SS-31 (Elamipretide) FDA Approved

What It Is

SS-31 is a synthetic tetrapeptide with the sequence D-Arg-Dmt-Lys-Phe-NH₂ (where Dmt is 2',6'-dimethyl-L-tyrosine). It is the best-characterized member of the Szeto-Schiller (SS) family of mitochondria-targeting peptides developed in the 1990s and 2000s by Hazel Szeto and Peter Schiller at Cornell University. Under the clinical name elamipretide, it was developed by Stealth BioTherapeutics through a multi-indication clinical program culminating in FDA accelerated approval in September 2025 as Forzinity^® for the treatment of Barth syndrome — a rare X-linked mitochondrial disorder caused by TAFAZZIN gene mutations affecting cardiolipin remodeling. This approval made elamipretide the first FDA-approved drug that directly targets mitochondrial function.

What distinguishes SS-31 from nearly every other peptide in the Kalios database is the novelty of its mechanism: it selectively accumulates in the inner mitochondrial membrane — not via receptor binding, but through physical affinity for cardiolipin, the signature phospholipid of the inner mitochondrial membrane, which is present at extremely low concentration elsewhere in the cell. SS-31 carries a net positive charge at physiological pH and is lipophilic enough to cross both the outer and inner mitochondrial membranes and concentrate in the cardiolipin-rich inner leaflet at 1,000–10,000× its cytoplasmic concentration. Once bound to cardiolipin, SS-31 stabilizes the inner membrane structure, preserves cristae architecture, protects cardiolipin from peroxidation, and improves electron-transport-chain efficiency (Birk et al., J Am Soc Nephrol 2013; PMID 23813215).

Clinically, SS-31 has been studied across a broader range of indications than its Barth syndrome approval suggests: heart failure (PROGRESS-HF), ischemia-reperfusion injury (EMBRACE-STEMI), dry age-related macular degeneration (ReCLAIM), primary mitochondrial myopathy (MMPOWER-3), and aged-muscle fatigue. Most of these Phase 2/3 programs produced mixed results — sometimes meeting exploratory endpoints while failing primary endpoints. Barth syndrome was the indication where the cardiolipin-specific mechanism converged most directly with the disease biology, and where the 168-week open-label extension TAZPOWER data ultimately supported accelerated FDA approval.

In the Kalios context, SS-31 is one of the very few community-used peptides with a formal FDA approval, which puts it in an unusual regulatory position: the approved use (Barth syndrome) is rare and narrowly defined, but the mechanism (cardiolipin stabilization, mitochondrial protection) has broad theoretical application to virtually any disease involving mitochondrial dysfunction. Off-label community use for anti-aging, heart failure support, skeletal-muscle fatigue, and macular degeneration is supported by mechanism and Phase 2 signals but is not within the approved label.

Mechanism of Action

SS-31's mechanism is distinct from essentially any other peptide in the community lexicon. Its core action is a physical-chemical interaction with cardiolipin, with downstream consequences across mitochondrial structure and function.

• Cardiolipin binding at inner mitochondrial membrane — SS-31 binds cardiolipin via electrostatic and hydrophobic interactions. Because cardiolipin is concentrated in the inner mitochondrial membrane and essentially absent elsewhere, this produces profound tissue-compartment specificity without requiring receptor recognition (Szeto, AAPS J 2006; PMID 16796378).
• Cristae-structure preservation — Cardiolipin is the lipid that shapes the curvature of inner mitochondrial cristae. SS-31 stabilizes that curvature, preserving the folded morphology that maximizes respiratory-chain packing density and ATP synthesis capacity.
• Cardiolipin peroxidation protection — Cardiolipin's four unsaturated fatty-acid tails make it exceptionally vulnerable to oxidation by reactive oxygen species generated during electron transport. Oxidized cardiolipin releases cytochrome c and initiates apoptosis. SS-31 protects cardiolipin from peroxidation without itself acting as a generic antioxidant — the mechanism is "protect cardiolipin integrity," not "scavenge ROS."
• Electron-transport-chain efficiency — Preserved cardiolipin organization keeps complex III and complex IV in productive association with their substrates. SS-31 improves ATP production efficiency in mitochondria with damaged membranes.
• Reduced ROS generation at source — An inefficient ETC leaks electrons and generates more ROS. By restoring ETC efficiency, SS-31 indirectly reduces ROS production at the source rather than scavenging after the fact.
• Mitochondrial membrane potential preservation — Preserves ΔΨ_m, the proton gradient that drives ATP synthase. Relevant in ischemia-reperfusion, where ΔΨ_m collapse triggers mitochondrial permeability transition pore opening and apoptosis (Zhao et al., J Biol Chem 2004; PMID 15178689).
• Anti-apoptotic signaling — Reduced cytochrome c release (secondary to preserved cardiolipin integrity) reduces apoptotic cascade activation in stressed cells.
• No receptor-mediated effects — SS-31 does not bind cell-surface receptors, nuclear receptors, or enzyme active sites at pharmacological concentrations. This is unusual in the peptide therapeutic space and contributes to its clean off-target safety profile.
• Tissue distribution — Accumulates preferentially in cardiolipin-rich tissues (heart, skeletal muscle, retina, kidney, brain) by design. Low concentration in cardiolipin-poor tissues.
• Pharmacokinetics in humans — Plasma half-life ~2.5 hours after SubQ administration; the cardiolipin-binding pool extends effective tissue residence time substantially. This is why once-daily SubQ dosing is pharmacologically coherent despite the short plasma half-life.

What the Research Shows

SS-31 has the most developed clinical evidence base of any community-used peptide after the first-line approved drugs (GLP-1 agonists, TRT, sermorelin). It has been studied in multiple Phase 2 programs in addition to the Barth syndrome pivotal trials.

• Szeto-Schiller peptide design (Szeto, 2006, AAPS J; PMID 16796378) — Foundational design paper establishing the SS-peptide family and the cardiolipin-targeting mechanism.
• Cardiolipin binding mechanism (Birk et al., JASN 2013; PMID 23813215) — Demonstration that SS-31 re-energizes ischemic mitochondria by interacting with cardiolipin.
• TAZPOWER Phase 2/3 Barth syndrome, 28-week randomized portion (Thompson et al., Genet Med 2021; PMID 33129823) — Initial randomized placebo-controlled phase in 12 patients; primary endpoint missed at 28 weeks but set up the open-label extension.
• TAZPOWER 168-week extension (Thompson et al., Genet Med 2024; PMID 38602181) — 8 patients reached 168 weeks. 6-minute walk distance improved by ~95.9 m vs baseline; improvements in Barth Syndrome Symptom Assessment fatigue score and muscle strength. Basis for FDA accelerated approval.
• Heart failure — PROGRESS-HF Phase 2 (Daubert et al., Circ Heart Fail 2017; PMID 29217757) — Phase 2 in HFpEF. Signals on exercise capacity and mitochondrial function at some endpoints; mixed overall primary outcome.
• Heart failure — canine HF (Sabbah et al., Circ Heart Fail 2016; PMID 26839394) — Improved LV and mitochondrial function in dogs with advanced HF. Foundational preclinical cardiac data.
• Primary mitochondrial myopathy — Phase 1 crossover (Karaa et al., Neurology 2018; PMID 29523644) — Dose-escalation, single-dose pharmacodynamic evidence of 6-minute walk improvement.
• Primary mitochondrial myopathy — MMPOWER-3 Phase 3 — Failed primary endpoint at 48 weeks in general primary mitochondrial myopathy; subgroup signals contributed to pivot toward Barth-specific development.
• EMBRACE-STEMI (ST-elevation MI) — Phase 2 in STEMI. Missed primary endpoint on infarct size by MRI but generated mechanistic learning about cardiolipin dynamics in acute ischemia-reperfusion (Brown et al., J Cardiovasc Pharmacol Ther 2014).
• ReCLAIM dry AMD — Phase 2 in dry age-related macular degeneration; functional visual endpoint improvement in subsets.
• Aged muscle fatigue (Roshanravan et al., PLoS One 2021) — Single-dose elamipretide improved in-vivo mitochondrial ATP production in older adult skeletal muscle in a randomized study.
• Aged kidney (Sweetwyne et al., Kidney Int 2017; PMID 28063595) — SS-31 rescued age-related glomerular architecture changes in aged mice. Preclinical support for mitochondrial-related chronic-kidney-disease applications.
• Human failing heart ex vivo (Chatfield et al., JACC Basic Transl Sci 2019) — Improved mitochondrial function in ex-vivo tissue from failing human hearts. Direct human cardiac mechanistic confirmation.
• Barth-syndrome mouse model mitophagy (Sci Rep 2024; DOI 10.1038/s41598-024-64368-y) — SS-31 ameliorates cardiac mitochondrial morphology and defective mitophagy in a Barth syndrome murine model.

Human Data

SS-31 / elamipretide has one of the deepest human trial records of any peptide in this database:

• Phase 1 PK/safety (multiple) — Established pharmacokinetics, once-daily SubQ dosing, clean safety profile. Urva and Stealth BioTherapeutics publications.
• TAZPOWER (NCT03098797) — Barth syndrome, 28 weeks placebo-controlled + 168 weeks open-label. Basis for FDA accelerated approval in September 2025.
• MMPOWER-3 — Primary mitochondrial myopathy Phase 3. Failed primary endpoint at 48 weeks.
• EMBRACE-STEMI — Acute STEMI Phase 2. Primary endpoint missed; mechanistic substudies informative.
• PROGRESS-HF — HFpEF Phase 2. Mixed results; exploratory signals on exercise tolerance.
• ReCLAIM-1, ReCLAIM-2 — Phase 2 dry AMD studies. Some functional visual endpoint improvement.
• Leber hereditary optic neuropathy (LHON) — Exploratory and compassionate-use cases described.
• Aged-muscle fatigue (Roshanravan et al., 2021) — Randomized study in aged adults showing improved in-vivo mitochondrial ATP production.
• Forzinity accelerated approval (September 2025) — FDA accelerated approval based on TAZPOWER extension under Stealth BioTherapeutics.
• Ongoing Phase 3 commitments — Post-accelerated-approval confirmatory commitments apply per FDA accelerated approval framework.

Dosing from the Literature

The Forzinity approved dose provides the gold-standard reference; off-label community practice generally mirrors or reduces from it.

Reconstitution & Storage

Forzinity branded product is supplied as a pre-mixed aqueous solution in single-patient-use vials. Research-chemical SS-31 is typically supplied as lyophilized powder in 10 mg or 40 mg vials.

• Reconstitution (research vial) — Inject BAC water slowly down the vial wall at 45°. Swirl gently; do not shake. Clear colorless solution.
• Storage — Unreconstituted lyophilized powder: 2–8°C preferred. Reconstituted solution: 2–8°C, use within 21–28 days. Do not freeze reconstituted peptide.
• Injection sites — SubQ into abdomen (2" from navel) or thigh. Rotate sites.
• Timing — Once daily at a consistent time. No strong rationale for AM vs PM. Most TAZPOWER patients dosed in the morning.
• Inspection — Discard if cloudy, discolored, or contaminated.

→ Use the Kalios Peptide Calculator for exact syringe units

Side Effects & Risks

SS-31's safety profile across the Phase 2/3 program is among the cleanest of any peptide therapeutic. FDA approval is a strong risk-benefit signal.

