SS-31: Forzinity’s approval, evidence and limits

Most peptides sold for longevity have never been approved for anything. SS-31 is the exception that causes confusion. Under the name elamipretide it became an FDA-approved drug in September 2025 ^[2]. The approval covers one rare inherited disease, Barth syndrome, and nothing else ^[1]. Some pages online still call SS-31 unapproved; others call it "the first FDA-approved mitochondrial peptide" without saying for what. This page sets out what the approval says, what the trials found and what has never been tested.

SS-31 is elamipretide, a peptide built to reach mitochondria

SS-31 is a four-amino-acid peptide designed to settle in the inner membrane of mitochondria, the parts of the cell that make energy. The label calls it a "mitochondrial cardiolipin binder" that "improves mitochondrial morphology and function" ^[1]. Cardiolipin is a fat found almost only in that inner membrane, and it helps hold the energy-making machinery together.

The names can be confusing. SS-31 was the lab code; MTP-131 and Bendavia were earlier development names; elamipretide is the generic name; Forzinity is the brand Stealth BioTherapeutics sells ^[2]. They all point to the same molecule. A product sold online as "SS-31" is a different matter, covered below.

What FDA approved, word for word

FDA approved Forzinity "to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg" ^[1]. The label describes Barth syndrome as a rare, X-linked, recessive genetic disorder that is not likely to affect females ^[1]. Every patient in the trial program was male.

This indication is approved under accelerated approval based on an improvement in knee extensor muscle strength, an intermediate clinical endpoint. Continued approval for this indication may be contingent upon verification and description of clinical benefit in a confirmatory trial.^[1]

Accelerated approval is a pathway for serious conditions with few treatments. FDA can approve a drug on a measure that is expected to predict real benefit, here knee-muscle strength, before that benefit is proven. The company then has to confirm it in another trial. If the confirmation fails, the approval can be withdrawn. FDA’s approval announcement requires a confirmatory placebo-controlled trial ^[2].

What the Barth syndrome trial showed

In the 12-week randomized phase, elamipretide did not beat placebo on walking distance or fatigue; strength gains were seen in the open-label extension. Those are the label's own words in plainer form: the drug "was not superior to placebo on these primary endpoints" ^[1].

The trial enrolled 12 people with genetically confirmed Barth syndrome, aged 12 or older. Each took the drug and placebo in turn, in random order. After 12 weeks on the drug, median knee-muscle strength had changed by 4 newtons, against a 5-newton fall on placebo ^[1]. Ten people then continued on open-label drug. By week 168, the 8 still taking it had a median gain of 63 newtons over their starting strength ^[1].

A published report on the same extension found walking distance on the 6-minute walk test up 315 feet (96.1 meters) from the start of the extension at week 168 (P=.003) ^[5]. That is an observed within-group improvement, without a concurrent control that could establish the treatment’s contribution. It is also uncontrolled: everyone knew they were on the drug, and there was no placebo group to compare with.

Trials in other conditions missed their goals

Elamipretide has been tested in bigger groups than the Barth trial, and those trials did not succeed. That matters because the bigger trials are closer to the broad "mitochondrial health" story told about SS-31 online.

• Primary mitochondrial myopathy (MMPOWER-3). 218 adults, randomized and placebo-controlled for 24 weeks. Walking distance differed from placebo by −10.5 feet (−3.2 meters;95% CI −61.4 to 40.4 feet [−18.7 to 12.3 meters];P=.69), and fatigue scores did not differ. The authors wrote that it "did not improve outcomes" ^[6].
• Dry age-related macular degeneration (ReCLAIM-2). 176 people with geographic atrophy, 48 weeks. The drug did not reach significance on either primary measure, low-light vision or growth of the atrophy area. Some secondary retinal measures looked better ^[7].

Older-adult research does not establish longevity benefit

A 2021 randomized double-blind trial enrolled 39 healthy adults aged 60–85 selected for low mitochondrial function. Immediately after infusion, percentage change in mitochondrial ATP capacity favored elamipretide (P=.045), while the absolute-change comparison was P=.055. The between-group difference was absent at day 7, and fatigue resistance did not significantly improve ^[8]. This is human aging-related physiology research, but it does not establish longer life, a general energy benefit or durable functional improvement.

Safety: what the label warns about

The most common problem on the label is injection-site reactions, and in the small Barth trial nearly everyone had one. Redness at the injection site affected 12 of 12 people on the drug and 3 of 12 on placebo; hardening, itching and pain were also more common ^[1].

• Allergic reactions. Serious hypersensitivity reactions needing emergency care have been reported, with rash, skin lesions and cough. They can start within minutes or months after treatment begins ^[1].
• Contraindication. People with a serious hypersensitivity to elamipretide or any ingredient should not use it ^[1].
• Benzyl alcohol. The solution contains benzyl alcohol as a preservative, and the label says not to use it in newborns ^[1].
• Eosinophils. White-cell counts called eosinophils often rose with use of 30 days or more, peaking around 90 days, without symptoms in the trials ^[1].

These findings concern the approved product and the populations actually studied. They do not establish the safety of an online vial with uncertain contents or a long-term wellness regimen. Label rates from a 12-person crossover trial also should not be used to predict the exact risk for a different patient ^[1].

"Research" SS-31 isn't Forzinity

A vial labeled research-use-only is not established as approved Forzinity merely because it claims the same molecule. The approved application concerns a defined formulation, manufacturing controls and labeling. Neither a generic name nor a seller certificate establishes that an online vial has those characteristics. Product identity, clinical evidence and regulatory status must be evaluated separately ^[9].

Forzinity’s FDA-approved indication is narrow ^[1]. The ingredient’s absence from a nomination list alone cannot establish that every form of compounding is unlawful, particularly when it is a component of an approved drug. Compounding depends on all applicable requirements, including the actual substance, product and circumstances; compounded drugs are not FDA-approved ^[9]. A clinic’s use of the name SS-31 does not identify whether it offers approved Forzinity, an eligible compounded preparation or a research chemical. Ask for the exact product, dispensing source and basis for the proposed treatment.

SS-31 and MOTS-c: two "mitochondrial peptides" with different records

Elamipretide and MOTS-c are discussed as mitochondrial peptides, but their evidence and regulatory records differ. Elamipretide has a narrow approved product; native MOTS-c is not FDA-approved. The current 120-estimated-participant MOTS-c protocol is recruiting and has no posted results ^[10]. The MOTS-c status guide and safety guide distinguish registration from results and authorization.

The reviewed sources do not establish a controlled clinical benefit for an SS-31/MOTS-c combination. Mechanistic overlap does not supply interaction or safety data. For another compound marketed for cellular energy, see NAD+ and MOTS-c versus NAD+; the provider-check methodology separates marketing from clinical evidence.

SS-31 and FDA: the dates

Terms used on this page