Elamipretide
Also sold as: SS-31, MTP-131, Bendavia, Forzinity, elamipretide hydrochloride
Elamipretide is FDA-approved, under the brand name FORZINITY (NDA 215244, Stealth BioTherapeutics), but only under accelerated approval granted 19 September 2025 and only for one indication: 'to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg.' The FDA-approved labeling states that in the randomized, double-blind, placebo-controlled trial 'FORZINITY was not superior to placebo on these primary endpoints', and that increases in knee extensor muscle strength 'were not observed during the randomized trial but were observed during the extension period' — the uncontrolled, open-label extension. FDA's own clinical and biostatistical reviewers and Cross-Discipline Team Leader concluded there was 'not substantial evidence of effectiveness on knee muscle strength for accelerated approval' and recommended a Complete Response; the signatory authority overruled them, writing that the decision accepts 'more uncertainty than we would accept for more common diseases' in a disease affecting roughly 150 patients in the United States with no approved treatments. FDA required a randomized, double-blind, placebo-controlled confirmatory trial and stated that if it 'fails to verify clinical benefit or is not conducted with due diligence … we may withdraw this approval.' No FDA approval covers elamipretide, or the same molecule sold as SS-31, for mitochondrial myopathy, heart failure, macular degeneration, athletic performance or anti-aging use.
Which molecule this is. A four-residue mitochondria-targeting peptide. The FDA-approved labeling describes the molecule precisely: 'All amino acid residues in FORZINITY have the L configuration except for arginine which has the D configuration. The peptide sequence is denoted as D-Arg-2,6-dimethyl-Tyr-Lys-Phe-NH2.' The approved product contains the HYDROCHLORIDE salt — Drugs@FDA lists the active ingredient as ELAMIPRETIDE HYDROCHLORIDE under NDA 215244, and the label gives the chemical name as 'L-Phenylalaninamide, D-arginyl-2,6-dimethyl-L-tyrosyl-L-lysyl-, hydrochloride (1:3)'. THE NAMING IS THE PROBLEM HERE. The same molecule travels under at least four names: elamipretide (INN), SS-31 (the Szeto-Schiller research designation used throughout the literature), MTP-131 and Bendavia (the sponsor's earlier development codes, both of which appear in Stealth's own trial registrations and in FDA's review tables), and FORZINITY (the approved brand). A reader searching 'SS-31' and a regulator searching 'elamipretide' are looking at one substance, and the mismatch is a large part of why material sold as SS-31 is discussed as though no FDA record existed. It does — see below.
FDA status
FDA has approved this as a drug. Approval is always for a specific indication and a specific population — check which one, because it is frequently not the use it is marketed for.
FDA-approved, and the qualifier in front of the word is doing all the work: this is an ACCELERATED approval under section 506(c) and 21 CFR 314.510, for ONE indication, in ONE ultra-rare genetic disease, on an intermediate clinical endpoint. Cross-checked against Drugs@FDA via the openFDA `drug/drugsfda` endpoint on 2026-08-02: NDA 215244, sponsor STEALTH BIOTHERAPS, ORIG-1 submission status AP dated 20250919, review priority PRIORITY, submission class Type 1 New Molecular Entity, orphan property, one product — FORZINITY, solution, subcutaneous, marketing status Prescription. Both `openfda.generic_name` and `products.active_ingredients.name` return the same single application, so this is not an artifact of one query field. This status does NOT travel. It attaches to the approved product, at the approved indication, in the approved population. It says nothing about material sold as SS-31, and nothing about the uses — mitochondrial myopathy, heart failure, macular degeneration, anti-aging — for which no approval exists.
“This NDA provides for the use of Forzinity (elamipretide) injection to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg. … We have completed our review of this application, as amended. It is approved under accelerated approval pursuant to section 506(c) of the Federal Food, Drug, and Cosmetic Act (FDCA) and 21 CFR 314.510, effective on the date of this letter, for use as recommended in the enclosed agreed-upon labeling.”Checked against the source on .
Evidence
There is human data, but efficacy is not established. This includes programmes that were tested and failed.
ADMINISTRATION CHECK RUN, NOT ASSUMED. TAZPOWER (NCT03098797) was opened and read on 2026-08-02: intervention type DRUG, elamipretide given by subcutaneous injection versus placebo, randomized crossover, quadruple-masked, enrolment 12 ACTUAL, lead sponsor Stealth BioTherapeutics Inc., status COMPLETED, results first posted 2024-04-16. Elamipretide was ADMINISTERED to human participants — this is not the endogenous-biomarker trap that reduces MOTS-c and TB-500 from an apparent five human RCTs to an actual zero. SO WHY IS AN FDA-APPROVED DRUG NOT 'proven-in-humans'? Because that tier means efficacy established by adequate, well-controlled human trials, and the documents will not carry it. Read the label's own section 14, quoted above: the randomized, placebo-controlled trial MISSED BOTH PRIMARY ENDPOINTS, and the muscle-strength increases that the approval rests on were NOT seen during that trial — they appeared in the uncontrolled, open-label, single-arm extension in which every participant knew they were receiving drug. FDA's own clinical reviewers, biostatistical reviewers and Cross-Discipline Team Leader concluded there was not substantial evidence of effectiveness and recommended a Complete Response; the signatory authority overruled them on the basis of disease rarity and unmet need, and wrote that the conclusion 'accepts more uncertainty than we would for less rare diseases'. Both of those positions are recorded verbatim, with their own sources, under fdaFindings. The confirmatory randomized trial FDA required (NCT07531251) only began enrolling on 2026-07-02, with estimated primary completion 2029-09-30. This tier is therefore not a criticism of the approval decision — accelerated approval is designed to permit exactly this trade — it is an accurate statement of where the evidence stands. 'Approved' and 'proven' are different claims, and elamipretide is the clearest case on this site where they diverge. Scope: this tier attaches to Barth syndrome, the only indication studied to approval. For primary mitochondrial myopathy the Phase 3 programme was terminated for missing its primary endpoints, and for dry age-related macular degeneration a Phase 3 (NCT06373731) is still running with no result.
“FORZINITY was evaluated in a randomized, double-blind, placebo-controlled, crossover trial and its 192-week, open-label, single-arm extension period. The randomized trial evaluated the efficacy and safety of once daily FORZINITY … in 12 subjects ≥12-years-old and >30 kg with genetically confirmed Barth syndrome. The primary endpoints for the randomized trial were distance walked during 6-minute walk test and Total Fatigue Score on the Barth syndrome Symptom Assessment. FORZINITY was not superior to placebo on these primary endpoints. … Increases in knee extensor muscle strength were not observed during the randomized trial but were observed during the extension period.”Checked against the source on .
What FDA actually approved
- Application
- NDA 215244 — FORZINITY
- Approved indication
- FORZINITY is indicated to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg. This indication is approved under accelerated approval based on an improvement in knee extensor muscle strength, an intermediate clinical endpoint [see Clinical Studies (14)]. Continued approval for this indication may be contingent upon verification and description of clinical benefit in a confirmatory trial.
Verbatim from section 1 of the FDA-approved labeling, second paragraph included because the second paragraph IS the indication — an accelerated approval on an intermediate endpoint is a different object from a full approval, and quoting only the first sentence would misstate what FDA granted. Read the boundaries. The indication is ONE disease (Barth syndrome, an X-linked TAFAZZIN-related mitochondrial disorder FDA's review puts at roughly 150 patients in the United States), ONE outcome ('to improve muscle strength'), and a weight floor (30 kg) that FDA's review states came from the trial's own eligibility criteria rather than from any finding about lighter patients. It is not an approval for mitochondrial function, energy, fatigue, exercise capacity, cardiac function or ageing. FDA's review is explicit that the endpoint behind it 'assessed only a single muscle group' — that finding is recorded with its own source below. `discontinued` is false: Drugs@FDA lists the single FORZINITY product with marketing status Prescription as of the 2026-07-31 data refresh.
What FDA found
FDA’s own words. These are the most citable thing on this site, and the least likely to appear anywhere funded by someone selling the compound.
FDA has recorded that the clinical and biostatistical reviewers and the Cross-Discipline Team Leader on this application concluded there is not substantial evidence of effectiveness on knee muscle strength for accelerated approval, and recommended a Complete Response action. Their conclusion was overruled by the signatory authority.
The single most load-bearing document on this record, and it is FDA disagreeing with itself in public. This is not an outside critic and not a short-seller note — it is the Integrated Review of the approved application, stating that the review team recommended rejection. The review also records the team's conclusion in statutory terms: that SPIBA-201, Part 1 'is an adequate and well-controlled trial that did not demonstrate a treatment effect', that Part 2 'is not an adequate and well-controlled trial', and hence that 'this NDA does not meet the statutory requirement of substantial evidence of effectiveness, even in the context of a rare disease'. What this finding is NOT: it is not evidence that the approval was improper. Accelerated approval exists precisely so that a signatory authority can accept more uncertainty for a serious disease with no treatment, and the reasoning for doing so is recorded here too and quoted in the next finding. Both halves belong on the page. A record that carried only the dissent would be as misleading as the vendor pages that carry only the word 'FDA-approved'.