• Injection-site reactions — Most common. Mild erythema, tenderness, occasional pruritus. Self-limited.
• Headache — Mild, transient; reported in clinical trials.
• GI discomfort (occasional) — Mild nausea, particularly with the first few doses.
• Fatigue (paradoxical in a subset) — A small proportion of users report initial fatigue, possibly reflecting metabolic adjustment.
• No cardiovascular / hematologic / hepatic / renal signals — Across the Phase 2/3 database including Forzinity pivotal approval, no consistent signals in these domains.
• Immunogenicity — As a tetrapeptide, SS-31 has low immunogenicity. Antibody formation has not been a clinically significant concern.
• Drug interactions — Minimal documented. No CYP450 interactions expected (peptide metabolized by peptidases, not hepatic oxidation).
• Pregnancy / lactation — Not studied; avoid.
• Pediatric use — Approved in Barth syndrome, which often presents in childhood. Label includes pediatric dosing.
• Long-term (168-week TAZPOWER extension) — No unexpected long-term safety signals emerged. One of the longer-duration peptide safety datasets available.
• Purity (gray-market research-chemical supply) — Research-chemical SS-31 varies in quality. The Dmt residue is a synthesis-demanding step and purity problems have been documented in low-tier supply. Third-party HPLC + mass spec certificates of analysis are the minimum bar.
• WADA status — Not specifically named on the WADA Prohibited List. Athletes should consult their federation given broad umbrella categories around metabolic modulators.

Bloodwork & Monitoring

Monitoring in the approved context follows the Forzinity label. For off-label research use:

• Baseline CMP / CBC — Standard.
• Cardiac markers (BNP, troponin) if applicable — Relevant for users with heart failure or cardiomyopathy.
• Lipid panel — Baseline and annually.
• Cardiolipin analysis (specialty lab) — Monolysocardiolipin:cardiolipin ratio is the Barth syndrome biomarker; available at specialty labs.
• 6-minute walk test — The TAZPOWER functional primary endpoint. Baseline and every 3–6 months.
• Cardiac imaging — Echo or cardiac MRI in users with cardiomyopathy; annually or as clinically indicated.
• Fatigue scales — Barth Syndrome Symptom Assessment or equivalent validated instrument.
• Muscle strength — Grip strength, 1-RM, or equivalent objective measure at baseline and periodic recheck.
• Retinal imaging if dry AMD — Fundus photography, OCT.

Supportive Nutrition & Adjuncts

Mitochondrial function is systems-level. SS-31 provides cardiolipin-specific support; broader mitochondrial biology depends on additional inputs.

• CoQ10 (ubiquinol preferred, 100–300 mg) — Electron-transport-chain cofactor; mechanistically complementary to SS-31's cristae-preservation effect.
• L-carnitine (1–2 g) — Fatty-acid shuttle into mitochondria; supports substrate delivery to SS-31-preserved mitochondria.
• Alpha-lipoic acid (300–600 mg) — PDH cofactor and mitochondrial antioxidant.
• PQQ (20 mg) — Mitochondrial biogenesis cofactor; complementary.
• Creatine monohydrate (3–5 g) — ATP buffering; supports cellular energetics.
• Omega-3 (2–3 g EPA/DHA) — Cardiolipin contains multiple unsaturated fatty acids; dietary PUFA supports cardiolipin composition.
• Vitamin D (target 40–60 ng/mL) — General supportive.
• Magnesium (300–400 mg) — ATP cofactor; broad mitochondrial support.
• NAD+ precursors (NR, NMN) — Different mechanism (sirtuin cofactor supply); often combined in mitochondrial-optimization protocols.
• Exercise (aerobic + resistance) — Strongest behavioral input for mitochondrial function. Complements SS-31.
• Things to avoid — Chronic alcohol (mitochondrial toxin), chronic sleep restriction (impairs mitochondrial recovery), known mitochondrial toxins (some antibiotics, high-dose statins in susceptible individuals, doxorubicin chemotherapy).

