SS-31 Peptide Benefits, Side Effects and FDA Approval: Research Data

What Is SS-31 (Elamipretide)?

SS-31 is a small synthetic peptide of four amino acids, one of the Szeto-Schiller peptides designed as cell-permeable antioxidants that concentrate in mitochondria.^[6] Its drug name is elamipretide; the approved product, elamipretide HCl, is sold under the brand name Forzinity.^[2] It was developed by Stealth BioTherapeutics, which renamed itself Mighty Therapeutics in June 2026.^[7][1]

Unlike MOTS-c, which the body makes from mitochondrial DNA, SS-31 does not occur naturally. For the full mechanism and trial history, see the SS-31 (elamipretide) research review.

How SS-31 Targets Mitochondria: Cardiolipin and Electron Transport

SS-31 targets mitochondria and binds cardiolipin, a phospholipid of the inner mitochondrial membrane. In isolated mitochondria and kidney ischemia models, this interaction protected cytochrome c function and re-energized mitochondria after injury.^[8] By stabilising the cytochrome c/cardiolipin complex, SS-31 supported electron transport and mitochondrial ATP production while limiting reactive oxygen species.^[9] Later work showed it binds lipid bilayers and changes the surface charge of the mitochondrial membrane, which may be a key part of its mechanism.^[10]

FDA describes the approved drug the same way: Forzinity binds to the inner part of the mitochondria, improving mitochondrial structure and function, and its label calls it a mitochondrial cardiolipin binder.^[1][2] Early papers also described antioxidant activity against oxidative stress.^[6]

SS-31 Peptide Benefits: Potential Benefits Studied

Barth Syndrome: The FDA-Approved Benefit

In the TAZPOWER trial, 12 patients with Barth syndrome received elamipretide or placebo in a 12-week crossover. Neither primary endpoint, the 6-minute walk test or the Barth symptom score, was met; improvements appeared later in the open-label extension.^[11] FDA’s label states that knee extensor muscle strength did not increase during the randomized trial but did increase during the extension period, and that is the measure behind the accelerated approval.^[2] FDA considers that improvement reasonably likely to predict benefit such as standing more easily or walking farther.^[1]

Skeletal Muscle, ATP Levels and Older Adults

In aged mice, SS-31 rapidly improved mitochondrial energetics and skeletal muscle performance, including fatigue resistance.^[12] In a randomized, placebo-controlled trial in 39 older adults, one exposure to elamipretide raised in vivo mitochondrial ATP production capacity in skeletal muscle relative to placebo.^[13] That is an energetics measure; the trial did not test muscle strength or exercise tolerance over time. A phase 2 trial in healthy aging is now recruiting.^[14]

Heart Function and Heart Failure

In aged mouse heart cells, SS-31 reduced elevated proton leak and improved mitochondrial function.^[15] Human heart trials have been negative on their main endpoints. In PROGRESS-HF (71 patients with heart failure with reduced ejection fraction), left ventricular end-systolic volume did not change compared with placebo after four weeks.^[4] In EMBRACE STEMI, elamipretide (then called MTP-131) did not reduce infarct size after heart attack, though it was well tolerated.^[16]

Mitochondrial Disease, Friedreich Ataxia and Dry AMD

MMPOWER-3, a phase 3 trial in 218 people with primary mitochondrial myopathy, did not meet its primary endpoints on the 6-minute walk test and fatigue.^[3] Smaller studies have covered Friedreich ataxia (a completed phase 1/2 study of 20 people) and a phase 3 trial in mitochondrial myopathy caused by nuclear DNA mutations.^[14] In dry AMD, the phase 2 ReCLAIM-2 trial (176 patients) missed its primary endpoints on visual acuity and geographic atrophy growth; the phase 3 ReNEW trial has enrolled 313 people with primary completion expected in August 2027.^[5][17]

Human Trials: How Much Clinical Evidence Exists?

More than for most research peptides. ClinicalTrials.gov lists 21 elamipretide studies, from phase 1 to phase 4, in heart failure, mitochondrial disease, Barth syndrome, eye disease and aging.^[14] The pattern in these clinical studies is consistent: elamipretide has been well tolerated apart from injection site reactions, but most large trials missed their primary endpoints, and the one approval is an accelerated approval for a rare disease.^[3][4][2] A randomized, placebo-controlled confirmatory trial in Barth syndrome, 4TAZPower, is now recruiting.^[18]

SS-31 Side Effects: Injection Site Reactions and Safety

Because elamipretide is an approved drug, its side effects are documented on an FDA label, which is rare for a research peptide.

• Injection site reactions. In the placebo-controlled Barth trial, injection site redness occurred in all 12 patients on elamipretide versus 3 of 12 on placebo, with pain, hardening, itching, bruising and hives also more common on the drug.^[2] Injection site reactions were also the most common adverse events in ReCLAIM-2.^[5]
• Hypersensitivity. Serious allergic reactions needing emergency treatment have been reported, including rash, skin lesions and cough; they can appear minutes to months after starting. Serious hypersensitivity to elamipretide is a contraindication.^[2]
• Eosinophilia. Eosinophil counts often rose in studies lasting 30 days or more, peaked around 90 days and returned to baseline; the rise was not linked to symptoms.^[2]
• Benzyl alcohol. Forzinity contains benzyl alcohol as a preservative and is not approved for use in newborns because of the risk of benzyl alcohol toxicity.^[2]
• Other trials. In MMPOWER-3 most adverse events were mild to moderate.^[3]

These adverse events come from the approved product given under medical supervision. Nothing in that record covers research-grade material.

Is SS-31 FDA Approved? Accelerated Approval and the FDA Label

SS-31 vs MOTS-c

Both are discussed as mitochondrial peptides, but they differ. SS-31 is a synthetic tetrapeptide that binds cardiolipin in the inner membrane and has a large human trial record and one FDA approval.^[9][1] MOTS-c is a 16-amino-acid peptide encoded in mitochondrial DNA that acts through AMPK and has no published human treatment trial. See MOTS-c vs SS-31 and MOTS-c benefits and side effects.

What SS-31 Research Does Not Yet Show

• Confirmed clinical benefit. Even in Barth syndrome, benefit on daily function awaits the confirmatory trial.^[1][18]
• Benefit in common diseases. Trials in heart failure, primary mitochondrial myopathy and dry AMD missed their primary endpoints so far.^[4][3][5]
• Anti-aging effects in people. The older-adult data are one-dose energetics; aged-mouse results have not been tested as long-term outcomes in humans.^[13][12]

A 2025 review describes elamipretide’s potential across mitochondrial dysfunction and pathological conditions, while noting that this is still being tested.^[20]

SS-31 for Laboratory Research

Remy Research supplies SS-31 for in-vitro research as the SS-31 40mg pen, the SS-31 research vial (10mg or 50mg), the Genovare SS-31 100mg AQ pen and the Genovare SS-31 + MOTS-c 42mg AQ pen. Each product page carries its batch testing details. For UAE availability, see the SS-31 Dubai guide.