NDA 215244Orig1s000 — Integrated Review (NDA Re-submission Review), Forzinity (elamipretide) — FDA, 2 October 2025“The clinical and biostatistical reviewers and the Cross-Discipline Team Leader (CDTL) conclude that there is not substantial evidence of effectiveness on knee muscle strength for accelerated approval and recommend a Complete Response action. They note several limitations of the knee muscle strength data, including, but not limited to, the open-label design of SPIBA-201, Part 2, the lack of a control arm, and the potential impact of known and unknown sources of bias (e.g., subject attrition, effort-dependence).”
Checked against the source on .FDA has stated that its conclusion of an effect on knee extensor muscle strength accepts more uncertainty than it would accept for less rare or common diseases, and that the signatory authority concluded this greater uncertainty is acceptable in the context of a disease affecting approximately 150 patients in the United States with no approved treatments.
The other half of the decision, in FDA's words, and the reason this record does not read as an accusation. FDA is not claiming certainty and then hiding the doubt — it wrote the doubt into the approval document. The reasoning is explicitly rarity-scaled: the same evidence in a common disease would not have been accepted. That is precisely why the approval cannot be lifted out of Barth syndrome and used as a general endorsement of the molecule, which is the move the consumer market makes with it.
NDA 215244Orig1s000 — Integrated Review (NDA Re-submission Review), Forzinity (elamipretide) — FDA, 2 October 2025“The signatory authority agrees that there is more uncertainty than we would accept for more common diseases, but concludes that we should accept the extent of uncertainty in the data in the context of this very rare (~150 subjects in the United States), serious disease with no approved treatments … The signatory authority concludes this greater uncertainty is acceptable in this context, when balanced against the risk of rejecting or delaying the marketing of an effective therapy.”
Checked against the source on .FDA has stated that the observed muscle strength measurement involves only a single muscle group and is not accompanied by substantial evidence demonstrating an effect of elamipretide on an appropriate functional measure or on any endpoint directly measuring clinical benefit.
This is the sentence that defines what the approval does and does not assert. An intermediate clinical endpoint is, by definition, not clinical benefit — it is a measure 'reasonably likely to predict' it, and the prediction is the thing the confirmatory trial exists to test. FDA's benefit-risk table says the same thing in the other direction: 'we cannot conclude at the present time that the observed increases in muscle strength in a single muscle group assessed using HHD provides clinical benefit.' Anyone reading 'FDA-approved to improve muscle strength' as 'FDA found it makes patients function better' is reading past a sentence FDA wrote to prevent exactly that.
NDA 215244Orig1s000 — Integrated Review (NDA Re-submission Review), Forzinity (elamipretide) — FDA, 2 October 2025“The observed muscle strength measurement by HHD involves only a single muscle group (knee extensor muscles) and is not accompanied by substantial evidence demonstrating an effect of elamipretide on an appropriate functional measure or on any endpoints directly measuring clinical benefit.”
Checked against the source on .FDA has stated that the randomized, double-blind, placebo-controlled crossover trial did not show superiority of elamipretide to placebo on either component of its primary endpoint family — distance walked on the 6-minute walk test (p=0.97) and total fatigue score on the Barth syndrome symptom assessment (p=0.89) — and that none of the secondary endpoints achieved even nominal statistical significance (p=0.21-1.00).
The controlled evidence, stated by FDA with the p-values attached. p=0.97 and p=0.89 are not near-misses; they are the numbers you get when nothing separated. FDA's benefit-risk table restates it flatly: 'Elamipretide was not superior to placebo on any of these endpoints' in Part 1, across the 6-minute walk test, fatigue, knee extensor strength, 5-times sit-to-stand, Sway balance, echocardiographic parameters and MLCL:CL ratios. The label carries the same finding in plainer words — 'FORZINITY was not superior to placebo on these primary endpoints' — which is why it is quoted against the label under `evidence` and against the review here. Two documents, one finding, no reliance on either alone.
NDA 215244Orig1s000 — Integrated Review (NDA Re-submission Review), Forzinity (elamipretide) — FDA, 2 October 2025“SPIBA-201, Part 1 did not show superiority of elamipretide to placebo at the end of 12 weeks of treatment on the primary endpoint family of distance walked on 6-minute walk test (6MWT) (p=0.97) and total fatigue score (TFS) on the Barth syndrome symptom assessment (BTHA-SA) (p=0.89). While no alpha remained to test secondary endpoints, it is notable that none of the secondary endpoints achieved even nominal statistical significance (p=0.21-1.00).”
Checked against the source on .FDA has stated that elamipretide does not directly target the underlying genetic defect that causes Barth syndrome, nor does it meaningfully impact the elevated cardiolipin ratio, the direct sequelae of the mutation in the Tafazzin gene.
Recorded because the mechanism story is what the consumer market actually sells. Elamipretide is marketed as a cardiolipin-targeting mitochondrial repair peptide, and the FDA-approved label does describe it as 'a mitochondrial cardiolipin binder that localizes to the inner mitochondrial membrane'. But in the one human disease where the cardiolipin defect is the whole pathology, FDA's reviewers recorded that the drug did not meaningfully move the cardiolipin ratio. A binding mechanism that is real at the membrane is not the same as a measured effect on the biochemistry, and neither is the same as clinical benefit. Attribution note: this sentence states the review team's position, and the signatory authority took a different view of the same nonclinical data, concluding that reliance on it as confirmatory evidence 'in this very rare disease and narrowly defined context is reasonable'.
NDA 215244Orig1s000 — Integrated Review (NDA Re-submission Review), Forzinity (elamipretide) — FDA, 2 October 2025“They also note that while there is some nonclinical mechanistic data, elamipretide does not directly target the underlying genetic defect that causes BTHS, nor does it meaningfully impact the elevated cardiolipin ratio, the direct sequelae of the mutation in the Tafazzin gene.”
Checked against the source on .FDA required a randomized, double-blind, placebo-controlled confirmatory trial in patients 5 years and older with Barth syndrome to verify and describe the clinical benefit predicted by improvements in knee extensor muscle strength, and stated that if the required postmarketing clinical trial fails to verify clinical benefit or is not conducted with due diligence, it may withdraw this approval.
The approval is conditional and FDA says so in the approval letter itself. The agreed timetable in the letter runs: study initiation 03/2026, full enrolment 03/2028, study completion 09/2029, final report 03/2030. That is the earliest date on which anyone will know whether the muscle-strength finding predicts clinical benefit. Three further postmarketing requirements sit alongside it under section 505(o), and they are worth naming because they describe what is NOT yet known about long-term exposure: 4802-2, a 26-week carcinogenicity study in TgRasH2 mice; 4802-3, a 2-year carcinogenicity study in rats, final report due 01/2030; and 4802-4, a clinical pharmacokinetic study of the effect of Forzinity on metformin, a sensitive MATE1 substrate. FDA imposed the carcinogenicity studies having determined that spontaneous adverse-event reporting 'will not be sufficient to identify an unexpected serious risk of carcinogenicity and drug-drug interactions'. Carcinogenicity is an open question with a 2030 answer date.
NDA 215244 — ACCELERATED APPROVAL letter, Forzinity (elamipretide) injection — FDA, 19 September 2025“Pursuant to section 506(c) of the FDCA and 21 CFR 314.510 you are required to conduct an adequate and well-controlled clinical trial intended to verify and describe clinical benefit. You are required to conduct this clinical trial with due diligence. If your required postmarketing clinical trial fails to verify clinical benefit or is not conducted with due diligence, including with respect to the conditions set forth below, we may withdraw this approval. … 4802-1 Conduct a randomized, double-blind, placebo-controlled trial in patients 5 years and older with Barth syndrome to verify and describe the clinical benefit of Forzinity predicted by improvements in knee extensor muscle strength assessed by handheld dynamometry”
Checked against the source on .FDA granted accelerated approval even though the required post-approval confirmatory trial was not underway at the time of approval, stating it had sufficient assurances from the applicant that the trial would be conducted diligently and in a timely manner.
Recorded because the timeline is the part everyone skips. The approval issued 2025-09-19 with no confirmatory trial running. The confirmatory trial — SPIBA-401, registered as NCT07531251, a Phase 3b/4 randomized, double-blind, placebo-controlled, parallel-group trial in genetically confirmed Barth syndrome — posted its first registration 2026-04-15 and records an actual start date of 2026-07-02, with estimated primary completion 2029-09-30. As of 2026-08-02 it is RECRUITING with an estimated enrolment of 48. Its own registered summary states the objective in the sponsor's words: 'The primary trial objective is to confirm the efficacy of elamipretide which is approved in the United States (FORZINITY™) under the accelerated approval based on an improvement in knee extensor muscle strength, an intermediate clinical endpoint.' The confirmation is pending, by the sponsor's own description.
