Reviewed & approved by Dr. Nova Reyes · Last checked 2026-10-15. ← Back to Evidence Library
SS-31 (elamipretide): what the evidence says
At a glance
What it is: a lab-made 4-amino-acid peptide that travels to mitochondria (the cell's energy-making parts) and binds cardiolipin, a fat in their inner membrane. Its official name is elamipretide. It was first described as "SS-31" (Szeto-Schiller peptide 31) and is developed by Stealth BioTherapeutics. Gray-market "SS-31" vials are sold for energy, endurance, anti-aging and "mitochondrial health." R1, R2
What the evidence says: in Barth syndrome, a 12-person placebo-controlled trial missed both of its main goals. Walking distance and symptoms improved later, when everyone took the drug openly with no placebo group. FDA's approval rests on muscle strength, an in-between measure. In other diseases, a 218-person phase 3 trial (large studies confirming benefit and safety before approval) in mitochondrial muscle disease found no benefit, and trials in heart failure, dry macular degeneration and an inherited eye disease missed their main goals. Nothing has been tested in healthy people. R3–R8
Biggest risks: injection-site reactions in nearly everyone, rises in a type of white blood cell (eosinophils), and serious allergic reactions listed as a warning on the label. Plus not knowing what's in the vial. R10
| Claim | Rating |
|---|---|
| Human Barth syndrome (approved Forzinity) | Very limited (mixed results): one 12-person placebo-controlled crossover trial missed both main goals; improvements came in an open-label extension (8–10 people). Stealth-funded staff among the authors R3, R4 |
| Human Primary mitochondrial myopathy (muscle disease) | Very limited (mixed results): one 218-person phase 3 placebo-controlled trial found no improvement in walking or fatigue; a planned subgroup and later unplanned analyses suggested possible benefit in some genetic groups; Stealth-sponsored R5, R20 |
| Human Heart failure with reduced pumping | Very limited (mixed results): one short 71-person phase 2 trial (mid-size studies testing doses and early effects); no improvement in heart size or pumping; Stealth author R6 |
| Human Dry age-related macular degeneration | Very limited (mixed results): one 176-person phase 2 trial missed both main goals; some retina-imaging measures looked better; Stealth authors R7 |
| Human Leber hereditary optic neuropathy (eye drops) | Very limited (mixed results): one 12-person trial; vision did not improve vs placebo drops (main goal missed); some unplanned visual-field results looked better R8 |
| Animal Energy, endurance, anti-aging, "mitochondrial health" in healthy people (gray-market use) | No human data (animal/lab only) R9 |
| Regulatory | US: accelerated approval (Forzinity), Barth syndrome only, Sept 19, 2025 · not authorised in the EU (EU orphan designations only) · 503A: not in any category · 503B: not nominated · WADA 2026: not named; The Open Peptide Project's reading is that it is not prohibited, not a WADA ruling R10–R19 |
| Established human dose | Only the Forzinity label, for Barth syndrome. Unknown None for any other use |
Evidence verdict: Barth syndrome: Very limited (mixed results) · Mitochondrial myopathy: Very limited (mixed results) · Heart failure: Very limited (mixed results) · Dry macular degeneration: Very limited (mixed results) · Leber hereditary optic neuropathy: Very limited (mixed results) · Energy, endurance and anti-aging in healthy people: No human data (animal/lab only) Card verdict: Very limited (Barth syndrome, FDA accelerated approval; heart failure, myopathy, eye diseases: mixed results) · Energy, endurance, anti-aging in healthy people: No human data Card note: Varies by use, see page
This page reports what studies used. It is not dosing advice.
Legend: HUMAN data · ANIMAL / LAB data · UNKNOWN · UNVERIFIED: not yet confirmed against a primary source
What "No human data" means here: for energy, endurance, anti-aging or "mitochondrial health" in healthy people, there are animal and lab studies only, and no human trials.
What is it?
In Barth syndrome, a faulty gene leaves cardiolipin abnormal, so mitochondria make energy poorly. Elamipretide is meant to stabilize cardiolipin and help mitochondria work. Changes in cardiolipin levels, retina scans, or heart-imaging numbers are lab or imaging measures, not health benefits by themselves. What matters is whether people walk, see, breathe and feel better, which is what most of the trials below tested. R1, R2
The approved product vs. the gray-market vial: Forzinity is a prescription solution for injection, made under FDA oversight; product details are in the FDA label. A gray-market "SS-31" vial is not the approved product. R10
Does it work?
Human Barth syndrome (approval evidence; this does not apply to gray-market use): - TAZPOWER, Thompson 2021: a phase 2/3 double-blind crossover trial. 12 people took elamipretide and placebo in turn (schedule in the study table). Neither main goal was met (6-minute walk, symptom score). In the open-label part, where everyone took the drug and there was no placebo group, 6-minute walk rose by 95.9 m and symptoms improved at 36 weeks (8 people reached that point). According to the label, 10 of the 12 completed the placebo-controlled part. One author is a Stealth employee. R3, R10 - 168-week extension, Thompson 2024: 10 people entered, 8 reached week 168. Walking gains and some heart-imaging measures held up. Still no placebo group. Three authors are Stealth employees; two received Stealth research support. R4 - FDA's view: in its May 15, 2025 complete response letter, FDA could not conclude the drug works from the goals proposed, and also cited a manufacturing-facility problem. In the second review, FDA's clinical and statistical reviewers still recommended against approval; the senior official who signs the decision approved it, accepting more uncertainty because the disease is very rare and has no other treatment. After resubmission, FDA granted accelerated approval based on knee-extensor muscle strength, "an intermediate clinical endpoint." Continued approval "may be contingent upon verification and description of clinical benefit in a confirmatory trial," and FDA requires a new randomized, placebo-controlled trial. R11, R12, R14
Human Primary mitochondrial myopathy: MMPOWER-3, Karaa 2023, 218 adults (109 per group), the largest trial (schedule in the study table). No improvement in 6-minute walk (difference −3.2 m, p = 0.69) or fatigue (p = 0.37) vs placebo. Sponsored by Stealth; one author a Stealth employee and many investigators report Stealth funding. A planned subgroup with nuclear-DNA gene changes did better on walking; later unplanned analyses pointed to one genetic group (mtDNA maintenance or "replisome" disorders), and Stealth designed a new phase 3 trial (NuPOWER) around it. Subgroup findings can only suggest new trials, not show a benefit. R5, R20
Human Heart failure: PROGRESS-HF, Butler 2020, 71 patients with weakened heart pumping, two strengths vs placebo (schedule in the study table). Heart size and pumping on MRI did not improve. One author is from Stealth. R6
Human Dry age-related macular degeneration: ReCLAIM-2, Ehlers 2025, 176 patients (117 drug, 59 placebo; schedule in the study table). Both main goals were missed (low-light vision, size of the damaged area). A retina-imaging measure (ellipsoid zone loss) slowed, and more people gained 10 or more letters in low-light vision (14.6% vs 2.1%; these "nominal" p-values were not part of the main test, so they could have been chance). Two authors are Stealth employees. Stealth plans phase 3 trials using the imaging measure. R7, R2
Human Leber hereditary optic neuropathy: Karanjia 2024, 12 patients, eye drops vs vehicle drops (schedule in the study table). Vision did not improve more than in placebo-treated eyes (the main goal). Half the patients met the authors' criteria for a meaningful benefit, and an unplanned visual-field analysis looked better, but neither is a controlled result. Caution [UNVERIFIED: funding and conflict statements not read (no free full text)] R8
Animal Animals and lab: aging, heart, kidney, brain and muscle models. Not reviewed in detail for this page. R9
Who paid / conflicts: Stealth BioTherapeutics sponsored MMPOWER-3 and funded ReCLAIM-2 (and took part in its design, analysis and writing), and Stealth employees co-authored the Barth, MMPOWER-3, PROGRESS-HF and ReCLAIM-2 papers. Caution [UNVERIFIED: funding statements for PROGRESS-HF and the LHON trial not read (no free full text)] R3–R8
Is it safe?
- Human Forzinity label (Barth crossover trial, 12 people): injection-site reactions in all 12 on drug vs 8 of 12 on placebo. Absolute eosinophil counts rose often with use of 30 days or more, peaking around 90 days and returning to baseline after 6 to 12 months or after stopping, without symptoms. Warnings: serious allergic reactions, and benzyl alcohol in the product, which can be toxic to newborns (it is not approved in newborns). R10
- Human Other trials: MMPOWER-3 reported mostly mild to moderate adverse events (problems reported after use, which may or may not have been caused by the drug). In ReCLAIM-2, adverse events occurred in 86% on drug vs 71% on placebo, mostly injection-site reactions (itching, pain, bruising, redness). PROGRESS-HF found drug-related adverse events at similar rates in all groups. The eye-drop trial reported no serious adverse events. R5–R8
- Dropouts vs placebo: in TAZPOWER, 10 of 12 completed the placebo-controlled part and continued into the extension (label), and 8 reached 36 weeks; Caution [UNVERIFIED: dropouts by group not checked for MMPOWER-3, PROGRESS-HF or ReCLAIM-2; abstracts only] R3, R4
- Half-life (the time it takes for half of the drug to be cleared from the body): about 3 to 4 hours, per FDA's integrated review; the label gives no figure. Almost all of it leaves in the urine within 48 hours. R10, R14
- Unknown Nothing is known about use in healthy people.
Is it legal?
- US (FDA): Forzinity (elamipretide) injection, Stealth BioTherapeutics, NDA 215244, accelerated approval Sept 19, 2025, "to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg." This came after a complete response letter on May 15, 2025 and resubmission on Aug 15, 2025. A rare pediatric disease priority review voucher was announced in the Federal Register on Dec 19, 2025. We found no withdrawal or conversion to traditional approval as of Oct 15, 2026. R10–R15
- EU: not authorised. EMA lists positive orphan designations for elamipretide in Barth syndrome (EU/3/21/2430, May 20, 2021) and myopathic mitochondrial DNA depletion syndrome (EU/3/22/2614, May 16, 2022). An orphan designation gives incentives to develop drugs for rare diseases; it is not an approval. R16
- Other countries: Caution [UNVERIFIED: no regulator outside the US and EU checked]
- Compounding (503A/503B): no entry for elamipretide or SS-31 in any category of the 503A nominations list (updated May 14, 2026), the 503B nominations list (updated Mar 21, 2025) or FDA's "significant safety risks" page (content current Apr 22, 2026). R17, R18
- Athletes: WADA's 2026 list does not name elamipretide or SS-31. Unknown The Open Peptide Project's reading (not a WADA ruling): because it is approved by FDA, S0 ("non-approved substances") does not apply, and we found no other section covering it. Athletes should ask their anti-doping organization. R19
What's in the vial?
Forzinity (FDA label on DailyMed) is the only approved product R10, R13. A gray-market "SS-31" vial is not the approved product. It has no quality control and no guarantee of identity. It could contain the wrong compound, the wrong amount, impurities or bacterial toxins, or be fake (counterfeit). The trial results above don't transfer to it. We test retail vials blind under the Open Peptide Standard. See results at /tests/. A passing test covers one batch, tested on one date. It does not mean the compound itself is safe.
What do users report?
Self-report, not evidence.
We haven't summarized user reports for this peptide yet.
Study details
R3–R8 Human Human studies
| Study | People | Route | Dose used (study arm, not a recommendation) | Follow-up | Reported | Side effects / dropouts | Limitations | Citation |
|---|---|---|---|---|---|---|---|---|
| TAZPOWER part 1 (Thompson 2021, phase 2/3) | 12 with Barth syndrome | Subcutaneous, crossover | 40 mg once daily or placebo for 12 weeks, 4-week washout, then 12 weeks of the other | 28 wk | Both primary endpoints missed | Label: local injection-site reactions 12/12 on drug vs 8/12 on placebo; 10 of 12 completed the crossover | 12 people | PMID 33077895 |
| TAZPOWER extension (Thompson 2021, 2024) | 10 entered, 8 to wk 168 | Subcutaneous, open-label | 40 mg once daily | 168 wk | 6MWT +95.9 m (36 wk), +96.1 m (168 wk) | Injection-site reactions most common; 2 of 10 did not reach wk 168 | No placebo; Stealth authors | PMID 33077895; PMID 38602181 |
| MMPOWER-3 (Karaa 2023, phase 3) | 218 with primary mitochondrial myopathy (109 vs 109) | Subcutaneous | 40 mg once daily or placebo for 24 weeks | 24 wk | 6MWT −3.2 m vs placebo (p=0.69); fatigue p=0.37 | Mostly mild to moderate adverse events; dropouts by group UNVERIFIED | Stealth-sponsored | PMID 37268435; NCT03323749 |
| PROGRESS-HF (Butler 2020, phase 2) | 71 with HFrEF | Subcutaneous | 4 mg or 40 mg once daily, or placebo, for 28 days | 4 wk | No change in LVESV or LVEF vs placebo | Drug-related adverse events similar across groups; dropouts by group UNVERIFIED | Short; imaging endpoint | PMID 32068002 |
| ReCLAIM-2 (Ehlers 2025, phase 2) | 176 with dry AMD + geographic atrophy (117 vs 59) | Subcutaneous | 40 mg once daily or placebo for 48 weeks | 52 wk | Primary endpoints missed; EZ loss slowed (nominal P=0.0034) | Adverse events 86% vs 71%, mostly injection-site reactions; dropouts by group UNVERIFIED | Surrogate secondary measures; Stealth authors | PMID 39605874; NCT03891875 |
