Skip to content
Educational information only. Not medical advice. We sell nothing and take no affiliate money.
By /
Peptide (FDA approved drug)Limited humanFDA approved

SS-31 (elamipretide)

Elamipretide

Last reviewed October 27, 2026 · 19 sources · Written for general readers · Compare with another compound →

The bottom line

SS-31, now called elamipretide, became the first FDA approved treatment for Barth syndrome in September 2025, sold as Forzinity. The approval is an accelerated one based on muscle strength in a very small group, and a confirmatory trial is under way. Larger trials in mitochondrial muscle disease, heart attack and eye disease missed their main goals, nearly everyone on it gets injection site reactions, and it has never been shown to slow aging.

Where the evidence stands

What it is

Elamipretide, first known as SS-31 and in some trials as MTP-131 or Bendavia, is a small peptide of four amino acids. It sticks to cardiolipin, a fat in the inner membrane of mitochondria, the cell’s power plants.[1][2][3]

In September 2025 FDA gave it accelerated approval under the brand name Forzinity for Barth syndrome, a rare, life threatening inherited mitochondrial disease, in patients weighing at least 30 kg.[4][2] Online sellers also market “SS-31” for aging and energy, which is not an approved use.

Name
SS-31 (elamipretide) (Elamipretide)
Other names
SS-31, Forzinity, MTP-131, Bendavia
Type
Peptide (FDA approved drug)
Sequence
D-Arg-Dmt-Lys-Phe-NH2 (Dmt is 2,6-dimethyltyrosine)
CAS number
736992-21-5
Formula
C32H49N9O5
Molecular weight
About 639.8 g/mol

What it does in the body

Elamipretide (SS-31) is a lab made peptide of four amino acids; it does not occur in the body. FDA's label describes it as a cardiolipin binder: it settles in the inner membrane of mitochondria, where energy is made, and improves mitochondrial shape and function.[2] Cardiolipin is a fat that holds the energy making machinery together, and the drug is designed to protect it.[5]

This is the biology, area by area. A change measured in the body, like a higher blood level, does not always mean a person feels a benefit. The claims check below covers that.

Energy and cells

Well established

The FDA label states that elamipretide binds cardiolipin in the inner mitochondrial membrane and improves mitochondrial structure and function.[2] In lab and animal work it helped keep the electron transport chain working and lowered harmful oxygen byproducts.[5][6]

Muscle and strength

Measured in people

In 39 healthy adults aged 60 to 85 with weaker mitochondria, a single two hour IV infusion raised the hand muscle's maximum ATP production by 27 percent versus 12 percent on placebo right after the drip. The effect was gone by day 7, and fatigue resistance, a secondary muscle test, did not clearly improve.[8] The effect was gone by day 7, and fatigue resistance, the main muscle test, did not clearly improve.[8] In Barth syndrome, knee muscle strength did not rise in the 12 week placebo phase, but median strength rose 63 newtons by week 168 in the open extension.[2]

Heart

Measured in people

In 36 people with weak hearts, one IV infusion slightly shrank heart chamber volumes at the end of the drip.[7] But in 71 patients given daily shots for four weeks, heart chamber size and pumping did not change versus placebo, and in heart attack patients an IV infusion did not reduce heart damage.[9][3] In 24 month old mice, eight weeks of SS-31 reversed age related stiffening of the heart, and about half the gain was lost four weeks after stopping.[10]

Eyes

Measured in people

In 176 people with dry macular degeneration, 48 weeks of daily shots did not slow vision loss in dim light or the growth of damaged areas, the main goals.[11] Eye drops in 12 people with an inherited optic nerve disease did not improve sharpness of vision.[12]

Immune system and blood

Measured in people

Eosinophils, a type of white blood cell involved in allergies, often rose with use of 30 days or more, peaking around day 90 and returning to normal later.[2] Serious allergic reactions needing emergency care have been reported.[2]

Kidneys and clearance

Well established

After a shot under the skin, blood levels peak within half an hour to an hour, and about 92 percent of the drug is absorbed. Elamipretide and its breakdown products leave the body in urine, nearly all within 48 hours.[2] After an IV drip it was undetectable in blood by 24 hours.[7]

How it works

SS-31 is designed to protect mitochondria from the inside.

