Elamipretide (SS-31)

Elamipretide (SS-31) is a synthetic tetrapeptide (four amino acids) that selectively targets the inner mitochondrial membrane, where it binds reversibly to cardiolipin — a phospholipid critical to the structural integrity of the inner mitochondrial membrane and the function of the electron transport chain. By stabilizing cardiolipin, elamipretide is proposed to improve mitochondrial cristae architecture, reduce electron leakage and reactive oxygen species (ROS) production, and improve ATP synthesis efficiency. It is the first mitochondria-targeted therapeutic to receive FDA approval and the first approved treatment for Barth syndrome.¹

Elamipretide was developed over more than a decade by Stealth BioTherapeutics (now Stealth BioTherapeutics Inc.) and has been studied in multiple clinical trials across several conditions including Barth syndrome, heart failure, primary mitochondrial myopathy, dry age-related macular degeneration, and others. In the research peptide and longevity communities, it is known primarily as SS-31 and has attracted interest for its mitochondrial optimization and anti-aging potential.

On September 19, 2025, the FDA granted accelerated approval to Forzinity (elamipretide) injection to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg. Barth syndrome is an ultra-rare, life-limiting X-linked genetic disease affecting approximately 150 individuals in the United States, characterized by cardioskeletal myopathy, neutropenia, and mitochondrial dysfunction caused by mutations in the TAZ gene affecting cardiolipin remodeling.¹

This approval is under the FDA's accelerated approval pathway, based on an intermediate clinical endpoint (improvement in knee extensor muscle strength). Continued approval may be contingent upon verification of clinical benefit in a confirmatory trial.

All uses of elamipretide outside of Barth syndrome in patients meeting the weight threshold are off-label and not FDA-approved. This includes use for heart failure, general mitochondrial optimization, anti-aging, and athletic performance, which remain investigational.

In the research peptide and longevity medicine community, elamipretide is used primarily for its proposed mitochondrial optimization and anti-aging potential — all off-label uses. It has been studied in small trials for several mitochondrial and age-related conditions, where preliminary results have been mixed.

The FDA-approved dose for Barth syndrome is 40 mg subcutaneously once daily, administered at the same time each day.¹ Off-label and research use protocols vary and are not derived from validated clinical data.

Subcutaneous injection.

Specific storage requirements are documented in the Forzinity prescribing information. Refrigerate as directed; protect from light.¹

From the FDA-approved label and clinical trial data:¹

• Injection site reactions: The most common adverse effects are injection site reactions (erythema, pain, induration, pruritus, bruising, urticaria), treatable with oral antihistamines or topical corticosteroids.
• Hypersensitivity: Signs or symptoms of immediate hypersensitivity require discontinuation and immediate medical attention.
• Accelerated approval status: The approval is conditional on a confirmatory trial verifying clinical benefit. This means the evidence base, while sufficient for accelerated approval in a rare disease with high unmet need, is not the same standard as full approval.
• Off-label use accessibility: Because the approved indication is for a rare genetic disease and the manufacturer's production capacity may be primarily directed toward that population, access for off-label use may be limited. The regulatory landscape for off-label prescribing of elamipretide outside Barth syndrome is evolving.