NDA 215244Orig1s000 — Integrated Review (NDA Re-submission Review), Forzinity (elamipretide) — FDA, 2 October 2025“we have sufficient assurances from the Applicant that they will conduct the trial in a diligent and timely manner and have concluded that granting accelerated approval of elamipretide is appropriate at this time even though the post-approval confirmatory trial is not underway.”
Checked against the source on .FDA issued a Complete Response letter on this application on 15 May 2025, before the resubmission that led to approval.
The regulatory history in one line, from the approval letter. FDA's Integrated Review adds what the Complete Response was about: FDA declined to approve on the endpoints originally proposed, the Signatory Authority identified knee extensor muscle strength as a possible intermediate clinical endpoint, and the letter also 'noted deficiencies at the drug product manufacturing facility that would need to be resolved before this application could be approved'. On resubmission the Office of Pharmaceutical Quality confirmed the facility deficiencies were resolved. SOURCING CAUTION: the Integrated Review's narrative sentence about this letter contains an evident typographical error in the year. The date used here is taken from the approval letter, which is unambiguous.
NDA 215244 — ACCELERATED APPROVAL letter, Forzinity (elamipretide) injection — FDA, 19 September 2025“Please refer to your new drug application (NDA) dated January 29, 2024, received January 29, 2024, and your amendments, submitted under section 505(b) of the Federal Food, Drug, and Cosmetic Act (FDCA) for Forzinity (elamipretide) injection. We acknowledge receipt of your amendment dated August 15, 2025, which constituted a complete response to our May 15, 2025, action letter.”
Checked against the source on .Elamipretide appears in none of Categories 1, 2 or 3 of the 503A bulk drug substances list updated 2026-05-14.
Recorded to close a misreading, not to assert a status — which is why this record carries no compoundingStatus at all. Verified by fetching the document with a browser user-agent and text-extracting it locally on 2026-08-02: zero hits for 'elamipretide', and zero for 'SS-31', 'MTP-131' and 'Bendavia'. This absence means something different from BPC-157's absence. BPC-157 was nominated and left Category 2 when its nominators withdrew. Elamipretide was never in the 503A nomination system at all — that route is for substances WITHOUT an approved product, and elamipretide has one. Categorical silence here is neither permission nor a safety finding, and it is emphatically not a route by which material sold as SS-31 becomes compoundable.
Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the Federal Food, Drug, and Cosmetic Act — FDA, 14 May 2026Checked against the source on .
Documented safety signals
The FDA-approved labeling warns of the risk of benzyl alcohol toxicity in neonates. FORZINITY contains benzyl alcohol as a preservative and is not approved for use in neonates. Serious adverse reactions, including fatal reactions, of new onset or worsening metabolic acidosis that progressed to neurotoxicity, and in some cases gasping syndrome, have been reported in low-birth weight and preterm neonates who received benzyl alcohol-containing drugs intravenously.
The only Warnings and Precautions entry in the Highlights, and it is about an EXCIPIENT rather than the peptide. Worth reading precisely for that reason: what is in the vial alongside the active ingredient carries its own labeled risk, and FDA states the minimum quantity at which these reactions occur is not known. There is no boxed warning on this label.
FORZINITY (elamipretide) injection, for subcutaneous use — Prescribing Information — FDA, 19 September 2025“FORZINITY is not approved for use in neonates. Serious adverse reactions, including fatal reactions, of new onset or worsening metabolic acidosis that progressed to neurotoxicity, and in some cases gasping syndrome, have been reported in low-birth weight neonates (less than 2,500 grams) and preterm neonates (gestational age less than 34 weeks) who received benzyl alcohol (BA)-containing drugs intravenously. … The minimum amount of BA at which these serious adverse reactions, including fatal reactions, may occur is not known.”
Checked against the source on .The FDA-approved labeling warns of hypersensitivity reactions, including serious allergic reactions requiring emergency medical intervention, reported in patients receiving FORZINITY. Serious hypersensitivity to elamipretide or any excipient is a contraindication.
Note the window FDA specifies: 'within minutes to months after treatment initiation'. A tolerated first injection is not evidence of a tolerated course. The label directs that if a serious hypersensitivity reaction occurs the drug is stopped and emergency treatment instituted 'including epinephrine, antihistamines, and corticosteroids as clinically indicated', and that such patients 'should not be rechallenged'. This is a monitoring instruction to a prescriber, and it is the kind of instruction that does not exist at all for an unapproved vial bought under a research label.
