SS-31 peptide (elamipretide)

What is the SS-31 peptide?

SS-31 is elamipretide, a four-amino-acid peptide that the label calls a "mitochondrial cardiolipin binder".^[3]

Sequence

D-Arg-2,6-dimethyl-Tyr-Lys-Phe-NH₂; every residue is L except the D-arginine^[3]

Formula and weight

C₃₂H₄₉N₉O₅, 639.8 g/mol (free base); the drug is the hydrochloride salt, 749.2 g/mol^[14][3]

Other names

SS-31, SS31, MTP-131, Bendavia^[14]

Brand

Forzinity (Stealth BioTherapeutics), NDA 215244^[1]

Its 2,6-dimethyl-tyrosine is not one of the 20 standard amino acids, so the sequence molecular weight calculator cannot model it.

SS-31 dosage on the Forzinity label

The label dose is 40 mg once daily under the skin, which is 0.5 mL of the 80 mg/mL solution; patients with severely reduced kidney function take 20 mg.^[3]

The calculator above reproduces the label: 280 mg in 3.5 mL is 80 mg/mL, and 40 mg is 0.5 mL. The units are only the U-100 arithmetic equivalent of the label's volumes.

The approval: accelerated, with conditions

The FDA granted accelerated approval on September 19, 2025, based on knee-extensor muscle strength, an intermediate endpoint, and required a confirmatory trial.^[2][4]

• First of its kind. The FDA called it "the first treatment for Barth syndrome".^[4]
• Conditions. "Continued approval for this indication may be contingent upon verification and description of clinical benefit in a confirmatory trial." The required randomized, placebo-controlled trial has a final report due in 2030.^[3][2]

What the trials showed

In its randomized trial elamipretide did not beat placebo on its main outcomes; the approval rests on muscle-strength results.^[3][5]

Side effects on the label

Injection-site reactions were near-universal in the trial; the label also warns of serious allergic reactions.^[3]

Eosinophil counts rose frequently with 30 days or more of use and returned to baseline later, without clinical findings.^[3]

"Research" SS-31 and compounding

Approval of Forzinity does not make other SS-31 products legal: in August 2026 the FDA called "SS-31" sold by four research-peptide sellers unapproved new drugs.^{[8][9][10][11]}

• In December 2025 the FDA told an API distributor that elamipretide acetate is "ineligible for use in human drug compounding under sections 503A".^[12] The approved product is the hydrochloride salt; we found no FDA statement on compounding with it.
• WADA 2026 does not name elamipretide, and as an approved drug it falls outside the S0 class for non-approved substances.^[13]

Other peptide pages

The peptides most often looked up alongside this one. Each page gives that peptide's FDA status, compounding status and published human evidence, with sources; the status table has all 23 in one place.

• MOTS-cNot approved 16-amino-acid mitochondrial peptide. No human trials of MOTS-c itself.
• CagrilintideNot approved Amylin analogue; CagriSema under FDA review.
• BPC-157Not approved 15-amino-acid peptide. Human data: a few tiny, uncontrolled studies.
• TB-500Not approved A 7-amino-acid fragment of thymosin beta-4. No human trials of TB-500 itself.
• BPC-157 + TB-500 blendNot approved Two peptides in one vial: the arithmetic of a fixed ratio.
• TesamorelinFDA-approved Egrifta SV and Egrifta WR. Labeled doses, diluents and volumes.