  • It binds cardiolipin and is reported to keep the energy making machinery in mitochondria working properly.[2][5]
  • Lab and animal work suggests it helps preserve mitochondrial structure and energy output and lowers harmful oxygen byproducts.[5][6]
  • Given by IV, it peaks in the blood at the end of the drip and is undetectable by 24 hours.[7]

The mechanism is well studied in the lab, but how much it explains benefit in patients is less certain.

What the research shows

We keep animal and human evidence apart. A result in animals is a reason to study something in people, not proof that it works in people.

Animal and lab studies

Broad benefits in animal models

  • Reviews by the peptide’s inventor report extensive animal studies showing benefit in diseases where cells run short of energy.[5]
  • Researchers also report that these peptides restored mitochondrial function and organ function in aging animals.[6]
  • Lab and animal studies suggest it lowers harmful oxygen byproducts and helps keep mitochondrial structure intact.[5]
  • In 24 month old mice, eight weeks of SS-31 from a small pump under the skin reversed age related heart stiffening, lowered harmful oxygen byproducts and improved treadmill running; about half the heart benefit faded four weeks after stopping.[10]

Limit: These reviews come from the inventor, and aging benefits in animals have not been shown in people.

Human studies

Approved for one rare disease on small data; most larger trials missed

  • Barth syndrome trial: 12 males aged 12 and up took daily shots under the skin and placebo in turn for 12 weeks each. It did not beat placebo on walking distance or fatigue, the main goals, and strength did not rise.[2][15]
  • Barth extension: 10 patients entered an open extension and 8 stayed to week 168. Median knee strength rose 63 newtons and walking distance improved, but without a placebo group these gains are harder to interpret.[2][15]
  • Approval: FDA based its accelerated approval on knee muscle strength and requires a placebo controlled trial to confirm real benefit.[4] That trial began in July 2026.[16]
  • Mitochondrial muscle disease, short trial: 36 adults got IV infusions for five days. The highest group walked 64.5 meters farther in six minutes versus 20.4 meters on placebo, and other measures did not change.[14]
  • Mitochondrial muscle disease, large trial: 218 adults took daily shots or placebo for 24 weeks. Walking distance rose 14.1 meters on the drug and 17.3 meters on placebo, and fatigue scores did not differ.[13]
  • After the fact analysis of that trial suggested people with certain nuclear gene defects walked farther, which led to a new trial, but this was not a planned main result.[13][17]
  • Nuclear gene mitochondrial disease: a 48 week placebo controlled phase 3 trial of daily shots in 102 people, called NuPower, was completed in 2024. We found no published results.[18]
  • Muscle energy in older adults: 39 healthy adults aged 60 to 85 got one two hour IV infusion or placebo. Maximum ATP production in a hand muscle rose 27 percent versus 12 percent on placebo right after the drip, but not one week later, and the main fatigue test did not improve.[8]
  • Heart attack: in the EMBRACE STEMI trial, an IV infusion during artery opening did not lower heart damage markers or improve imaging results versus placebo.[3]
  • Heart failure: in 36 patients, a single IV infusion was well tolerated, and the highest amount tested reduced heart chamber volumes by 14 to 18 milliliters at the end of the drip versus placebo.[7]
  • Heart failure, four weeks: in the PROGRESS-HF trial, 71 adults with weak hearts got daily shots of one of two amounts or placebo for 28 days. Heart chamber size on MRI did not improve with either amount, and side effects were similar across groups.[9]
  • Dry macular degeneration: in 176 adults over 48 weeks, daily shots missed both main goals. Side effects occurred in 86 percent on the drug and 71 percent on placebo, mostly injection site reactions.[11]
  • Inherited optic nerve disease: eye drops in 12 patients over 52 weeks were well tolerated but did not improve sharpness of vision versus placebo drops.[12]

Limit: Benefit rests on a tiny trial plus an uncontrolled extension, larger trials mostly missed their goals, and no trial tests it for aging in healthy people.

Claims check

The most common claims about this compound, and what studies actually found. Verdicts rate the evidence, not whether you should use it.

