Elamipretide: evidence, FDA status and research

It is a drug for Barth syndrome, a rare inherited illness that weakens muscles. It was approved on thin evidence: a 12-person trial missed its main goals.

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Elamipretide is talked about as a mitochondria-targeting peptide for energy, aging and muscle, and as the first drug for Barth syndrome.

Studies say

A tiny crossover trial plus open-label follow-up earned a conditional approval in Barth syndrome, while the one large randomized trial in mitochondrial myopathy was negative, which lands at B for the approved use and lower for everything else.

Why grade B. The Barth syndrome approval is based on TAZPOWER, a 12-patient randomized crossover trial that missed its primary endpoints, followed by a 168-week open-label extension in which walking distance and strength improved against the natural history of the disease. ¹² The largest trial of elamipretide, MMPOWER-3 in 218 people with primary mitochondrial myopathy, failed both primary endpoints, so for the broader mitochondrial-health claims found online the evidence is negative. ⁴

FDA. Approved under the accelerated pathway. On September 19, 2025 the FDA approved elamipretide as Forzinity (Stealth BioTherapeutics) to improve muscle strength in adults and children weighing at least 30 kg who have Barth syndrome, a rare mitochondrial disease. The approval rests on a surrogate measure, knee extensor strength, and a confirmatory trial is required. It is not approved for any other condition.

Written from 4 cited sources. Fact-checked 2026-10-27: 16 claims checked, 3 corrected. Last refreshed 2026-10-27. Not physician reviewed.

What this means for you

What people take it for: Muscle weakness in Barth syndrome, and energy or aging
Can a US doctor prescribe it?: Yes, FDA approved for muscle strength in Barth syndrome, on a conditional basis.
Properly tested in people?: Partly: some human trials, with gaps. The approval rests on a trial of 12 people.

Evidence checklist

Randomised controlled trial TAZPOWER crossover; MMPOWER-3 placebo-controlledyes
Human study over 100 people TAZPOWER 12 patients; MMPOWER-3 218, negativeno
More than one research group Article does not say who ran the trialsno information
Clinical outcomes, not surrogate markers Surrogate: knee extensor strengthno
Human safety data beyond case reports Few hundred people; injection-site reactions commonyes

Drawn from the cited studies below. A dash means the sources give no information.

What it is

Elamipretide (formerly SS-31 or Bendavia) is a lab-made peptide of four amino acids. It builds up in the inner membrane of mitochondria. These are the parts of a cell that make most of its energy. Stealth BioTherapeutics developed it. Researchers tested it in heart failure, eye disease and several mitochondrial disorders. That took more than a decade before its first approval. ¹²

Barth syndrome is an X-linked disorder of the gene TAZ. The gene affects the remodeling of cardiolipin, a fat found only in the mitochondrial membrane. The disease causes weak heart muscle and weak skeletal muscle. It also causes low neutrophil counts and slow growth. A few hundred people worldwide have it. Forzinity is the first approved treatment. ¹²

How it works

Elamipretide binds cardiolipin in the inner mitochondrial membrane. Cardiolipin anchors the protein complexes of the respiratory chain. When it is abnormal, as in Barth syndrome, those complexes work less well. They also leak more reactive oxygen species. The peptide is thought to steady cardiolipin's structure and the membrane's curve. That would improve energy production and cut oxidative damage. Cell and animal studies worked out most of this mechanism. The trials measured function instead, such as walking distance and strength. ¹

What human research shows

TAZPOWER enrolled 12 patients aged 12 and older with genetically confirmed Barth syndrome. It was a double-blind crossover design. Patients took elamipretide for 12 weeks and placebo for 12 weeks, with a washout between. The blinded phase showed no significant differences on its main measures. These were the six-minute walk test and a fatigue questionnaire. Ten patients then entered a 168-week open-label extension. Eight completed it. They increased their six-minute walk distance by an average of 96 meters from baseline. Knee extensor strength rose over the same period. ¹

The FDA first declined the application in May 2025 because the controlled phase was negative. Stealth refiled under the accelerated approval pathway. It used knee extensor strength as a surrogate measure reasonably likely to predict benefit. The agency approved on that basis in September 2025. It required a post-approval randomized trial to confirm clinical benefit. ²

Outside Barth syndrome the record is weaker. MMPOWER-3 randomized 218 adults with primary mitochondrial myopathy. They got elamipretide or placebo for 24 weeks. The trial found no significant difference in six-minute walk distance or fatigue. Those were its two main measures. ⁴

Study	Model	Finding
TAZPOWER and 168-week extension	Humans, n=12 randomized crossover, then 10 in open-label extension	The blinded phase missed its primary endpoints; completers of the extension walked 96 meters farther than at baseline and gained knee strength. ¹
Forzinity prescribing information	FDA label, accelerated approval 2025	Approved to improve muscle strength in Barth syndrome based on knee extensor strength, with a confirmatory trial required. ²
MMPOWER-3	Humans, n=218, randomized double-blind placebo-controlled, 24 weeks, primary mitochondrial myopathy	No difference from placebo in six-minute walk distance or fatigue score. ⁴

Safety

Injection-site reactions are the main side effect. They include pain, itching, redness and hardening. On the label, all 12 TAZPOWER patients had a local reaction while on elamipretide. These were also the commonest adverse events in the open-label extension. The label also notes a temporary rise in eosinophils, a type of white blood cell. In MMPOWER-3 the drug was described as well tolerated. Most adverse events were mild to moderate. Only a few hundred people in total have used it. So rare effects cannot be ruled out. ¹²⁴

Questions for your clinician

What confirmatory trial is under way for the Barth syndrome approval?
What does the failed mitochondrial myopathy trial say about other uses?
How are injection-site reactions handled over long use?

Questions people ask

Is elamipretide FDA-approved?

Yes, for one use. Forzinity received accelerated approval in September 2025. It is approved to improve muscle strength in people with Barth syndrome who weigh at least 30 kg. The approval depends on a confirmatory trial. ²

Does elamipretide work for general mitochondrial health or aging?

There is no evidence that it does. The largest trial had 218 people with primary mitochondrial myopathy. It found no benefit over placebo on walking or fatigue. No trial has tested it in healthy people. ⁴

Why was the approval controversial?

The only placebo-controlled trial in Barth syndrome had 12 patients. It did not meet its main measures. The FDA first rejected the drug. It then approved it on a surrogate strength measure from the open-label extension. That pathway is normally used when a disease is rare and has no other treatment. ¹²

Which adverse reactions has the drug caused?

Injection-site reactions are common. Every patient in the Barth syndrome crossover trial had one while on the drug. No serious adverse events caused by the drug have been identified. But total human exposure is small. ¹²⁴

Citations

Thompson 2024, Genetics in Medicine: 168-week open-label extension of TAZPOWER, elamipretide in Barth syndrome doi.org
Forzinity (elamipretide) prescribing information drugs.com
2025, Orphanet J Rare Dis: psychometric evaluation of the Barth Syndrome Symptom Assessment in the TAZPOWER trial pubmed.ncbi.nlm.nih.gov
Karaa 2023, Neurology: efficacy and safety of elamipretide in primary mitochondrial myopathy (MMPOWER-3) pubmed.ncbi.nlm.nih.gov