what is the difference
SS-31 and elamipretide
Two names, two registry counts, and one molecule underneath both of them, with a trial history that is unusually complete and unusually easy to misread.
SS-31 and elamipretide are the same substance: a four amino acid aromatic-cationic peptide that concentrates in the inner membrane of the mitochondrion, where it associates with cardiolipin, the lipid that gives that membrane its shape. The molecule has also carried the development codes MTP-131 and Bendavia, and since 19 September 2025 it has a brand name, Forzinity, under application 215244 [6].
The names split the public record in two. On 2 August 2026 ClinicalTrials.gov returned 21 registrations for elamipretide and 2 for SS-31 [7]. Those are two indexes of one drug, not two programmes, and adding them together produces a trial count nobody ran. The published half of that record is the part worth reading closely, because it is both large and, at the primary endpoint, consistently negative.
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This page reports what has been documented about a compound. It is not medical advice, not a diagnosis, not a dosing protocol, and not a recommendation to obtain or use anything described here. Talk to a licensed clinician about anything concerning your health. Read the full disclaimer.
Reviewed against editorial standards Updated
The short answer
One molecule, two names. Elamipretide is the international nonproprietary name and the one the sponsor's trials were registered under; SS-31 is the older laboratory designation, and it is the name the compound is sold under outside the approved product. FDA granted accelerated approval on 19 September 2025 as Forzinity, to improve muscle strength in patients with Barth syndrome weighing at least 30 kg [6]. That approval covers one rare genetic condition and rests on the open-label extension of a trial whose randomized phase missed both of its primary endpoints [1] [2].
Side by side
| Property | SS-31 | Elamipretide |
|---|---|---|
| What it is | A four amino acid aromatic-cationic peptide that concentrates in the inner mitochondrial membrane | The same four amino acid peptide, under its international nonproprietary name |
| Other names it carries | Also written SS31 and SS-31 peptide | MTP-131, Bendavia, and since 2025 the brand name Forzinity |
| Registrations on ClinicalTrials.gov | 2 on a term search, run 2 August 2026 [7] | 21 on a term search, run the same day [7] |
| What the two counts mean together | Two indexes of one drug. They describe the same programme and are not additive | Same. A study registered under one name is the same study under the other |
| Approval status | The research name carries no approval of its own | Accelerated approval granted by FDA on 19 September 2025 as Forzinity, application 215244, to improve muscle strength in patients with Barth syndrome weighing at least 30 kg [6] |
| Randomized results | Part 1 of TAZPOWER, a placebo-controlled crossover in 12 subjects, met neither primary endpoint [1]. MMPOWER-3, a phase 3 in 218 participants, is recorded as terminated, with a registry stop reason reading that the double blind portion did not meet the primary end points [3] [7] | ReCLAIM-2, a phase 2 in dry age-related macular degeneration, 176 patients randomized, missed both primaries [4]. PROGRESS-HF, a phase 2 in heart failure, 71 patients, found no significant difference against placebo on its imaging endpoint [5] |
| What the approval rests on | The open-label extension of the trial whose randomized phase failed, where changes against baseline reached significance at 36 weeks and were followed to 168 weeks [1] [2] | Same |
| Evidence grade on this site | Not graded. A grade is derived from tiered claim rows, and that source review has not been run here | Same. The individual trials are cited by number instead |
| What is missing | A randomized trial of this molecule that met a primary endpoint | Any evidence bearing on ageing, energy or general mitochondrial health, which is what the research name is sold for |
Why the two get mixed up
Development names outlive their programmes. SS-31 came out of the laboratory series it was numbered in, elamipretide is the nonproprietary name assigned later, and Bendavia and MTP-131 belong to the commercial stages in between. All four refer to one substance, and registry search is literal: a study registered as elamipretide does not surface under SS-31 unless someone typed both. That is why the same programme returns two different numbers depending on which name is searched.