FORZINITY (elamipretide) injection, for subcutaneous use — Prescribing Information — FDA, 19 September 2025“Hypersensitivity reactions, including serious allergic reactions requiring emergency medical intervention, have been reported in patients receiving FORZINITY. These reactions have included skin manifestations such as rash, papular lesions, and eczematous dermatitis, as well as respiratory symptoms including cough … Reactions may occur within minutes to months after treatment initiation.”
Checked against the source on .In the placebo-controlled crossover trial, local administration reactions were reported in 12 of 12 subjects (100%) during elamipretide treatment versus 8 of 12 (67%) during placebo. Injection site erythema was reported in 12 of 12 (100%) on elamipretide versus 3 of 12 (25%) on placebo. FDA's review records that injection site reactions were the most common adverse reactions and occurred in all 12 elamipretide-treated subjects.
The counts above are read directly from Table 2 of the label (Barth Safety Population, Periods 1 and 2 combined, N=12 per arm) and are corroborated in FDA's Integrated Review, which states: 'The most common adverse reactions were injection site reactions, which occurred in all 12 elamipretide treated subjects.' A 100% incidence is unusual enough to state plainly rather than round into 'the most common adverse reaction'. FDA's benefit-risk assessment characterises this as a tolerability issue rather than a life-threatening one.
FORZINITY (elamipretide) injection, for subcutaneous use — Prescribing Information — FDA, 19 September 2025“Adverse reactions occurring more commonly on FORZINITY than on placebo include injection site reactions such as injection site erythema, pain, induration, pruritus, bruising, and urticaria (Table 2).”
Checked against the source on .The FDA-approved labeling records that increases in absolute eosinophil counts were noted frequently in studies where the duration of administration was 30 days or greater, peaking around 90 days after initial exposure and returning to baseline after 6 to 12 months of continued treatment.
Quoted with a trailing ellipsis where the label gives a numeric magnitude, and truncated at a page break in the source PDF. FDA's Integrated Review adds the trial-level figure: 'Mild eosinophilia (>0.65×103 cells/uL) was observed in 9 of 12 elamipretide-treated subjects', and characterises the increases as apparently transient and not associated with clinical manifestations of eosinophilia. Recorded because it is a laboratory signal that only appears with continued exposure — nobody self-administering an unapproved vial is having eosinophil counts checked.
FORZINITY (elamipretide) injection, for subcutaneous use — Prescribing Information — FDA, 19 September 2025“Increases in absolute eosinophil counts were noted frequently in studies where duration of administration of FORZINITY was 30 days or greater. Eosinophil counts generally peaked around 90 days after initial exposure … and returned to baseline levels after 6 to 12 months of”
Checked against the source on .FDA has stated that the safety database in subjects with Barth syndrome is limited: safety was assessed in 12 subjects, the placebo-controlled safety data are limited to 12 weeks of exposure, and total cumulative exposure in the open-label extension was 26 subject-years across 10 subjects.
The number that puts every safety claim about this molecule in proportion. Twelve people with Barth syndrome received elamipretide in the programme that supported approval, and the controlled safety comparison covers a single 12-week period. FDA judged that database 'limited but acceptable given the rarity of the disease' — a judgement scaled to a 150-patient disease with no alternative. It is not a general safety clearance, and it cannot support any claim about the safety of long-term use in healthy adults, for whom the approved product was never studied and for whom two carcinogenicity studies remain outstanding as postmarketing requirements.
NDA 215244Orig1s000 — Integrated Review (NDA Re-submission Review), Forzinity (elamipretide) — FDA, 2 October 2025“Safety was assessed in 12 subjects with BTHS who received elamipretide including four adult and eight pediatric subjects. The placebo-controlled safety data are limited to 12 weeks of elamipretide exposure. … Total cumulative exposure was 26 subject-years; 7 subjects had greater than 144 weeks of exposure. … The safety database in subjects with BTHS is limited but acceptable given the rarity of the disease.”
Checked against the source on .
Questions people actually ask
Every answer cites the document behind it. Where the honest answer is “nobody knows”, that is the answer you will get.
- Is SS-31 the same thing as elamipretide?
Yes. SS-31 is the Szeto-Schiller research designation for the peptide whose international nonproprietary name is elamipretide, and the two names are used interchangeably in the peer-reviewed literature — a 2023 paper in Antioxidants is titled 'Elamipretide(SS-31) Attenuates Idiopathic Pulmonary Fibrosis by Inhibiting the Nrf2-Dependent NLRP3 Inflammasome in Macrophages'. The same molecule also carried the development codes MTP-131 and Bendavia, both of which appear in its sponsor's own trial registrations, and it is sold as an FDA-approved drug under the brand name FORZINITY. The naming matters more than it sounds: someone searching 'SS-31' and a regulator searching 'elamipretide' are looking at one substance, and material sold as SS-31 is routinely discussed as though there were no FDA record of it. There is — an approved NDA, a published label, an approval letter and a full review.
