SS-31 (Elamipretide)

A mitochondria-targeting peptide for Barth syndrome

FDA-approved for a specific condition · specialist care only

Stylised model of the real sequence

Overview.

SS-31, generically elamipretide, is a synthetic mitochondria-targeting peptide that binds cardiolipin. Under the brand name FORZINITY it received FDA accelerated approval on 19 September 2025 to improve muscle strength in patients with Barth syndrome weighing at least 30 kg; continued approval depends on a confirmatory trial. Separately, unapproved 'SS-31' research-grade peptide is still sold online, entirely outside the approved drug's supply chain.

Also known as Elamipretide · Bendavia · MTP-131 · Ocuvia

The molecule, decoded.

Sequence: D-Arg-Dmt-Lys-Phe-NH2 (D-Arg-2',6'-dimethyl-L-tyrosyl-L-lysyl-L-phenylalaninamide)
Length: 4 residues
Molecular weight: 639.8 g/mol
Formula: C32H49N9O5
CAS number: 736992-21-5
Half-life: Not established
Routes studied: subcutaneous injection (approved route for FORZINITY), intravenous infusion (clinical pharmacology and drug-interaction studies described in the label)
Modifications: N-terminal D-arginine (D-amino acid); non-standard 2',6'-dimethyltyrosine residue; C-terminal amidation

How it works.

Elamipretide is a cell-permeable, cationic tetrapeptide (D-Arg-2',6'-dimethylTyr-Lys-Phe-NH2) that concentrates in the inner mitochondrial membrane and binds cardiolipin, stabilizing cristae structure, improving electron-transport-chain efficiency, and reducing reactive-oxygen-species production. In Barth syndrome, a genetic disorder of cardiolipin remodeling (TAZ gene), this is proposed to improve mitochondrial energetics in skeletal and cardiac muscle.

Evidence · FDA-approved · regulatory-grade trials

What the research shows

approval trial2025

FDA granted accelerated approval to elamipretide (FORZINITY) on 19 September 2025 to improve muscle strength in adult and pediatric Barth syndrome patients weighing at least 30 kg. The basis was an increase in knee-extensor strength (an intermediate endpoint) seen during the open-label extension of the TAZPOWER trial; in the 12-week randomized placebo-controlled crossover phase (n=12), elamipretide did not beat placebo on the primary endpoints (6-minute walk distance, fatigue score) and no strength gain was seen. Continued approval depends on a confirmatory randomized, double-blind, placebo-controlled trial in patients 5 years and older, due to complete in September 2029.

12 males aged 12-35 with genetically confirmed Barth syndrome (TAZPOWER crossover plus open-label extension)

Source

case report2026

In a compassionate-use case report, subcutaneous elamipretide given to a 5-year-old with genetically confirmed Barth syndrome and severe heart failure (LVEF 20%) was followed by improvement to LVEF 50%, reduction of mitral regurgitation to mild, and return to full-time school over 6 months, with one transient non-serious adverse event (abdominal pain with moderate pancreatic enzyme elevation).

single pediatric Barth syndrome patient, France (ANSM compassionate-use program)

Source

systematic review2026

A 2026 review of clinical development in primary mitochondrial diseases identified elamipretide (FORZINITY) as one of only four therapies to have achieved regulatory authorization for a primary mitochondrial disease as of its review date, alongside idebenone, taurine, and doxecitine/doxribtimine -- describing this cluster of approvals as an 'inflection point' after two decades of largely negative or inconclusive late-stage trials in the field.

review of 159 registered mitochondrial-disease trials (2010-2026)

Source

What to know first.

Based on: the FDA-approved label and approval trial for Barth syndrome; only anecdotal reports for unapproved research-chemical 'SS-31'.

