26(5), 429-437. PMID: 32068002
10. Ehlers, J. P., et al. (2025). ReCLAIM-2: A Randomized Phase II Clinical Trial Evaluating Elamipretide in Age-related Macular Degeneration, Geographic Atrophy Growth, Visual Function, and Ellipsoid Zone Preservation. Ophthalmol Sci, 5(1), 100628. PMID: 39605874
11. Shirley, M. (2026). Elamipretide: First Approval. Drugs, 86(3), 377-383. PMID: 41335372

Educational information, not medical advice. Each dose in this guide names its source, an approved label or a published study. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose.