SS-31

Overview

SS-31 (elamipretide) is a mitochondria-targeted tetrapeptide (D-Arg-Dmt-Lys-Phe-NH2) developed by Hazel Szeto (Cornell) and clinically advanced by Stealth BioTherapeutics. It concentrates in the inner mitochondrial membrane by binding cardiolipin. In September 2025, the FDA granted accelerated approval to elamipretide (brand name FORZINITY) as the first therapy for Barth syndrome — the first FDA-approved mitochondria-targeted drug. It remains investigational for other indications.

Mechanism of Action

SS-31 selectively binds cardiolipin in the inner mitochondrial membrane and stabilizes the cytochrome c / cardiolipin complex. This preserves cristae structure and electron transport chain supercomplex organization, improving ATP production and preventing cytochrome c peroxidase activity that generates ROS at the source. It is not a conventional free-radical scavenger — the mechanism is cardiolipin-binding and ETC stabilization.

Research Summary

The original SS-peptide class was described by Zhao, Szeto and colleagues (J Biol Chem 2004, PMID 15178689), showing ~1000-fold concentration at the inner mitochondrial membrane and protection against oxidative cell death. Szeto's 2014 review (Br J Pharmacol, PMID 24117165) reframed the mechanism as cardiolipin-binding rather than antioxidant scavenging. The TAZPOWER trial (NCT03098797) in Barth syndrome, with its 168-week open-label extension (Thompson et al., Genet Med 2024, PMID 38602181), supported FDA accelerated approval of FORZINITY in September 2025 at 40 mg SubQ daily. The Phase 3 MMPOWER-3 trial in primary mitochondrial myopathy (Karaa et al., Neurology 2023, PMID 37268435) FAILED co-primary endpoints of 6-minute walk test and fatigue score, though a post-hoc nuclear-DNA subgroup showed improvement. Phase 2 ReCLAIM-2 in geographic atrophy missed primary endpoints but reduced ellipsoid-zone attenuation; a Phase 3 trial is ongoing. Earlier heart failure trials (PROGRESS-HF) showed only modest signals.

Vendors selling SS-31

Scored vendors carrying SS-31, ranked by trust grade. Grades are computed from indexed Certificates of Analysis. Full $/mg pricing is on the comparison page.

Prescribers who offer SS-31

17 prescribers in our directory work with SS-31, each confirmed from their own website. Peptides like SS-31 require a prescription from a licensed provider — telehealth options are available.

Reported Side Effects

• Injection site reactions (most common; can be managed with oral antihistamines or topical corticosteroids)
• Transient blurred vision (ocular)
• Headache
• Nausea
• Diarrhea

Compare SS-31 with Others

Research References

• Zhao K et al. Cell-permeable peptide antioxidants targeted to inner mitochondrial membrane inhibit mitochondrial swelling, oxidative cell death, and reperfusion injury (original SS-peptide report, J Biol Chem) (2004)
• Szeto HH. First-in-class cardiolipin-protective compound as a therapeutic agent to restore mitochondrial bioenergetics (Br J Pharmacol review) (2014)
• Karaa A et al. Efficacy and Safety of Elamipretide in Primary Mitochondrial Myopathy: The MMPOWER-3 Randomized Clinical Trial (Neurology) (2023)
• Thompson WR et al. Long-term efficacy and safety of elamipretide in Barth syndrome: 168-week open-label extension of TAZPOWER (Genet Med) (2024)
• Stealth BioTherapeutics announces FDA accelerated approval of FORZINITY (elamipretide) for Barth syndrome (press release, Sep 2025) (2025)

Frequently asked questions

Has SS-31 been independently lab-tested?

Disclosed Labs has collected 74 Certificates of Analysis (COA) for SS-31 from 12 independent testing labs. 24 vendors have submitted material for testing. Products average 99.8% tested purity across the corpus. Full testing data is available at https://www.disclosedlabs.com/peptides/ss-31/testing.

What is the average purity of SS-31 on the market?

Based on 74 COAs analyzed by Disclosed Labs, SS-31 products average 99.8% (±0.3%) tested purity. Individual vendor results vary; see per-vendor COA data at https://www.disclosedlabs.com/peptides/ss-31/coas.

Which labs have tested SS-31?

Independent labs that have tested SS-31 include: ILS Labs (Grade A). Full lab credibility grades and profiles are at https://www.disclosedlabs.com/labs.

Where can researchers source SS-31?

8 vendors with Disclosed Labs trust grades currently list SS-31, including Glacier Aminos, Ion Peptide, Peptide Partners. Compare live prices and lab-verified COAs at https://www.disclosedlabs.com/prices/ss-31.

Which prescribers offer SS-31 with a prescription?

17 prescribers in the Disclosed Labs directory work with SS-31, each confirmed from their own website, with telehealth options available. SS-31 requires a prescription from a licensed provider. Browse them at https://www.disclosedlabs.com/prescribers?peptide=SS-31.

How does SS-31 work?

SS-31 selectively binds cardiolipin in the inner mitochondrial membrane and stabilizes the cytochrome c / cardiolipin complex. This preserves cristae structure and electron transport chain supercomplex organization, improving ATP production and preventing cytochrome c peroxidase activity that generates ROS at the source. It is not a conventional free-radical scavenger — the mechanism is cardiolipin-binding and ETC stabilization.

What does the research say about SS-31?

The original SS-peptide class was described by Zhao, Szeto and colleagues (J Biol Chem 2004, PMID 15178689), showing ~1000-fold concentration at the inner mitochondrial membrane and protection against oxidative cell death. Szeto's 2014 review (Br J Pharmacol, PMID 24117165) reframed the mechanism as cardiolipin-binding rather than antioxidant scavenging. The TAZPOWER trial (NCT03098797) in Barth syndrome, with its 168-week open-label extension (Thompson et al., Genet Med 2024, PMID 38602181), supported FDA accelerated approval of FORZINITY in September 2025 at 40 mg SubQ daily. The Phase 3 MMPOWER-3 trial in primary mitochondrial myopathy (Karaa et al., Neurology 2023, PMID 37268435) FAILED co-primary endpoints of 6-minute walk test and fatigue score, though a post-hoc nuclear-DNA subgroup showed improvement. Phase 2 ReCLAIM-2 in geographic atrophy missed primary endpoints but reduced ellipsoid-zone attenuation; a Phase 3 trial is ongoing. Earlier heart failure trials (PROGRESS-HF) showed only modest signals.