Elamipretide(SS-31) Attenuates Idiopathic Pulmonary Fibrosis by Inhibiting the Nrf2-Dependent NLRP3 Inflammasome in Macrophages (Nie Y, Li J, Zhai X, Wang Z) — PubMed, 21 November 2023Checked against the source on .- Is elamipretide FDA-approved in 2026?
Yes, narrowly. FDA granted accelerated approval to FORZINITY (elamipretide) injection under NDA 215244 on 19 September 2025, to Stealth BioTherapeutics. The approval letter states that it 'is approved under accelerated approval pursuant to section 506(c) of the Federal Food, Drug, and Cosmetic Act (FDCA) and 21 CFR 314.510'. That is the whole of the approval: one application, one product, one indication — improving muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg. Barth syndrome is an X-linked mitochondrial disease that FDA's review puts at roughly 150 patients in the United States. Accelerated approval is a conditional pathway: FDA required a confirmatory randomized, placebo-controlled trial and stated in the same letter that if that trial 'fails to verify clinical benefit or is not conducted with due diligence … we may withdraw this approval.'
NDA 215244 — ACCELERATED APPROVAL letter, Forzinity (elamipretide) injection — FDA, 19 September 2025“It is approved under accelerated approval pursuant to section 506(c) of the Federal Food, Drug, and Cosmetic Act (FDCA) and 21 CFR 314.510, effective on the date of this letter, for use as recommended in the enclosed agreed-upon labeling.”
Checked against the source on .- Did the elamipretide trial in Barth syndrome actually work?
Not on its primary endpoints. The FDA-approved labeling for FORZINITY states, in section 14, that the randomized, double-blind, placebo-controlled crossover trial had primary endpoints of distance walked during the 6-minute walk test and total fatigue score on the Barth syndrome Symptom Assessment, and that 'FORZINITY was not superior to placebo on these primary endpoints.' FDA's Integrated Review gives the numbers: p=0.97 and p=0.89 respectively, and adds that 'none of the secondary endpoints achieved even nominal statistical significance (p=0.21-1.00).' The finding the approval rests on — increased knee extensor muscle strength measured by handheld dynamometry — came from somewhere else. The label is explicit: 'Increases in knee extensor muscle strength were not observed during the randomized trial but were observed during the extension period', an open-label, single-arm extension in which every participant knew they were receiving drug. That is why FDA treated muscle strength as an intermediate clinical endpoint reasonably likely to predict benefit, rather than as demonstrated benefit.
FORZINITY (elamipretide) injection, for subcutaneous use — Prescribing Information — FDA, 19 September 2025“FORZINITY was not superior to placebo on these primary endpoints. … Increases in knee extensor muscle strength were not observed during the randomized trial but were observed during the extension period.”
Checked against the source on .- Did FDA's own reviewers agree that elamipretide should be approved?
No. FDA's Integrated Review of the resubmitted application records that 'the clinical and biostatistical reviewers and the Cross-Discipline Team Leader (CDTL) conclude that there is not substantial evidence of effectiveness on knee muscle strength for accelerated approval and recommend a Complete Response action.' They cited the open-label design of the extension study, the lack of a control arm, and known and unknown sources of bias including subject attrition and effort-dependence. The signatory authority approved the application over that recommendation, writing that there is 'more uncertainty than we would accept for more common diseases' but that the uncertainty should be accepted 'in the context of this very rare (~150 subjects in the United States), serious disease with no approved treatments.' Both positions are in the same FDA document. Neither one is the whole story, and a page that quotes only 'FDA-approved' is quoting the shortest part of it.
NDA 215244Orig1s000 — Integrated Review (NDA Re-submission Review), Forzinity (elamipretide) — FDA, 2 October 2025“The clinical and biostatistical reviewers and the Cross-Discipline Team Leader (CDTL) conclude that there is not substantial evidence of effectiveness on knee muscle strength for accelerated approval and recommend a Complete Response action.”
Checked against the source on .- Is elamipretide or SS-31 approved for anti-aging, energy or mitochondrial health?