The commercial split reinforces it. The approved product carries a brand name and one rare genetic condition, while the same molecule is sold separately under the research designation for purposes no regulator has assessed. A buyer who searches the research name finds a thin registry record and a large mechanistic literature; a reader who searches the nonproprietary name finds a phase 3 programme, several completed trials and an FDA approval. Both are looking at one drug. The shape of that record is the last trap: an approval reads as a verdict on the whole molecule, and the run of missed primary endpoints behind it sits in the body of each paper rather than in its title.
What the published record covers for each
The randomized record is the part of this story most often skipped, so it is worth taking trial by trial. TAZPOWER was a randomized, double-blind, placebo-controlled crossover trial in Barth syndrome: 12 subjects took elamipretide or placebo for 12 weeks, washed out for four weeks, then crossed to the other arm. In that randomized part neither primary endpoint, the six-minute walk test and a Barth syndrome symptom assessment scale, was met [Human RCT] [1]. Ten subjects continued into an open-label extension with no control arm, where changes against baseline reached significance at 36 weeks, and a later report followed the extension to 168 weeks [Human open-label] [1] [2].
MMPOWER-3 was the largest randomized test the molecule faced: a phase 3 in primary mitochondrial myopathy with 218 participants. It is recorded on the registry as terminated, and the registry's own stop reason reads that the double blind portion of the trial did not meet the primary end points [Human RCT] [3] [7]. ReCLAIM-2, a randomized, placebo-controlled, double-masked phase 2 in dry age-related macular degeneration with geographic atrophy, randomized 176 patients and did not reach statistical significance on either primary endpoint, low-luminance visual acuity and the change in atrophy area, though it reported differences on predefined secondary imaging measures [Human RCT] [4]. PROGRESS-HF randomized 71 patients with heart failure and reduced ejection fraction across three arms, and the change in left ventricular end systolic volume at four weeks did not differ significantly from placebo in either active arm [Human RCT] [5].
The regulatory fact sits beside those results rather than on top of them, and it carries a dated document rather than a tier. FDA granted accelerated approval on 19 September 2025 for one rare genetic condition, in patients weighing at least 30 kg, under application 215244 [6]. Accelerated approval is a pathway that permits a decision on a surrogate or intermediate measure with confirmatory evidence to follow, and the reviewed package here included the uncontrolled extension of the trial whose randomized phase missed both primaries [1] [2].
None of the above is evidence about ageing, energy or general mitochondrial health, which are the claims attached to the research name. No registered trial in the set of 21 tested those uses, and a 2026 narrative review of peptides marketed direct to patients places SS-31 among the compounds whose gray-market use runs well ahead of the record [8]. Where the record ends is a fact about the record, not a verdict about the molecule.
Our takeTwo registry counts, one molecule, and a trial history in which every adequately powered randomized test missed its primary endpoint. All of it is on the public record, and none of it is about the uses the research name is sold for.
Frequently asked questions
Are SS-31 and elamipretide the same thing?
Yes. One four amino acid peptide with several names: SS-31 from the laboratory series it was numbered in, elamipretide as its international nonproprietary name, MTP-131 and Bendavia from its development history, and Forzinity as the brand name of the approved product since September 2025 [6].
Why do the two names return different trial counts?
Because registry search matches text. A study registered under elamipretide does not surface under SS-31 unless the record happens to carry both. On 2 August 2026 a term search returned 21 records for elamipretide and 2 for SS-31 [7]. Those are two views of one programme, and adding them would describe 23 trials that were never run.
What is it approved for?
FDA granted accelerated approval on 19 September 2025 under the brand name Forzinity, application 215244, to improve muscle strength in patients with Barth syndrome weighing at least 30 kg [6]. Barth syndrome is a rare genetic condition affecting cardiolipin, the lipid this peptide associates with. The approval says nothing about anyone else, and a regulatory action carries no evidence tier.
Did the randomized trials meet their endpoints?
The randomized ones did not. Part 1 of TAZPOWER, a placebo-controlled crossover in 12 subjects, met neither primary endpoint [1]. MMPOWER-3, a phase 3 in 218 participants, is recorded as terminated with a registry stop reason stating that the double blind portion did not meet the primary end points [3] [7]. ReCLAIM-2, in 176 patients with dry age-related macular degeneration, missed both primaries [4]. PROGRESS-HF, in 71 patients with heart failure, found no significant difference against placebo on its imaging endpoint [5].