What to Expect — Timeline

Individual response varies. The TAZPOWER 168-week extension provides the clearest long-duration human benchmark.

• Week 1–2 — Subtle. Some users report mild injection-site reactions and occasional fatigue; others no subjective change.
• Week 3–6 — Earliest reports of subjective improvement in energy, exercise recovery, or reduced perceived fatigue. Objective endpoints not yet measurable.
• Week 6–12 (TAZPOWER 28-week primary analysis) — The 28-week TAZPOWER primary endpoint was not met in randomized comparison; subjective reports of energy improvement accumulate.
• Month 3–6 — Measurable functional improvements emerge in responders. TAZPOWER OLE 6-min walk improvement at 36 weeks was 95.9 m in Barth patients.
• Month 6–12 — Sustained functional improvement in responders. Cardiac stroke volume changes in Barth patients documented.
• Year 2–3 (168-week TAZPOWER extension) — Long-term sustained benefit in the subset that responded and continued. One of the longest-duration peptide therapeutic datasets available.
• Non-responders — Real. MMPOWER-3 failed primary endpoint at 48 weeks in general mitochondrial myopathy. Cardiolipin-specific pathology (Barth) is where SS-31 works best.
• Discontinuation — Benefits reportedly attenuate over weeks after cessation. Cardiolipin tissue binding extends effective duration but not indefinitely.
• Off-label general anti-aging — Evidence is observational / extrapolated. Expect modest objective effects at best.
• If you feel worse — Persistent injection site issues, new cardiac symptoms, sustained fatigue. Stop and evaluate.

Practical User Notes

• Barth syndrome → pursue Forzinity through prescription — The approved indication. Don't substitute gray-market for branded product in a rare-disease context where product quality matters.
• Off-label use → start 10–20 mg daily — Assess response at 4–8 weeks. Escalate to 40 mg if needed.
• Consistent daily timing — Once daily at a fixed time; no strong AM/PM preference.
• Combine with complementary mitochondrial support — CoQ10, creatine, omega-3, exercise. SS-31 is not a standalone mitochondrial fix.
• Track objectively — 6-min walk test, VO2max, subjective fatigue scale. Subjective reports are unreliable for gradual changes.
• Consider stacking with NAD+ precursor — Different mechanism; common combination in mitochondrial-optimization protocols.
• Don't confuse SS-31 response with training or sleep effects — Lifestyle improvements can produce subjective changes similar to SS-31; controlled comparison is hard.
• Injection technique — 29–31G insulin syringe, SubQ 45° into abdomen or thigh. Rotate sites.
• Sourcing — Branded Forzinity for Barth patients. Research-chemical SS-31 with third-party HPLC + mass spec + Dmt-residue-confirmation testing for off-label use.
• Storage — 2–8°C refrigerated for reconstituted product; use within 28 days.
• Honest expectations — Even in the approved indication (Barth), SS-31 improves symptoms meaningfully but does not cure the underlying TAFAZZIN defect. For off-label aging or mitochondrial-adjacent conditions, expect modest objective changes rather than dramatic transformation.
• Red flags to stop — Persistent injection-site problems, new cardiac symptoms, severe GI, any new unexplained symptom. Cessation first, evaluation second.

