Where to buy SS-31.

SS-31 became the third FDA-approved peptide in this Library when the agency green-lit Forzinity™ (elamipretide) for Barth syndrome in September 2025. The question of where to buy SS-31 now depends on the intended use — prescription, compounded, or research-grade. Three channels exist, and they are not interchangeable.

What the molecule actually is

SS-31 is a four-amino-acid peptide. The sequence is D-Arg-Dmt-Lys-Phe-NH₂. "Dmt" is 2',6'-dimethyltyrosine, an unusual residue we'll define in a moment. Two features make this molecule weird. It uses D-amino acids (the mirror-image form of normal amino acids), and it includes a non-standard residue most peptide suppliers can't synthesize cleanly.

The 2025 Tung et al. review describes elamipretide as a cell-permeable peptide that "selectively concentrates in the inner mitochondrial membrane, where it binds cardiolipin." Cardiolipin is the signature lipid of healthy mitochondria. SS-31 stabilizes cristae structure and supports the cardiolipin–cytochrome c supercomplex (Tung et al., 2025).

Stealth BioTherapeutics developed it through a real Phase III clinical-development program. In September 2025, the FDA granted accelerated approval to elamipretide under the brand name Forzinity. The approval is for adult and pediatric Barth syndrome patients weighing ≥30 kg. That makes elamipretide the third FDA-approved peptide in this encyclopedia, behind tesamorelin and bremelanotide (Shirley, 2025).

For a buyer, here's what matters. There are now three legal channels for "SS-31," and they're not the same product.

The three SS-31 channels in 2026

1. Prescription Forzinity (FDA-approved, September 2025)

Forzinity is the FDA-approved version of elamipretide. Stealth manufactures it under cGMP (current Good Manufacturing Practice, the FDA's quality standard for drugs). It's dispensed by prescription only, through specialty pharmacy, to Barth syndrome patients weighing ≥30 kg.

The approval rests on the TAZPOWER trial: 28 weeks of randomized testing, plus a 168-week open-label extension, with 8 of 10 patients reaching the extension endpoint (TAZPOWER OLE, 2024). The FDA requires post-marketing confirmatory trials. Pricing is orphan-drug territory: roughly $300,000 to $750,000 per patient per year. Insurance pre-authorization and patient-assistance programs run through Stealth and the specialty pharmacy.

2. 503A compounded elamipretide (now sharply limited)

503A is the section of federal law that lets compounding pharmacies make custom drug formulations for individual patients. Before September 2025, some 503A pharmacies prepared elamipretide for off-label use. The FDA approval changed that.

When a drug is FDA-approved as a finished product, 503A generally prohibits compounding pharmacies from making "essentially a copy" of it. The compounded-elamipretide channel that existed before approval is now largely closed, except under narrow shortage exceptions (FDA, Section 503A).

3. Research-grade SS-31 (Research Use Only)

Research-grade SS-31 is sold by chemical suppliers under Research Use Only labeling (21 CFR § 809.10(b)(9)) for laboratory use only. It's nominally the same tetrapeptide as Forzinity. But the manufacturing controls, quality assurance, and intended use are different.

Research-grade SS-31 is appropriate for in-vitro and animal-model work that matches the published literature. It's not equivalent to prescription Forzinity. Selling it for human consumption is illegal. This is the channel we cover for the rest of this guide.

SS-31 (Elamipretide)

Tetrapeptide 4 aa Cardiolipin-binding

The same D-Arg-Dmt-Lys-Phe-NH₂ tetrapeptide cited across the 2025 Tung et al. mechanism review and the TAZPOWER + MMPOWER-3 Phase III program. Chiral-HPLC verified D-arginine, observed mass [M+H]⁺ 640.8, ≥99% HPLC purity, ISO 17025 third-party CoA on every lot. Research Use Only — not the same product as prescription Forzinity.

View SS-31

How to verify research-grade SS-31

The standard eight criteria for any peptide vendor apply here. Four of them are sharper for SS-31, because this molecule has structural quirks most vendors aren't equipped to verify.

