SS-31

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Snapshot

Chemistry and make-up

SS-31 is a very short tetrapeptide, but chemically it is not a “normal” peptide and that is the whole point. Two of its four residues are non-standard: it contains D-arginine (a D-amino acid, the mirror image of the natural L form) and Dmt = 2′,6′-dimethyltyrosine (a non-natural, methylated tyrosine). It is C-terminally amidated. The alternating basic/aromatic motif gives it a net positive charge and cell/mitochondrial permeability, letting it concentrate on the inner mitochondrial membrane and bind cardiolipin, the signature phospholipid of that membrane.

Those non-natural features matter for QC and identity. The D-arginine and Dmt mean ordinary L-amino-acid synthesis and standard sequence assumptions do not apply, and a real CoA must confirm the correct stereochemistry and the methylated tyrosine, not just the mass. The approved medicine is the hydrochloride salt (FORZINITY). Verify formula/MW against PubChem CID 11764719 (C32H49N9O5, ~639.8 g/mol), matching the brief.

What it is studied for (evidence)

• Mechanism (well characterised [A]): binds reversibly to cardiolipin on the inner mitochondrial membrane, protecting cristae structure and supercomplex assembly, improving mitochondrial respiration and ATP synthesis and reducing reactive oxygen species (TAZPOWER / mechanism review, PMC7935714) [A].
• Human clinical status (this one is real, and it is the honest highlight [A/B]): unlike most peptides in this space, elamipretide has been through genuine clinical trials and is now FDA-approved. On 19 September 2025 the FDA granted accelerated approval to FORZINITY (elamipretide HCl) to improve muscle strength in adult and paediatric patients (≥30 kg) with Barth syndrome, an ultra-rare genetic mitochondrial cardiolipin disorder. It is described as the first FDA-approved therapy that directly targets mitochondria (FDA press release; FDA approval letter NDA 215244) [B].
• Important caveats on that approval: it is accelerated approval based on an intermediate endpoint (knee-extensor muscle strength) in a tiny population (~150 patients in the US). The FDA’s Cardiovascular and Renal Drugs Advisory Committee voted 10 to 6 that the drug is effective on 10 October 2024 (a majority in favour, but a notably divided panel), and the pivotal TAZPOWER programme used a natural-history / baseline control rather than a concurrent randomised control. So the approval is narrow and confirmatory data are still expected; it is not broad proof of an anti-ageing or general “mitochondrial health” benefit (FDA CRDAC meeting, 10 Oct 2024) [B].
• Emerging / thin elsewhere: elamipretide has been trialled in other mitochondrial and age-related conditions (heart failure, primary mitochondrial myopathy, dry AMD, Friedreich’s ataxia) with largely disappointing or mixed results outside Barth syndrome. Broader efficacy is not established.
• Marketing claims vs data: research-chemical vendors sell “SS-31” as a general anti-ageing / energy / recovery peptide for humans. That extrapolates from one narrow rare-disease approval and preclinical work. The approved use is Barth syndrome muscle strength only; everything else is unproven for humans.

Handling, format and stability

Research SS-31 is supplied lyophilised for reconstitution in a research context only (no dosing guidance here). Store lyophilised cold and protected from light; reconstituted peptide is less stable and cold-chain dependent. The distinguishing handling issue is identity, not fragility: because the molecule contains a D-amino acid and a methylated tyrosine, a research batch can be mis-synthesised (wrong stereochemistry, unmethylated tyrosine) and still hit roughly the right mass, so MS alone is not enough.

Regulatory and trade status

• US: now an FDA-approved prescription drug (FORZINITY) for Barth syndrome. That changes its character, because “SS-31” sold as a research chemical is the unapproved version of an approved active ingredient, which raises regulatory exposure well above a typical never-approved peptide.
• UK/EU: not (yet) an approved medicine in the same way; research-use only in this market. Because it is now a known drug substance, any human/treatment framing is high risk and should be avoided.
• WADA (sport): elamipretide is not explicitly named on the 2026 Prohibited List, and its mitochondrial/cardiolipin mechanism does not map to any listed performance category. Note that because elamipretide now has FDA approval (Forzinity), the S0 “non-approved substances” catch-all no longer cleanly applies to it (S0 covers substances with no approval by any regulatory health authority). So it is not obviously prohibited by name; athletes should still confirm with their anti-doping authority before use (WADA 2026 Prohibited List) [B].
• Customs/labelling: being an approved-drug active ingredient increases scrutiny; identity/stereochemistry labelling matters.

Sources

• [B] FDA — Accelerated Approval, first Barth syndrome treatment (Sep 2025) — https://www.fda.gov/news-events/press-announcements/fda-grants-accelerated-approval-first-treatment-barth-syndrome
• [B] FDA approval letter, NDA 215244 (FORZINITY) — https://www.accessdata.fda.gov/drugsatfda_docs/appletter/2025/215244Orig1s000ltr.pdf
• [B] FDA Cardiovascular and Renal Drugs Advisory Committee, 10 Oct 2024 (10-6 effective vote) — https://www.fda.gov/advisory-committees/advisory-committee-calendar/october-10-2024-meeting-cardiovascular-and-renal-drugs-advisory-committee-10102024
• [A] TAZPOWER phase 2/3 + open-label extension in Barth syndrome (PMC7935714) — https://pmc.ncbi.nlm.nih.gov/articles/PMC7935714/
• [A] TAZPOWER trial record, NCT03098797 — https://clinicaltrials.gov/study/NCT03098797
• [B] Stealth BioTherapeutics FORZINITY approval announcement — https://www.prnewswire.com/news-releases/stealth-biotherapeutics-announces-fda-accelerated-approval-of-forzinity-elamipretide-hcl-the-first-therapy-for-progressive-and-life-limiting-ultra-rare-genetic-disease-barth-syndrome-302562058.html
• [B] PubChem CID 11764719 (elamipretide)
• [D] Research-chemical vendor “SS-31” pages — commercial; publish dosing and general anti-ageing claims, which we do not use.

Plain summary

SS-31 (elamipretide) is a four-amino-acid mitochondrial peptide that is chemically unusual, because it contains a D-amino acid and a non-natural methylated tyrosine (Dmt) and works by binding cardiolipin inside mitochondria to improve energy output. It is the standout of this group because it actually reached the clinic: in September 2025 the FDA gave its hydrochloride salt (FORZINITY) accelerated approval for the ultra-rare Barth syndrome, the first mitochondria-targeting drug approved. Be honest that this approval is narrow, on an intermediate endpoint, in ~150 patients, and split at advisory committee, so vendor claims of SS-31 as a general anti-ageing or recovery peptide are not supported, and its status as an approved-drug active raises the regulatory stakes for selling it as a research chemical.

For laboratory and research use only (RUO). Not for human or veterinary use, not for consumption, and not a medicine. Information is a research summary, not medical advice, and contains no dosing guidance.

For laboratory research use only. Not for human or veterinary use, not for consumption, and not a medicine. This is a research summary, not medical advice, and contains no dosing guidance.