SS-31 (Elamipretide)

What it is

SS-31 is the research name for elamipretide, a synthetic mitochondria-targeted tetrapeptide now approved in the United States under the brand name Forzinity for a narrow Barth syndrome indication^{[1 –2 ]}. The molecule was developed for mitochondrial dysfunction research because of its interaction with cardiolipin, a phospholipid enriched in the inner mitochondrial membrane^{[1 ,16 ]}.

FDA’s prescribing information states that Forzinity contains elamipretide, a mitochondrial cardiolipin binder, and lists the sequence as D-Arg-2,6-dimethyl-Tyr-Lys-Phe-NH2^{[1 ]}. All amino acid residues have the L configuration except arginine, which has the D configuration^{[1 ]}. The drug is supplied as a subcutaneous injection^{[1 ]}.

Elamipretide’s research history includes primary mitochondrial myopathy, Barth syndrome, heart failure, kidney and ischemia-reperfusion models, ophthalmology, and broader mitochondrial-disease hypotheses^{[6 –16 ]}. Many of those uses remain investigational even though Forzinity is now FDA-approved for Barth syndrome.

Barth syndrome is a rare, serious mitochondrial disease. FDA granted accelerated approval on September 19, 2025, making Forzinity the first FDA-approved treatment for Barth syndrome in patients meeting the label’s weight criterion^{[1 –2 ]}. This page separates the approved Barth syndrome indication from broader claims about fatigue, aging, exercise, mitochondrial optimization, or nonspecific “energy” benefits.

Regulatory status

Forzinity — accelerated approval for Barth syndrome

Forzinity (elamipretide) injection is FDA-approved to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg^{[1 ]}. The approval is accelerated approval based on improvement in knee extensor muscle strength, an intermediate clinical endpoint; the label states that continued approval may be contingent on confirmatory trial evidence of clinical benefit^{[1 ]}.

FDA announced the approval on September 19, 2025 and stated that the approval was based on improved strength of the muscle used to straighten the leg at the knee, which FDA considered reasonably likely to predict patient benefit^{[2 ]}. FDA also stated that a post-approval randomized, double-blind, placebo-controlled trial is required to confirm that the knee-strength changes translate into patient benefit^{[2 ]}.

Approved use is narrow

The approved product is not a general mitochondrial supplement. Elamipretide is not FDA-approved for primary mitochondrial myopathy, chronic fatigue, athletic performance, anti-aging, heart failure, macular degeneration, kidney disease, or wellness use^{[1 –2 ,6 –15 ]}.

Compounding and controlled-substance status

For compounding, FDA’s 503A and 503B rules still matter. State-licensed compounders and outsourcing facilities must follow the applicable bulk-substance and copy restrictions; the existence of an approved Forzinity product does not create a general right to compound elamipretide copies^{[3 –4 ]}. Any “compounded elamipretide” claim should receive legal review against live FDA lists, shortage status, essential-copy rules, and product-specific facts.

Elamipretide is not listed in federal controlled-substance schedules in 21 CFR Part 1308 as reviewed on May 7, 2026^{[5 ]}. Date of last regulatory verification: May 7, 2026.

Research summary

Primary mitochondrial myopathy — early signals, larger trial mixed

Primary mitochondrial myopathy trials established both promise and limitations. Karaa and colleagues conducted a randomized dose-escalation trial in adults with primary mitochondrial myopathy^{[6 ]}. A later randomized crossover trial suggested effects on patient-reported symptoms and functional outcomes^{[7 ]}. However, the larger MMPOWER-3 randomized clinical trial did not establish broad approval for primary mitochondrial myopathy, and later analyses focused on genotype-specific signals^{[8 –9 ]}. As of this review, primary mitochondrial myopathy remains investigational^{[1 ,8 –9 ]}.

Barth syndrome — accelerated approval evidence

Barth syndrome evidence supported accelerated approval. FDA’s Forzinity label describes a very small clinical development program: 12 male patients aged 12 to 35 years with genetically confirmed Barth syndrome received daily subcutaneous elamipretide in a randomized crossover study and open-label extension^{[1 ]}. Thompson and colleagues reported 168-week open-label extension results from TAZPOWER, and Hornby and colleagues published a natural-history comparison study^{[10 –11 ]}. The approval rests on an intermediate endpoint rather than definitive long-term clinical benefit^{[1 –2 ]}.

Heart failure — investigational

Heart failure research has not produced an approved indication. Daubert and colleagues conducted a randomized placebo-controlled trial of elamipretide in heart failure^{[12 ]}. Butler and colleagues reported the PROGRESS-HF phase 2 trial in reduced ejection fraction heart failure^{[13 ]}. These studies are scientifically relevant but do not establish elamipretide as an approved heart-failure treatment.

