Compounds / SS-31
SS-31
Also known as: Elamipretide; Forzinity; MTP-131; SS-31; Szeto-Schiller peptide 31; elamipretide HCl; CAS 736992-21-5
Primary research focus: Improving muscle strength in Barth syndrome; investigational for other mitochondrial diseases
Last updated July 2026 · Reviewed against FDA labeling and published research.
What is SS-31?
SS-31 (elamipretide) is a mitochondria-targeted tetrapeptide from the Szeto-Schiller family that penetrates cell membranes and binds cardiolipin, a key lipid of the inner mitochondrial membrane. In September 2025 the FDA granted it accelerated approval as Forzinity to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg. It is the first FDA-approved therapy for Barth syndrome and the first approved mitochondria-targeted therapeutic.
Elamipretide readily crosses cell membranes and concentrates at the inner mitochondrial membrane, where it binds reversibly to cardiolipin. Cardiolipin confers the folded cristae shape of the inner membrane, organizes the supercomplexes of the electron transport chain, and is essential to efficient electron transport; in Barth syndrome, mutations in the TAFAZZIN gene disrupt cardiolipin remodeling. By binding and stabilizing cardiolipin, elamipretide is thought to restore membrane architecture and improve electron transport efficiency and cellular bioenergetics, reducing electron leak and oxidative stress. It was originally characterized as an antioxidant, but the cardiolipin-targeting mechanism is now considered primary. Notably, the Szeto-Schiller peptides are described as improving function in aging and disease models without effect on the normal healthy organism.
How it’s supplied
Brand / trade names: Forzinity
Supplied as the FDA-approved product Forzinity (elamipretide hydrochloride) for subcutaneous injection, indicated for patients weighing at least 30 kg. It is a prescription medicine distributed through the manufacturer's channels. Research-grade SS-31 sold online is not the FDA-approved product and has not been evaluated by the FDA for identity, purity, or potency.
Dosage Chart
Units shown are for a U-100 insulin syringe (100 units = 1 mL), calculated from the vial size and BAC water you select. Always confirm against your prescription and your syringe markings.
| Phase | Dose | Frequency | Notes |
|---|---|---|---|
| Weeks 1-6 | 5mg | 1x Daily | — |
| Weeks 7-12 | 10mg | 1x Daily | — |
- Rotate injection sites to reduce irritation and lipohypertrophy
- Not for use during pregnancy or breastfeeding
- Do not exceed the recommended dose to try to speed results
Potential Benefits and Side Effects
Effects reported in published research. Not a promise of results, and not medical advice.
- Established for the approved indication; broader mitochondrial and anti-aging uses are investigational or unsupported.
- Improves muscle strength in adults and children with Barth syndrome weighing at least 30 kg (FDA-approved indication).
- Binds and stabilizes cardiolipin, restoring inner mitochondrial membrane architecture and electron transport efficiency.
- Preclinical increases in ATP and oxidative phosphorylation with reduced muscle fatigue in aging mice.
- Preclinical prevention of mitochondrial oxidative stress and muscle wasting in disuse atrophy models.
- Under investigation for dry age-related macular degeneration and primary mitochondrial myopathy.
- The most common adverse effects identified in clinical trials were mild-to-moderate injection site reactions.
- Refer to the current FDA prescribing information for the complete adverse reaction profile, which this summary does not replace.
- Long-term safety continues to be characterized under the accelerated approval framework.
Warnings and contraindications
Important safety information. This is not exhaustive — read the full prescribing information and consult your prescriber or pharmacist.
- Based on the approved product context and its regulatory history.
- Forzinity received accelerated approval; continued approval for this indication may be contingent upon verification of clinical benefit in confirmatory trials.
- The approval was contested: in an October 2024 briefing document FDA staff stated the agency did not believe the available evidence established effectiveness for Barth syndrome, though the Cardiovascular and Renal Drugs Advisory Committee subsequently voted 10 to 6 that elamipretide is effective.
- The approved indication is narrow: improving muscle strength in Barth syndrome in patients weighing at least 30 kg. Use for general anti-aging, mitochondrial optimization, or athletic performance is not an approved use and is not supported by approval-grade evidence.
- The most common adverse effects in clinical trials were mild-to-moderate injection site reactions.