No. The FDA-approved labeling for FORZINITY contains exactly one indication: 'FORZINITY is indicated to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg.' There is no approved indication for ageing, fatigue, energy, exercise capacity, cognitive function, cardiac function or general mitochondrial support, and the label's second paragraph limits even the approved claim, stating the indication is granted 'under accelerated approval based on an improvement in knee extensor muscle strength, an intermediate clinical endpoint' whose continued approval 'may be contingent upon verification and description of clinical benefit in a confirmatory trial.' FDA's review is blunter still about the reach of that endpoint: it 'involves only a single muscle group (knee extensor muscles) and is not accompanied by substantial evidence demonstrating an effect of elamipretide on an appropriate functional measure or on any endpoints directly measuring clinical benefit.' A Phase 2a open-label pilot in older adults did begin at the University of Washington in November 2025 (NCT07275424), which is what an unanswered question looks like, not an answer.
FORZINITY (elamipretide) injection, for subcutaneous use — Prescribing Information — FDA, 19 September 2025“FORZINITY is indicated to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kg. This indication is approved under accelerated approval based on an improvement in knee extensor muscle strength, an intermediate clinical endpoint [see Clinical Studies (14)].”
Checked against the source on .- What happened to the elamipretide Phase 3 trial in mitochondrial myopathy?
It was terminated for missing its primary endpoints. MMPOWER-3 (NCT03323749) was a Phase 3 randomized, placebo-controlled trial of subcutaneous elamipretide in subjects with primary mitochondrial myopathy, sponsored by Stealth BioTherapeutics, with an actual enrolment of 218. Its registry record carries status TERMINATED with the sponsor's own stated reason: 'Part1,double blind portion of the trial did not meet the primary end points.' Primary completion is recorded as 2020-02-10, and results were first posted 2021-04-02. This matters for how the compound is described elsewhere: the genuine Phase 3 programme for elamipretide was in mitochondrial myopathy and it failed, while the Barth syndrome trial behind the FDA approval was a 12-subject crossover trial whose own official title calls it Phase 2. A separate Phase 3 in dry age-related macular degeneration (ReNEW, NCT06373731) was listed as active and not recruiting as of May 2026, with estimated primary completion in August 2027 and no result yet.
MMPOWER-3 — A Phase 3 Randomized, Placebo-Controlled Trial to Evaluate the Efficacy and Safety of Daily Subcutaneous Injections of Elamipretide in Subjects With Primary Mitochondrial Myopathy Followed by an Open-Label Treatment Extension — ClinicalTrials.gov, 24 January 2022“Part1,double blind portion of the trial did not meet the primary end points.”
Checked against the source on .- Can the FDA approval of elamipretide be withdrawn?
Yes — that is a written condition of this particular approval. The FDA approval letter for NDA 215244 states: 'If your required postmarketing clinical trial fails to verify clinical benefit or is not conducted with due diligence, including with respect to the conditions set forth below, we may withdraw this approval.' The required trial is postmarketing requirement 4802-1, 'a randomized, double-blind, placebo-controlled trial in patients 5 years and older with Barth syndrome to verify and describe the clinical benefit of Forzinity predicted by improvements in knee extensor muscle strength assessed by handheld dynamometry.' The agreed timetable in the letter runs to study completion in September 2029 and a final report in March 2030. FDA also noted in its review that it granted the approval 'even though the post-approval confirmatory trial is not underway' at the time; that trial, registered as NCT07531251, records an actual start date of 2 July 2026. Until it reports, the clinical benefit remains, in FDA's framing, predicted rather than verified.
NDA 215244 — ACCELERATED APPROVAL letter, Forzinity (elamipretide) injection — FDA, 19 September 2025“If your required postmarketing clinical trial fails to verify clinical benefit or is not conducted with due diligence, including with respect to the conditions set forth below, we may withdraw this approval.”
Checked against the source on .- Is elamipretide on FDA's 503A list of bulk drug substances for compounding?
No. Elamipretide appears in none of Categories 1, 2 or 3 of FDA's list of bulk drug substances nominated for use in compounding under section 503A, in the version updated 14 May 2026 — and neither do the names SS-31, MTP-131 or Bendavia. Read what that absence does and does not mean. It is not permission and it is not a safety finding. The 503A nomination route exists for substances that have no FDA-approved product; elamipretide has one, so it was never part of that process, which is a different situation from a peptide such as BPC-157 that was nominated and then left Category 2 when its nominators withdrew. For the same reason this record deliberately records no 503A status at all rather than labelling elamipretide 'never-nominated', which would imply a proceeding it was never in.
Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the Federal Food, Drug, and Cosmetic Act — FDA, 14 May 2026Checked against the source on .