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October 16, 2026

FDA-Approved7/10 · Recommended

Elamipretide (SS-31): What the Science Really Says About the “Mitochondria Peptide”

In 2025, elamipretide became the first FDA-approved treatment for Barth syndrome, a rare inherited disease. Here’s how this mitochondria-targeting peptide works, what its trials in other conditions found, what’s known about safety, and why “SS-31” sold online isn’t the same as the approved drug.

Elamipretide: What the science really says about the "mitochondria peptide"

Elamipretide, also sold online as "SS-31," has a claim few peptides in our series can make: in 2025 it became an FDA-approved drug. It's the first treatment ever approved for Barth syndrome, a rare inherited disease. Here's how it works, what the trials found, and why that approval doesn't make it an anti-aging shot.

Peptide Advocate · Research explainer · Updated October 2026

What it isA small, four-amino-acid peptide that targets mitochondria, the cell's power plants1
Why people are excitedIt's the first FDA-approved treatment for Barth syndrome, approved in September 2025 as Forzinity2,4
Human evidenceSeveral placebo-controlled trials. Most missed their main goals, though some showed hopeful signals5–7
Legal statusPrescription drug for Barth syndrome only (accelerated approval). All other uses are investigational1,11

What is elamipretide?

Almost every cell runs on energy made by mitochondria. Inside each one, a folded inner membrane does the work, and a special fat called cardiolipin helps hold those folds in shape. Elamipretide is a tiny peptide, just four amino acids, that travels to that inner membrane and binds cardiolipin, improving how mitochondria are built and how well they work.1

How elamipretide works Mitochondria have folded inner membranes, held in shape partly by a fat called cardiolipin. In Barth syndrome, cardiolipin is faulty and the folds become disorganized, so cells make less energy. Elamipretide binds cardiolipin on the inner membrane and helps restore mitochondrial structure and function. Shoring up the cell's power plants Mitochondria make energy along folded inner membranes held in shape partly by cardiolipin Faulty cardiolipin Folds lose their shape, less energy (as in Barth syndrome) With elamipretide Binds cardiolipin on the inner membrane, improving structure and function = elamipretide (4 amino acids). Simplified illustration, not to scale.
Based on the mechanism described in the FDA-approved label and MedlinePlus.1,3 Illustration: Peptide Advocate.

That's why its first approval is for Barth syndrome. The disease is caused by changes in the TAFAZZIN gene, which leave cells without enough working cardiolipin. It almost always affects boys and men, and it weakens the heart and muscles, lowers infection-fighting white blood cells, and causes fatigue. It affects an estimated 1 in 300,000 to 400,000 people worldwide.3

Why researchers are excited

Mitochondrial problems show up in many conditions, from rare genetic diseases to heart failure and age-related eye disease. A drug that steadies mitochondria from the inside could, in theory, help many of them. That's why elamipretide has been tested in a range of conditions, and why its developer, now called Mighty Therapeutics, is still running trials in dry age-related macular degeneration and other diseases.9,10

The Barth syndrome approval was a milestone. Before September 19, 2025, families had no FDA-approved treatment at all for the disease, which affects about 150 people in the U.S.2,4

What about people?

Elamipretide has been studied more rigorously than most peptides, in randomized, placebo-controlled trials. The honest summary: the big trials mostly missed their main goals, but several showed signals that kept researchers going.

ConditionTrialWhat happenedTakeaway
Barth syndrome
TAZPOWER		12 patients, placebo-controlled crossover, then open-labelNot better than placebo on walking distance or fatigue at first. In the long open-label phase, leg muscle strength rose (median +63 newtons by week 168 in 8 patients)1Strength gains were the basis for accelerated approval
Primary mitochondrial myopathy
MMPOWER-3, 2023		218 adults, 24 weeksNo improvement in walking distance or fatigue vs. placebo5A possible benefit in one genetic subgroup needs confirming
Dry macular degeneration
ReCLAIM-2, 2025		176 adults, 48 weeksMissed its main vision and lesion-growth goals, but slowed loss of a key retina layer by about 43%6A larger phase 3 trial is now under way
Heart failure
PROGRESS-HF, 2020		71 adults, 4 weeksNo improvement in heart pumping vs. placebo7Well tolerated, but no benefit seen

About that retina result: the "43% slower" finding was a secondary, exploratory measure, so it suggests a benefit rather than proving one. The company's phase 3 ReNEW trial uses that measure as its main goal and is expected to finish in late 2027.6,10

Sept. 19, 2025FDA grants accelerated approval for Barth syndrome2
~150people in the U.S. with Barth syndrome4
218adults in the largest trial, which missed its goals5
2029expected completion of the required confirmatory trial2

Is elamipretide safe?