Ophthalmology — ReCLAIM-2

Ophthalmology research is also investigational. Ehlers and colleagues reported ReCLAIM-2, a randomized phase 2 trial evaluating elamipretide in age-related macular degeneration with geographic atrophy, visual function, and ellipsoid-zone outcomes^{[14 ]}. These data do not create an FDA-approved ophthalmology indication.

Mechanistic and review literature

Mechanistic and review literature describes cardiolipin-directed mitochondrial effects and broad therapeutic potential^{[15 –16 ]}. That literature should not be used to imply that elamipretide improves energy, longevity, exercise performance, or mitochondrial health in otherwise healthy people.

Editorial calibration

The approved Barth syndrome evidence should be presented with both significance and restraint. For a rare, serious mitochondrial disease with no prior FDA-approved treatment, an accelerated approval based on an intermediate endpoint is clinically meaningful and important from a regulatory standpoint^{[1 –2 ]}. At the same time, the labeled evidence base is small, male-only in the development program described by the label, and subject to confirmatory-trial requirements^{[1 –2 ]}.

The primary mitochondrial myopathy program illustrates why mechanism alone is insufficient. Elamipretide has a plausible mitochondrial target and early trial signals^{[6 –7 ]}, yet the larger randomized program did not produce a broad FDA-approved PMM indication^{[8 –9 ]}. This is a useful corrective to claims that cardiolipin targeting necessarily improves all mitochondrial symptoms.

For ProPeptideGuide, the editorial distinction should be explicit: Forzinity is an FDA-approved orphan-drug product for a defined Barth syndrome population^{[1 –2 ]}. SS-31 as a wellness, fatigue, exercise, longevity, or non-Barth “energy” peptide remains outside FDA-approved use and should not be described with the same certainty as the approved product.

Public discourse

George Tidmarsh, MD, PhD, Director of FDA’s Center for Drug Evaluation and Research, framed the Forzinity approval as part of FDA’s rare-disease access mission. This is an official regulatory communication, not personal medical advice^{[2 ]}.

No wellness or longevity podcast entries were included because accessible sources did not provide verifiable named quotes suitable for this section without drifting into unsupported use claims.

Public discourse reflects the views of the speakers cited and does not represent medical advice or the editorial position of ProPeptideGuide.

Side effects and safety

Adverse reactions on the Forzinity label

Forzinity’s FDA label identifies injection-site reactions as the most common adverse reactions^{[1 ]}. In the Barth syndrome clinical development program, local administration reactions were very common; the label reports injection-site erythema, pain, induration, pruritus, bruising, and urticaria more often with elamipretide than placebo in the crossover study^{[1 ]}.

Warnings and contraindications

The label includes warnings for benzyl alcohol toxicity in neonates and hypersensitivity reactions, including serious allergic reactions requiring emergency intervention^{[1 ]}. Forzinity is contraindicated in patients with serious hypersensitivity to elamipretide or any excipient^{[1 ]}.

Limited approval dataset

The approved dataset is small because Barth syndrome is rare. The label describes 12 male patients aged 12 to 35 years in the clinical development program, with open-label extension data in a subset^{[1 ]}. That limits the ability to detect rare or long-latency adverse effects.

Investigational uses

Safety for investigational uses cannot be inferred from the Barth syndrome label. Primary mitochondrial myopathy, heart failure, ophthalmology, anti-aging, and wellness uses involve different populations, risks, endpoints, and exposure contexts^{[6 –15 ]}. Long-term confirmatory clinical benefit for the approved Barth syndrome indication also remains subject to post-approval verification^{[1 –2 ]}.

Compounded vs. approved Forzinity

Compounded or research-chemical SS-31 should not be treated as interchangeable with Forzinity. FDA-approved Forzinity has a defined active ingredient, formulation, manufacturing standard, route, indication, label, and pharmacovigilance framework^{[1 ]}. Products sold outside that pathway may differ in identity, purity, sterility, excipients, concentration, and stability.

Available through

Forzinity is an FDA-approved prescription drug for the labeled Barth syndrome indication and should be accessed only through licensed clinicians and compliant pharmacy channels^{[1 –2 ]}.

No telehealth or clinic-platform listings are included in this draft. Listings should be added only after legal and editorial verification that a provider is appropriately diagnosing and treating Barth syndrome and dispensing the FDA-approved product through compliant channels.

ProPeptideGuide does not link to or endorse grey-market elamipretide, SS-31 research chemicals, or compounded copies marketed for anti-aging or mitochondrial optimization.