1. Confirm the D-arginine

The first residue is D-arginine. That's the mirror-image form of normal L-arginine. The D-form is what gives elamipretide two of its key properties: it resists breakdown by enzymes (proteolytic resistance), and it can cross cell membranes to reach mitochondria. If the synthesis used L-arginine instead, the material is not SS-31 — it is a related but inactive peptide.

The lab confirms D-arginine three ways: chiral HPLC, optical-rotation measurement, or amino-acid analysis after acid hydrolysis. If the CoA doesn't mention any of these, it's missing the most distinctive identity check for this peptide.

2. Confirm the Dmt residue

The second residue is 2',6'-dimethyltyrosine. That's a non-canonical amino acid: it's tyrosine with two extra methyl groups on the aromatic ring. It isn't sold as a standard building block. Suppliers either synthesize it themselves or source it from a specialty vendor.

Vendors who quietly substitute regular tyrosine (which is cheaper and off-the-shelf) aren't producing SS-31. The check: mass-spec at the expected mass, plus NMR or amino-acid analysis confirming Dmt specifically.

3. Mass-spec the molecule

The theoretical mass of SS-31 is ~639.79 g/mol. A research-grade CoA should report observed mass at [M+H]⁺ 640.8, within 0.3 Da of theoretical. If the observed mass is meaningfully different, the material is not SS-31. The likely substitution is regular tyrosine instead of Dmt, which produces a mass near 612 Da — a 28 Da gap representing the two missing methyl groups.

4. Lyophilized only — no sprays, no patches

Every Phase III trial (MMPOWER-3, TAZPOWER, PROGRESS-HF) used reconstituted lyophilized powder as the study formulation. Research-grade SS-31 should ship as a freeze-dried powder for reconstitution. Capsules, sublingual sprays, and transdermal patches have not been studied in any published trial. Pre-reconstituted liquid shipped without cold chain has already started degrading by the time it is received.

What research-grade SS-31 costs in 2026

SS-31 is one of the more expensive peptides per milligram in this Library. Not because it's long (it's only four residues). It's because two of those four are non-standard. The D-arginine must be sourced as the D-isomer specifically. The Dmt must be synthesized or bought from a specialty supplier. Both add real cost.

Representative 2026 pricing benchmarks for research-grade SS-31:

• 10 mg vial: $80–$150 ($8–$15/mg). The most common retail size.
• 20 mg vial: $130–$220 ($6.50–$11/mg). Better per-mg value for animal-model work.
• 50–100 mg lots: $300–$700 ($6–$8/mg). For academic and industry research groups.
• Prescription Forzinity: $300,000–$750,000 per patient-year. That's orphan-drug pricing, not retail markup.

Pricing below $50 per 10 mg vial is a quality signal worth investigating. The D-arginine and Dmt residues are genuine synthesis costs, and HPLC purification that separates crude material from research-grade product adds further cost. The low end of the SS-31 market frequently reflects substitution: L-arginine instead of D-arginine, regular tyrosine instead of Dmt, or both — producing a related peptide that is not SS-31. Pricing above $30/mg typically reflects retail margin rather than synthesis cost.

Legal status — what changed in September 2025

Before September 2025, elamipretide was a Phase III investigational drug. It was available only through clinical trials or through limited 503A compounding. Research-grade SS-31 was sold under Research Use Only labeling. That channel hasn't changed.

The FDA approval changed three things:

• Created the prescription Forzinity channel. Patients with confirmed Barth syndrome can now get elamipretide as a finished pharmaceutical product through specialty pharmacy, with insurance, post-marketing surveillance, and the rest of the drug infrastructure (Shirley, 2025).
• Closed most of the 503A compounded channel. 503A pharmacies generally can't produce "essentially a copy" of an FDA-approved drug. The compounded-elamipretide route that operated before approval is now largely unavailable.
• Didn't change research-grade. Research Use Only labeling under 21 CFR § 809.10(b)(9) still applies to chemical suppliers selling SS-31 for lab work. Approval of one finished product doesn't criminalize research-chemical synthesis of the underlying molecule.

For deeper context on the September 2025 approval, see our Forzinity FDA approval article.