Slows aging and recharges mitochondria in healthy people

Only in animals

Researchers report that these peptides restored mitochondrial and organ function in aging animals, and in old mice eight weeks of SS-31 reversed age related heart stiffening.[6][10] In people, one IV dose briefly raised muscle energy production in older adults, but no trial has tested whether it slows aging, and its other human trials were in people with specific diseases.[8][2][13]

Improves muscle strength and endurance

Mixed results

In a five day trial of 36 adults with mitochondrial muscle disease, those on the highest IV amount walked 64.5 meters farther in six minutes versus 20.4 meters on placebo, a borderline result.[14] But the larger 24 week trial of 218 people found no difference in walking distance.[13] In Barth syndrome, strength did not improve over 12 weeks versus placebo and rose only in a later uncontrolled extension.[2]

Fights fatigue

No benefit in trials so far

In the 218 person mitochondrial muscle disease trial, fatigue scores improved about the same on elamipretide and placebo over 24 weeks.[13] In the 12 person Barth syndrome trial, fatigue was not better than on placebo.[2]

Treats Barth syndrome

Mixed results

In a crossover trial of 12 patients, it did not beat placebo on walking distance or fatigue over 12 weeks. In an open extension, median knee muscle strength rose by 63 newtons after about three years in 8 patients.[2][13][15] FDA granted accelerated approval on that strength measure and requires a confirmatory trial, which began in July 2026.[4][16]

Protects the heart

Mixed results

In heart attack patients getting an artery opened, an IV infusion did not reduce heart muscle damage markers or improve imaging or clinical results versus placebo.[3] In 36 people with weak hearts, a single four hour IV infusion slightly shrank heart chamber volumes at the highest amount, but this was measured only at the end of the drip.[7] In 71 patients with weak hearts, four weeks of daily shots did not change heart chamber size versus placebo.[9]

Protects eyesight in macular degeneration

Mixed results

In 176 people with dry age related macular degeneration, 48 weeks of daily shots missed both main goals, vision in low light and growth of damaged areas. Some secondary measures looked better, such as 14.6 percent gaining two lines of low light vision versus 2.1 percent on placebo.[11] Eye drops in 12 people with an inherited optic nerve disease also missed their main vision goal.[12]

Boosts energy production in aging muscle

Mixed results

In a placebo controlled trial of 39 adults aged 60 to 85, one IV infusion raised maximum ATP production in a hand muscle by 27 percent versus 12 percent on placebo right after the drip, a borderline result. By day 7 the difference was gone, and the planned fatigue test did not improve; the authors called the study underpowered.[8] By day 7 the difference was gone, and the main fatigue test did not improve; the authors called the study underpowered.[8]

Known risks and side effects

  • Injection site reactions. In the Barth syndrome trial, every patient on the drug had a reaction where the shot went in, compared with 67 percent on placebo. Redness occurred in 100 percent versus 25 percent, pain in 75 versus 42 percent, and hardening and itching in 67 versus 17 percent.[2]
  • More people stop because of side effects. In the 218 person trial, 98 percent on the drug reported a side effect versus 76 percent on placebo, and 7.3 percent stopped because of side effects versus 1.8 percent. Serious events were uncommon and judged unrelated.[13]
  • Serious allergic reactions. The label warns of serious allergic reactions that needed emergency care, including rash, skin lesions and cough, which can appear minutes to months after starting.[2]
  • Blood count changes. Eosinophils, a type of white blood cell, often rose in studies of 30 days or longer, peaking around day 90 and later returning to normal, with no symptoms linked to the rise.[2]
  • Unregulated research peptide. “SS-31” sold online for aging is not the FDA approved product and has no checks on purity, sterility or strength. The approved drug is labeled only for Barth syndrome.[2]

Regulatory status

Today: Elamipretide is FDA approved as Forzinity, under accelerated approval, only for Barth syndrome in patients weighing at least 30 kg. Continued approval depends on a confirmatory trial.[4][2]

  1. A large phase 3 trial in primary mitochondrial myopathy is published showing no benefit over placebo.[13]
  2. FDA issues a complete response letter declining approval for Barth syndrome, even though an advisory committee had voted 10 to 6 that the drug was effective.[19]
  3. FDA grants accelerated approval to Forzinity as the first treatment for Barth syndrome.[4]
  4. The first patient is dosed in the required confirmatory trial in Barth syndrome.[16]