| Karanjia 2024 (phase 2) | 12 with LHON | Eye drops | 1% topical solution in one or both eyes vs vehicle for 52 weeks, then open-label up to 108 more weeks; drops per day UNVERIFIED | Up to 160 wk | BCVA not different vs vehicle | Mostly mild to moderate, self-resolving; no serious adverse events; dropouts UNVERIFIED | 12 people | PMID 37923251 |
R10–R19 Regulatory sources (as of Oct 15, 2026)
- R10 Forzinity label, DailyMed (Stealth BioTherapeutics; label effective Dec 10, 2025): https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=146bf34c-76f2-48db-ac07-fb29cce2cd75
- R11 FDA press release, Sept 19, 2025: https://www.fda.gov/news-events/press-announcements/fda-grants-accelerated-approval-first-treatment-barth-syndrome
- R12 FDA approval letter, NDA 215244: https://www.accessdata.fda.gov/drugsatfda_docs/appletter/2025/215244Orig1s000ltr.pdf
- R13 Drugs@FDA, NDA 215244: https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm?event=overview.process&ApplNo=215244
- R14 FDA integrated review (includes the May 15, 2025 complete response): https://www.accessdata.fda.gov/drugsatfda_docs/nda/2025/215244Orig1s000IntegratedR.pdf
- R15 Federal Register 2025-23409, priority review voucher (Dec 19, 2025): https://www.federalregister.gov/documents/2025/12/19/2025-23409/issuance-of-priority-review-voucher-rare-pediatric-disease-product-forzinity-elamipretide
- R16 EMA medicines and orphan designations data (downloaded Oct 15, 2026): https://www.ema.europa.eu/en/documents/report/medicines-output-medicines_json-report_en.json ; https://www.ema.europa.eu/en/documents/report/medicines-output-orphan_designations-json-report_en.json
- R17 FDA 503A nominations list (May 14, 2026): https://www.fda.gov/media/94155/download ; FDA "significant safety risks" page: https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks
- R18 FDA 503B nominations list (Mar 21, 2025): https://www.fda.gov/media/94164/download
- R19 WADA 2026 Prohibited List: https://www.wada-ama.org/en/resources/world-anti-doping-code-and-international-standards/prohibited-list
Full reference list (PMIDs verified on PubMed, Oct 15, 2026)
- R1 Tung C, et al. Int J Mol Sci. 2025;26(3):944. doi:10.3390/ijms26030944. PMID 39940712 (review).
- R2 Shirley M. Drugs. 2026;86(3):377-383. doi:10.1007/s40265-025-02269-8. PMID 41335372 (review; manufacturer offered comment during peer review).
- R3 Reid Thompson W, et al. Genet Med. 2021;23(3):471-478. doi:10.1038/s41436-020-01006-8. PMID 33077895. Carr is a Stealth employee.
- R4 Thompson WR, et al. Genet Med. 2024;26(7):101138. doi:10.1016/j.gim.2024.101138. PMID 38602181. Abbruscato, Campbell and Carr are Stealth employees; Vernon and Vaz received Stealth research support.
- R5 Karaa A, et al. Neurology. 2023;101(3):e238-e252. doi:10.1212/WNL.0000000000207402. PMID 37268435. Brown is a Stealth employee; most investigators report Stealth funding; NCATS and MRC grants listed on PubMed.
- R6 Butler J, et al. J Card Fail. 2020;26(5):429-437. doi:10.1016/j.cardfail.2020.02.001. PMID 32068002. Carr (Stealth) co-author. Caution [UNVERIFIED: trial funding statement not read]
- R7 Ehlers JP, et al. Ophthalmol Sci. 2025;5(1):100628. doi:10.1016/j.xops.2024.100628. PMID 39605874. Funded by Stealth BioTherapeutics, which took part in design, analysis and writing; Abbruscato and Gao are from Stealth.
- R8 Karanjia R, Sadun AA. Ophthalmology. 2024;131(4):422-433. doi:10.1016/j.ophtha.2023.10.033. PMID 37923251.
- R9 Example of animal work: Vahle B, et al. Circ Heart Fail. 2026;19:e014397. doi:10.1161/CIRCHEARTFAILURE.126.014397. PMID 42290373.
- R20 Karaa A, et al. Orphanet J Rare Dis. 2024;19:431. doi:10.1186/s13023-024-03421-5. PMID 39574155 (post hoc analysis).
Disclaimer
This page is for education and harm reduction. It is not medical advice and not a recommendation to use SS-31 or elamipretide. Please talk to a clinician you trust, especially if you have Barth syndrome or another mitochondrial disease, heart or eye disease, allergies, or are pregnant, or are a tested athlete. Seek care right away for a serious reaction, and report it to FDA MedWatch (https://www.fda.gov/safety/medwatch) or your national regulator.