- Research-grade SS-31 obtained outside the approved product is unregulated and not quality-assured.
- Consult the current FDA prescribing information for complete warnings, which this summary does not replace.
- Refer to the current FDA prescribing information for Forzinity. Known hypersensitivity to elamipretide or product components is a general precaution.
Reconstitution Steps
How to prepare the lyophilized vial. Confirm specifics with your pharmacist or prescriber.
- Follow the FDA-approved prescribing information for Forzinity, which supersedes any general guidance. The steps below describe general handling for a lyophilized subcutaneous peptide product.
- Confirm the product, strength, and expiration date before starting.
- Wash your hands and gather supplies: the vial, the diluent specified in the labeling, an alcohol swab, and a sterile syringe.
- Let refrigerated components reach room temperature as directed.
- Wipe the vial stopper with a fresh alcohol swab and let it dry.
- Add the specified diluent volume slowly down the inside wall of the vial.
- Do not shake. Gently swirl or roll until fully dissolved.
- Inspect the solution: it should be clear with no visible particles. Do not use if cloudy or discolored.
- Note the resulting concentration for reference, then store as directed in the labeling and use within the stated in-use window.
US regulatory status
Classifications are public record but can change. For reference only, not legal advice.
Development: Elamipretide came out of the chance discovery by Hazel Szeto and Peter Schiller of a family of aromatic-cationic peptides (the Szeto-Schiller or SS peptides) that selectively target mitochondria. Stealth BioTherapeutics developed it under the codes MTP-131 and SS-31. Preclinical work showed it prevented mitochondrial oxidative stress and muscle wasting in disuse atrophy models and, in aging mice, a single injection increased ATP and oxidative phosphorylation and reduced muscle fatigue. Its regulatory path for Barth syndrome (an ultra-rare mitochondrial cardioskeletal disease affecting roughly 150 people in the US, incidence approximately 1 in 300,000 to 400,000, primarily males) was contentious: FDA staff issued a briefing document in October 2024 stating the available evidence did not establish effectiveness, but the Cardiovascular and Renal Drugs Advisory Committee voted 10 to 6 in favor; FDA then extended its review, missed the April 2025 action date, and cited observations from a May 2025 CGMP inspection of a third-party manufacturing facility before granting accelerated approval on September 19, 2025. Stealth is studying elamipretide in additional indications including dry age-related macular degeneration and primary mitochondrial myopathy, and is developing a second-generation candidate.
Notes: SS-31 (elamipretide) is FDA-approved as Forzinity, granted accelerated approval on September 19, 2025 to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg. It is the first FDA-approved treatment for Barth syndrome and the first approved mitochondria-targeted therapeutic. It received priority review and rare pediatric disease designation; continued approval may be contingent on verification of clinical benefit in confirmatory trials. Because an FDA-approved product now exists, compounding a preparation that is essentially a copy of a commercially available drug product is generally not permitted under sections 503A or 503B, which materially narrows the prior compounded and research-chemical availability of SS-31. It is not a controlled substance. (Status current as of mid-2026.)
International status
Pharmacokinetics
Storage and handling
Important Notes
Practical considerations for consistency and safety.
- SS-31 is now an FDA-approved drug: elamipretide, marketed as Forzinity, approved September 2025 for Barth syndrome. This changes its status relative to older research-peptide framing.
- It is the first FDA-approved mitochondria-targeted therapeutic and the first therapy of any kind for Barth syndrome.
- The approval is narrow (muscle strength in Barth syndrome, at least 30 kg) and was granted via the accelerated pathway over an initial negative FDA staff assessment; confirmatory trials may be required.
- Because an approved product exists, compounding essentially a copy is generally not permitted, which narrows research-chemical and compounded availability.
- Anti-aging, mitochondrial optimization, and performance uses are not approved indications and are not supported by approval-grade evidence.
Lifestyle Factors
- Administered as a subcutaneous injection under specialist supervision for a rare mitochondrial disease.
- It is not a lifestyle, performance, or general anti-aging product.
References
Related compounds
Important disclaimer
This page is an educational reference, not medical advice, a diagnosis, or a treatment recommendation, and not a substitute for your prescriber or pharmacist. Approval and regulatory status varies by compound and can change. Always confirm against current prescribing information and consult a qualified healthcare professional before making any decision about a medication.