Sources

  1. U.S. FDA Global Substance Registration System. Elamipretide (UNII 87GWG91S09). FDA GSRS
  2. FORZINITY (elamipretide hydrochloride) injection. Prescribing information. DailyMed, U.S. National Library of Medicine. Revised December 2025. DailyMed
  3. Gibson CM, Giugliano RP, Kloner RA, et al. EMBRACE STEMI study: a Phase 2a trial to evaluate the safety, tolerability, and efficacy of intravenous MTP-131 on reperfusion injury in patients undergoing primary percutaneous coronary intervention. Eur Heart J. 2016;37(16):1296-1303. PMID 26586786
  4. U.S. Food and Drug Administration. FDA Grants Accelerated Approval to First Treatment for Barth Syndrome. September 19, 2025. FDA
  5. Szeto HH. First-in-class cardiolipin-protective compound as a therapeutic agent to restore mitochondrial bioenergetics. Br J Pharmacol. 2014;171(8):2029-50. PMID 24117165
  6. Szeto HH, Liu S. Cardiolipin-targeted peptides rejuvenate mitochondrial function, remodel mitochondria, and promote tissue regeneration during aging. Arch Biochem Biophys. 2018;660:137-148. PMID 30359579
  7. Daubert MA, Yow E, Dunn G, et al. Novel Mitochondria-Targeting Peptide in Heart Failure Treatment: A Randomized, Placebo-Controlled Trial of Elamipretide. Circ Heart Fail. 2017;10(12):e004389. PMID 29217757
  8. Roshanravan B, Liu SZ, Ali AS, et al. In vivo mitochondrial ATP production is improved in older adult skeletal muscle after a single dose of elamipretide in a randomized trial. PLoS One. 2021;16(7):e0253849. DOI 10.1371/journal.pone.0253849
  9. Butler J, Khan MS, Anker SD, et al. 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. 2020. PMID 32068002
  10. Chiao YA, Zhang H, Sweetwyne M, et al. Late-life restoration of mitochondrial function reverses cardiac dysfunction in old mice. eLife. 2020;9:e55513. DOI 10.7554/eLife.55513
  11. Ehlers JP, Hu AYH, Boyer DS, et al. 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. 2024;5(1):100628. PMID 39605874
  12. Karanjia R, Sadun AA. Elamipretide Topical Ophthalmic Solution for the Treatment of Subjects with Leber Hereditary Optic Neuropathy: A Randomized Trial. Ophthalmology. 2024;131(4):422-433. PMID 37923251
  13. Karaa A, Bertini E, Carelli V, et al. Efficacy and Safety of Elamipretide in Individuals With Primary Mitochondrial Myopathy: The MMPOWER-3 Randomized Clinical Trial. Neurology. 2023;101(3):e238-e252. PMID 37268435
  14. Karaa A, Haas R, Goldstein A, et al. Randomized dose-escalation trial of elamipretide in adults with primary mitochondrial myopathy. Neurology. 2018;90(14):e1212-e1221. PMID 29500292
  15. Thompson WR, Manuel R, Abbruscato A, et al. Long-term efficacy and safety of elamipretide in patients with Barth syndrome: 168-week open-label extension results of TAZPOWER. Genet Med. 2024;26(7):101138. PMID 38602181
  16. Mighty Therapeutics. Mighty Therapeutics Announces First Patient Dosed in Phase 4 Confirmatory Study of Elamipretide in Barth Syndrome. Press release via BioSpace, July 8, 2026. Company press release
  17. Karaa A, Bertini E, Carelli V, et al. Genotype-specific effects of elamipretide in patients with primary mitochondrial myopathy: a post hoc analysis of the MMPOWER-3 trial. Orphanet J Rare Dis. 2024;19(1):431. PMID 39574155
  18. ClinicalTrials.gov. Study to Evaluate Efficacy and Safety of Elamipretide in Subjects With Primary Mitochondrial Disease From Nuclear DNA Mutations (nPMD) (NuPower). NCT05162768. NCT05162768
  19. Pharmaceutical Technology. FDA rejects Stealth Bio's Barth syndrome treatment after 16.5-month review. May 30, 2025. Trade news
Medical disclaimer

This page is educational information only. It is not medical advice and does not replace care from a licensed medical provider. Do not use this page to decide whether to take any substance. Talk to a licensed medical provider first.

Found an error or a newer study? We correct pages fast.

Report a correction →
Scroll to Top