Commonly Stacked With

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Regulatory Status

Related Compounds

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Key References

1. Szeto HH. Cell-permeable, mitochondrial-targeted, peptide antioxidants. AAPS J. 2006;8(2):E277-E283. PMID: 16796378.
2. Zhao K, Zhao GM, Wu D, Soong Y, Birk AV, Schiller PW, Szeto HH. Cell-permeable peptide antioxidants targeted to inner mitochondrial membrane inhibit mitochondrial swelling, oxidative cell death, and reperfusion injury. J Biol Chem. 2004;279(33):34682-34690. PMID: 15178689.
3. Birk AV, Liu S, Soong Y, Mills W, Singh P, Warren JD, Seshan SV, Pardee JD, Szeto HH. The mitochondrial-targeted compound SS-31 re-energizes ischemic mitochondria by interacting with cardiolipin. J Am Soc Nephrol. 2013;24(8):1250-1261. PMID: 23813215.
4. Thompson WR, Hornby B, Manuel R, Bradley E, Laux J, Carr J, Vernon HJ. A phase 2/3 randomized clinical trial followed by an open-label extension to evaluate the effectiveness of elamipretide in Barth syndrome. Genet Med. 2021;23(3):471-478. PMID: 33129823.
5. Thompson WR, Manuel R, Abbruscato A, Carr J, Campbell J, Hornby B, Vaz FM, Vernon HJ. Long-term efficacy and safety of elamipretide in patients with Barth syndrome: 168-week open-label extension results of TAZPOWER. Genet Med. 2024;26(7). PMID: 38602181.
6. Sabbah HN, Gupta RC, Kohli S, Wang M, Hachem S, Zhang K. Chronic Therapy With Elamipretide (MTP-131), a Novel Mitochondria-Targeting Peptide, Improves Left Ventricular and Mitochondrial Function in Dogs With Advanced Heart Failure. Circ Heart Fail. 2016;9(2):e002206. PMID: 26839394.
7. Daubert MA, Yow E, Dunn G, Marchev S, Barnhart H, Douglas PS, O'Connor C, Goldstein S, Udelson JE, Sabbah HN. Novel Mitochondria-Targeting Peptide in Heart Failure Treatment: A Randomized, Placebo-Controlled Trial of Elamipretide. Circ Heart Fail. 2017;10(12):e004389. PMID: 29217757.
8. Karaa A, Haas R, Goldstein A, Vockley J, Weaver WD, Cohen BH. Randomized dose-escalation trial of elamipretide in adults with primary mitochondrial myopathy. Neurology. 2018;90(14):e1212-e1221. PMID: 29523644.
9. Roshanravan B, Liu SZ, Ali AS, Shankland EG, Goss C, Amory JK, Robertson HT, Marcinek DJ, Conley KE. In vivo mitochondrial ATP production is improved in older adult skeletal muscle after a single dose of elamipretide in a randomized trial. PLoS One. 2021;16(7):e0253849.
10. Chatfield KC, Sparagna GC, Chau S, Phillips EK, Ambardekar AV, Aftab M, Mitchell MB, Sucharov CC, Miyamoto SD, Stauffer BL. Elamipretide Improves Mitochondrial Function in the Failing Human Heart. JACC Basic Transl Sci. 2019;4(2):147-157.
11. Sweetwyne MT, Pippin JW, Eng DG, Hudkins KL, Chiao YA, Campbell MD, Marcinek DJ, Alpers CE, Szeto HH, Rabinovitch PS, Shankland SJ. The mitochondrial-targeted peptide, SS-31, improves glomerular architecture in mice of advanced age. Kidney Int. 2017;91(5):1126-1145. PMID: 28063595.
12. Szeto HH, Birk AV. Serendipity and the discovery of novel compounds that restore mitochondrial plasticity. Clin Pharmacol Ther. 2014;96(6):672-683. PMID: 25188725.
13. ClinicalTrials.gov. A Trial to Evaluate Safety, Tolerability, and Efficacy of Elamipretide in Subjects with Barth Syndrome (TAZPOWER). NCT03098797.
14. Stealth BioTherapeutics. FORZINITY (elamipretide) prescribing information. FDA accelerated approval September 2025.
15. Brown DA, Hale SL, Baines CP, et al. Reduction of early reperfusion injury with the mitochondria-targeting peptide bendavia. J Cardiovasc Pharmacol Ther. 2014;19(1):121-132.
16. SS-31 treatment ameliorates cardiac mitochondrial morphology and defective mitophagy in a murine model of Barth syndrome. Sci Rep. 2024;14:s41598-024-64368-y.