Because it's an approved drug, elamipretide has an FDA-reviewed safety label, which is more than most peptides have. The main issue is the skin where it's injected each day.1,5

Side effects in the largest elamipretide trial In a 24-week trial of 218 adults, injection site redness occurred in 86.2% on elamipretide vs 28.4% on placebo; itching 75.2% vs 9.2%; any side effect 98.2% vs 76.1%; serious side effects 4.6% vs 2.8%, none judged drug-related; stopping due to side effects 7.3% vs 1.8%. Mostly a skin story Share of patients with each effect, MMPOWER-3 trial (218 adults, 24 weeks) Elamipretide Placebo Redness at injection site 86.2% 28.4% Itching at injection site 75.2% 9.2% Any side effect 98.2% 76.1% Serious side effect 4.6% 2.8% Stopped due to side effects 7.3% 1.8% None of the serious side effects were judged to be caused by the drug.
Source: Karaa et al., Neurology, 2023.5
  • Injection-site reactions are very common: redness, pain, itching, firmness, bruising and hives.1
  • Allergic reactions. Serious allergic reactions needing emergency care have occurred. Anyone who has one shouldn't take it again.1
  • Not for newborns. The product contains benzyl alcohol, which can be dangerous for premature and low-birth-weight babies.1
  • Blood counts. Levels of eosinophils, a type of white blood cell, rose with longer use, without related symptoms.1
  • Ongoing studies. The FDA still requires long-term animal cancer studies and a drug-interaction study, which is standard for a newly approved drug.2
"SS-31" online is not Forzinity. Research-chemical SS-31 sold online isn't approved for human use, and its identity, purity and sterility are uncertain. The FDA's approval applies only to the prescription product, for Barth syndrome.11,12

Athletes: Elamipretide is approved only for a rare disease, and its status under anti-doping rules isn't clear-cut. Check with your anti-doping authority or Global DRO, and get a therapeutic use exemption if you need it medically.11

Where elamipretide stands with the FDA

Elamipretide took a long and bumpy road to approval, and it isn't fully finished. It received accelerated approval, which lets the FDA approve a drug for a serious disease based on an early measure, here leg muscle strength, that's expected to predict real benefit. The company must now prove that benefit in a new trial, or the approval can be withdrawn.2

How elamipretide's status has changed

  1. 2019FDA declines to accept the first application for Barth syndrome, asking for stronger data8
  2. 2019–2023MMPOWER-3 trial in primary mitochondrial myopathy misses its goals; results published in 20235
  3. 2024FDA advisory committee votes 10–6 that elamipretide is effective for Barth syndrome8
  4. May 2025FDA rejects the application despite the vote, but opens a path based on muscle strength8
  5. September 19, 2025FDA grants accelerated approval as Forzinity for Barth syndrome patients weighing at least 30 kg (66 lb)2
  6. 2026Launch under way; company renamed Mighty Therapeutics; plans to study younger children9,10
  7. NextConfirmatory trial due to finish in 2029; dry macular degeneration phase 3 results expected after late 20272,10

What this means for everyone else: The approval covers only Barth syndrome. Using elamipretide for energy, aging or anything else is off-label or investigational, and products sold as "SS-31" outside prescription channels aren't the approved drug.11

If you're curious about elamipretide

  • If you or your child has Barth syndrome, ask your care team whether Forzinity is right for you.
  • For other mitochondrial diseases, ask a specialist about clinical trials. That's the safe way to get access to investigational drugs.
  • Worried about vision loss? See an eye doctor. There are FDA-approved treatments for some forms of macular degeneration.
  • Skip "research use only" SS-31. It isn't the approved product, and quality is unknown.
  • Tell your doctor about any peptides or supplements you take.

The bottom line

Elamipretide is a genuine success story for families living with Barth syndrome: a rare disease that went from no approved treatment to one. Its science is elegant, targeting the very structure that keeps mitochondria working. But its record outside Barth syndrome is sobering, with large trials in muscle disease and heart failure finding no benefit, and its eye-disease results still awaiting confirmation. Even its approval is provisional until a confirmatory trial is done. Elamipretide is real medicine for people with one rare disease and a promising research tool for others, but it isn't a proven anti-aging shot.

References

  1. Stealth BioTherapeutics. Forzinity (elamipretide) injection: prescribing information; revised September 2025. drugs.com
  2. U.S. Food and Drug Administration. NDA 215244 approval letter, Forzinity (elamipretide); September 19, 2025. fda.gov
  3. MedlinePlus Genetics. Barth syndrome. U.S. National Library of Medicine. medlineplus.gov
  4. Epocrates. FDA OKs first treatment for Barth syndrome; 2025. epocrates.com
  5. 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. doi.org
  6. Ehlers JP, Hu A, Boyer D, 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. 2025;5(1):100628. doaj.org
  7. 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. henryford.com
  8. Pharmaphorum. Axe falls on Stealth Bio staff after FDA rejects lead drug; May 30, 2025. pharmaphorum.com
  9. Stealth BioTherapeutics. Commercial launch update and pipeline progress across mitochondrial disease portfolio; April 30, 2026. biospace.com
  10. Mighty Therapeutics. Mighty Therapeutics, formerly Stealth BioTherapeutics, announces new name; June 16, 2026. biospace.com
  11. Outliyr. SS-31 (elamipretide) report; updated September 2026. outliyr.com
  12. Rite Aid. SS-31 (elamipretide): status and safety; updated September 29, 2026. riteaid.com

This article is for general education and is not medical advice. Elamipretide (Forzinity) is FDA-approved only to improve muscle strength in people with Barth syndrome who weigh at least 30 kg, under accelerated approval. This article does not recommend using it for any other purpose and does not provide dosing information. Talk with a licensed healthcare provider before starting any new treatment. Regulatory information is current as of October 16, 2026 and is changing quickly. Charts and illustrations are original works by Peptide Advocate.

Peptides Referenced

SS-31 (Elamipretide)

Mitochondrial Peptide

Targets cardiolipin in the inner mitochondrial membrane to improve energy production and reduce oxidative stress.