Reported side effects

Injection-site reactions in all 12 treated patients in the placebo-controlled crossover (erythema 100% vs 25% on placebo; pain 75% vs 42%; induration 67% vs 17%; pruritus 67% vs 17%; bruising 25% vs 0; urticaria 25% vs 0) - label Table 2
Hypersensitivity reactions, including serious allergic reactions needing emergency treatment (rash, papular lesions, eczematous dermatitis, cough), occurring minutes to months after starting (Warnings 5.2)
Eosinophilia: eosinophil counts often rose with 30 or more days of use, peaking around day 90 and returning to baseline, without clinical findings
One transient, non-serious episode of abdominal pain with moderate pancreatic enzyme elevation in the pediatric compassionate-use case, which resolved without stopping treatment

Cautions

Contraindicated after serious hypersensitivity to elamipretide or any excipient; do not rechallenge after a serious reaction
Contains benzyl alcohol (20 mg/mL): not approved for neonates because of gasping-syndrome risk
Kidney impairment: the label gives separate instructions for adults with severe kidney impairment (eGFR <30 mL/min) not on dialysis; not studied in dialysis
Accelerated approval: continued marketing is contingent on a confirmatory trial not due to complete until 2029; FDA can withdraw approval if that trial fails to verify benefit
FDA required carcinogenicity studies (TgRasH2 mouse, 2-year rat) and a metformin (MATE1 substrate) drug-interaction study after approval; no carcinogenicity studies had been done at approval, and elamipretide inhibits MATE1 in vitro
Unapproved 'SS-31' research-chemical product sold online is not the same regulated supply chain as FORZINITY and has no corresponding safety oversight

Checked 2026-09

Where it stands.

FDA-approved for a specific condition · specialist care only. SS-31 (Elamipretide) is FDA-approved for a specific condition (Elamipretide (FORZINITY) has FDA accelerated approval to improve muscle strength in adults and children with Barth syndrome who weigh at least 30 kg) and managed through specialist care. RiptideRx doesn’t offer it.

FDA: Approved (accelerated approval): FORZINITY (elamipretide) injection, NDA 215244 (Stealth BioTherapeutics), approved 2025-09-19 'to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg.' Approval is under section 506(c) and 21 CFR 314.510 and depends on a required confirmatory randomized, double-blind, placebo-controlled trial in patients 5 years and older. The final protocol was submitted in 09/2025; the Phase 3b/4 4TAZPower trial (NCT07531251; registry start date 2 Jul 2026) is recruiting, with study completion targeted for 09/2029 and the final report for 03/2030. FDA could withdraw approval if the trial fails to verify clinical benefit. Other postmarketing requirements: 26-week TgRasH2 mouse and 2-year rat GLP carcinogenicity studies and a metformin drug-interaction PK study. Stealth also received a rare pediatric disease priority review voucher.
Approved products: FORZINITY (FDA, 2025): improve muscle strength in adult and pediatric patients with Barth syndrome weighing ≥30 kg (accelerated approval) Label
Compounding: Not applicable to FORZINITY itself (an FDA-approved NDA product). SS-31 was nominated for the 503A Bulks List by LDT Health Solutions, which withdrew the nomination on 20 Apr 2026 (FDA-2015-N-3534-0487); it was not on the July 2026 PCAC agenda and is not in any 503A category or on FDA's Category 2 page (updated 22 Apr 2026). Because elamipretide is now a component of an FDA-approved drug, 503A compounders may be able to use bulk elamipretide under section 503A(b)(1)(A)(i)(II), subject to the other 503A conditions, including limits on copies of commercially available drugs. Unapproved 'SS-31' sold online as a research chemical is outside any FDA pathway.
Sport (WADA): Not named in the WADA 2026 Prohibited List. Its mechanism (mitochondrial cardiolipin binding) does not fit the S1-S5 prohibited categories, and it now holds a governmental (FDA) therapeutic approval, which would place it outside the S0 'non-approved substance' criterion.
Enforcement: 24 Aug 2026: FDA warning letters to research-use-only peptide sellers Peptide Partners, Royal Peptides and Peak Performance Peptides listed SS-31 among the unapproved products they sold.

References (6)

SS-31 (Elamipretide)

Overview.

The molecule, decoded.

How it works.

What the research shows

What to know first.

Reported side effects

Cautions

Where it stands.

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