Red flags to watch for

• No chirality verification on the CoA. If the lab didn't confirm D-arginine, they didn't check the most distinctive feature of this peptide.
• Mass-spec near 612 [M+H]⁺ instead of 640.8. That 28 Da gap is two missing methyl groups — the Dmt was substituted with regular tyrosine.
• "SS-31 for longevity" or "anti-aging." The only FDA-supported indication is Barth syndrome. Mouse functional data doesn't extrapolate to healthy adults.
• "Equivalent to Forzinity." Same molecule, different products, different oversight. Equivalence claims cross FDA jurisdiction.
• Capsules, sprays, or transdermal patches. Every Phase III trial used reconstituted lyophilized powder as the study formulation. Other delivery routes have not been studied in any published trial.
• Pre-reconstituted liquid without cold chain. Reconstituted SS-31 at room temperature has a much shorter shelf life than the dry powder.
• Internal-QC-only documentation. You want third-party ISO 17025 verification, not the vendor's own paperwork.

SS-31 (Elamipretide)

100 mg ≥99% pure Lyophilized

D-Arg-Dmt-Lys-Phe-NH₂ tetrapeptide, theoretical MW ~639.79. The same reference compound studied across the MMPOWER-3, TAZPOWER + 168-week OLE, and ongoing NuPOWER / ReCLAIM / PROGRESS-HF Phase III programs. COA with HPLC trace, mass-spec, and chiral verification ships with every order. Research Use Only.

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Frequently asked questions

Is SS-31 legal to buy in the USA?

Two channels, two answers. Prescription Forzinity is legal only with a Barth syndrome diagnosis, dispensed through specialty pharmacy with a physician prescription. Research-grade SS-31 from chemical suppliers is legal as a Research Use Only compound for laboratory work under 21 CFR § 809.10(b)(9). It is not the same product as Forzinity. Selling it for human consumption is illegal.

What's the difference between Forzinity and research-grade SS-31?

Forzinity is the FDA-approved version, made by Stealth under cGMP. It ships through specialty pharmacy with prescribing info, post-marketing surveillance, and insurance coverage. Research-grade SS-31 is the same tetrapeptide, made by chemical suppliers under Research Use Only labeling. The molecules are nominally identical. The manufacturing controls, quality systems, and intended use aren't.

How much should research-grade SS-31 cost?

Roughly $80–$150 per 10 mg vial, $130–$220 per 20 mg vial, and $300–$700 for 50–100 mg lots. SS-31 is short (four residues) but expensive to make because of the D-arginine and Dmt. Prescription Forzinity sits in the $300,000–$750,000 per patient-year orphan-drug range and isn't directly comparable.

What is Forzinity approved for?

The FDA granted accelerated approval in September 2025 for improvement of muscle strength in Barth syndrome patients ≥30 kg. The basis was the TAZPOWER 28-week RCT plus its 168-week open-label extension. Accelerated approval requires confirmatory trials after launch. Forzinity isn't approved for primary mitochondrial myopathy, dry AMD, heart failure, sarcopenia, or anti-aging.

What should an SS-31 Certificate of Analysis show?

HPLC purity ≥98% with the chromatogram. Mass-spec at observed [M+H]⁺ 640.8 (theoretical MW 639.79). Chiral-HPLC confirming D-arginine. NMR or amino-acid analysis confirming Dmt. Karl Fischer water content 2–8% for lyophilized material. Counterion content (usually acetate or trifluoroacetate). The testing lab should be ISO/IEC 17025 accredited and named on the report.

SS-31 vs MOTS-c — which one for research?

Different mechanisms, different evidence tiers. SS-31 is a synthetic tetrapeptide that binds cardiolipin in the inner mitochondrial membrane. It now holds FDA accelerated approval. MOTS-c is a 16-residue peptide encoded by mitochondrial DNA, with proposed AMPK-related metabolic effects. It has no FDA approval and stays an early-stage research target. SS-31's clinical program is an order of magnitude more mature. See SS-31 vs MOTS-c.

How should research-grade SS-31 be stored?

Lyophilized material should be stored at −20°C, protected from light, with a multi-year shelf life when properly handled. Once reconstituted, the solution should be stored at 2–8°C and used within 30 days. The D-amino acid residue confers proteolytic resistance in biological systems, but does not protect against hydrolysis or oxidation in solution.