Then what did the approval rest on?
The open-label extension of the Barth syndrome trial. Ten of the 12 subjects continued on drug with no control arm, and significant changes against baseline were reported at 36 weeks and followed out to 168 weeks in a smaller group [1] [2]. Accelerated approval is a pathway that permits a decision on a surrogate or intermediate measure with confirmatory evidence to follow, which is why the sequence looks unusual next to a conventional approval.
Does any of this bear on ageing or energy?
Nothing in the registered set tested those uses. The 21 registrations cover Barth syndrome, primary mitochondrial myopathy, ophthalmic conditions, heart failure and related indications [7]. Claims about ageing, energy and general mitochondrial function circulate under the research name and rest on mechanism and on community reports rather than on any trial above. No evidence grade is stated on this page either, because a grade is derived from tiered claim rows and that source review has been run here only for KPV.
References
- Reid Thompson W, 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, a genetic disorder of mitochondrial cardiolipin metabolism. Genet Med. 2021. PMID 33077895 DOI 10.1038/s41436-020-01006-8
- 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. PMID 38602181 DOI 10.1016/j.gim.2024.101138
- Karaa A, Bertini E, Carelli V, Cohen BH, Enns GM, Falk MJ, Goldstein A, Gorman GS, Haas R, Hirano M, Klopstock T, Koenig MK, Kornblum C, Lamperti C, Lehman A, Longo N, Molnar MJ, Parikh S, Phan H, Pitceathly RDS, Saneto R, Scaglia F, Servidei S, Tarnopolsky M, Toscano A, Van Hove JLK, Vissing J, Vockley J, Finman JS, Brown DA, Shiffer JA, Mancuso M, MMPOWER-3 Trial Investigators. Efficacy and Safety of Elamipretide in Individuals With Primary Mitochondrial Myopathy: The MMPOWER-3 Randomized Clinical Trial. Neurology. 2023. PMID 37268435 DOI 10.1212/WNL.0000000000207402
- Ehlers JP, Hu A, Boyer D, Cousins SW, Waheed NK, Rosenfeld PJ, Brown D, Kaiser PK, Abbruscato A, Gao G, Heier J, ReCLAIM-2 (SPIAM-202) Study Investigators. ReCLAIM-2: A Randomized Phase II Clinical Trial Evaluating Elamipretide in Age-related Macular Degeneration, Geographic Atrophy Growth, Visual Function, and Ellipsoid Zone Preservation. Ophthalmol Sci. 2025. PMID 39605874 DOI 10.1016/j.xops.2024.100628
- Butler J, Khan MS, Anker SD, Fonarow GC, Kim RJ, Nodari S, O'Connor CM, Pieske B, Pieske-Kraigher E, Sabbah HN, Senni M, Voors AA, Udelson JE, Carr J, Gheorghiade M, Filippatos G. Effects of Elamipretide on Left Ventricular Function in Patients With Heart Failure With Reduced Ejection Fraction: The PROGRESS-HF Phase 2 Trial. J Card Fail. 2020. PMID 32068002 DOI 10.1016/j.cardfail.2020.02.001
- US Food and Drug Administration. Novel drug approvals for 2025. Records Forzinity (elamipretide), approved 19 September 2025 under application 215244, to improve muscle strength in patients with Barth syndrome weighing at least 30 kg. FDA, Center for Drug Evaluation and Research. 2025. Approvals table
- US National Library of Medicine, ClinicalTrials.gov. Registry searches run through API v2 on 2 August 2026: a term search for elamipretide returned 21 records and a term search for SS-31 returned 2, describing one molecule indexed under two names. The record for NCT03323749, MMPOWER-3, carries overall status terminated and the stop reason: Part1,double blind portion of the trial did not meet the primary end points. ClinicalTrials.gov. 2026. Registry record
- Mendias CL, Awan TM. Safety and Efficacy of Approved and Unapproved Peptide Therapies for Musculoskeletal Injuries and Athletic Performance. Sports Med. 2026. PMID 41966639 DOI 10.1007/s40279-026-02437-0