MOTS-C vs SS-31
MOTS-c is a 16-amino-acid microprotein encoded within the mitochondrial 12S rRNA gene, described as a retrograde signalling molecule acting on AMPK, one-carbon metabolism and nuclear stress-response gene expression. SS-31, also called elamipretide or MTP-131, is a synthetic mitochondria-targeted tetrapeptide that binds cardiolipin in the inner mitochondrial membrane and stabilises cristae architecture. Both are described as mitochondrial peptides, which is why they are grouped together, but they differ in almost every other respect, including regulatory status: elamipretide received FDA accelerated approval for Barth syndrome in September 2025, while no controlled clinical trial has administered MOTS-c to humans at all. No study has compared the two directly. Their evidence bases are separated by a wide gap in study design and are not interchangeable.
No study has compared them directly.
Everything below is drawn from separate studies that used different models, endpoints and species. That is a real limit on what can be concluded, not a formality.
No published study has administered MOTS-c and elamipretide to the same subjects or compared them in parallel arms in any model. Searches of PubMed and Europe PMC returned only narrative reviews of mitochondrial-targeted interventions and of peptides used in sports medicine, in which both compounds appear in separate sections of the same article. Reviews that list two compounds do not compare them experimentally. Any comparison between them is therefore indirect and drawn from literatures that differ fundamentally in kind: elamipretide has been tested in randomised, double-blind, placebo-controlled human trials with clinical and functional endpoints, whereas interventional MOTS-c data come almost entirely from rodents and cell culture, with human MOTS-c research consisting of observational biomarker measurement and genetic association rather than administration.
Side by side.
| MOTS-C | SS-31 | |
|---|---|---|
| Evidence maturity | Preclinical only | Approved drug |
| Studies cited here | 15 | 16 |
| Published 2023 or later | 12 | 11 |
| Newest paper | 2026 | 2026 |
| Origin and class | Endogenous 16-amino-acid microprotein encoded within the mitochondrial 12S rRNA gene, classed as a mitochondrial-derived peptide or mitokine. | Synthetic mitochondria-targeted tetrapeptide with no endogenous counterpart, developed as a pharmaceutical candidate. |
| Proposed mechanism | Retrograde mitochondrial-to-nuclear signalling, with reported AMPK activation, effects on folate-methionine one-carbon metabolism, Nrf2 and oxidative stress signalling, and direct binding and activation of CK2. | Binding to cardiolipin in the inner mitochondrial membrane, stabilising cristae architecture and improving electron transport efficiency and ATP synthesis. |
| Evidence maturity | Preclinical only with respect to administration. No controlled clinical trial has given exogenous MOTS-c to humans. | Approved drug. FDA accelerated approval was granted on 19 September 2025 for improving muscle strength in adult and paediatric Barth syndrome patients weighing at least 30 kg, with continued approval contingent on confirmatory trials. |
| Nature of the human data | Observational and genetic. Circulating MOTS-c has been measured as a candidate biomarker in metabolic, cardiovascular, renal and reproductive conditions, and the m.1382A>C (K14Q) variant was associated with type 2 diabetes risk in a meta-analysis of three East Asian cohorts totalling 27,527 participants. | Interventional. Randomised, double-blind, placebo-controlled trials in Barth syndrome, primary mitochondrial myopathy, heart failure with reduced ejection fraction and Leber hereditary optic neuropathy, plus a single-dose study in 39 healthy older adults. |
| Record in large controlled trials | None exist to report. | Mixed. The phase 3 MMPOWER-3 trial in 218 participants with primary mitochondrial myopathy missed its primary endpoints, as did the phase 2 PROGRESS-HF heart failure trial in 71 patients and the phase 2 Leber hereditary optic neuropathy trial. The Barth syndrome programme in a 12-patient cohort reported sustained functional gains through a 168-week open-label extension. |
| Strongest interventional finding | In rodents, administered MOTS-c improved insulin sensitivity and glucose tolerance in high-fat-diet and aged mice, and improved physical capacity and muscle homeostasis in young, middle-aged and old mice. | In a randomised, double-blind, placebo-controlled single-dose study, in vivo mitochondrial ATP production measured by phosphorus magnetic resonance spectroscopy improved in the skeletal muscle of 39 healthy older adults. |
| Evidence in healthy people or athletes | Absent for administration. Human exercise work has measured endogenous MOTS-c levels in response to training, heat stress or an acute exercise bout rather than giving the peptide. | Absent apart from the single-dose ATP production study in healthy older adults. There are no controlled trials of elamipretide in healthy individuals for exercise capacity, athletic performance, longevity or body composition. |
And what it does not.
These two compounds share a subcellular target and almost nothing else in terms of what has been demonstrated. Elamipretide has been through the full randomised controlled trial apparatus, and the honest summary of that programme is uneven: an accelerated approval in Barth syndrome resting on a muscle-strength surrogate in a very small cohort, with confirmatory clinical benefit not yet demonstrated, alongside missed primary endpoints in its largest mitochondrial myopathy trial and in its heart failure and optic neuropathy trials. MOTS-c has not reached that stage at all; its interventional results are rodent and cell-culture findings, and its human presence in the literature is as a measured biomarker whose direction of change is not consistent across conditions. The gap between them is a gap in study design, not a demonstration that one compound works and the other does not. Neither has controlled evidence supporting use in healthy people for performance, body composition or ageing, and for MOTS-c even basic human pharmacokinetics, dosing and safety are unestablished.
Common questions.
- Is either compound an approved medicine?
Elamipretide is. The FDA granted accelerated approval on 19 September 2025 for improving muscle strength in adult and paediatric patients with Barth syndrome weighing at least 30 kg, based on an improvement in knee extensor muscle strength, with continued approval contingent on confirmatory trials. MOTS-c holds no approval anywhere, and no controlled clinical trial has administered it to humans.
- What do human MOTS-c studies actually measure?
They measure the peptide that circulates naturally rather than a peptide that was given. Published human work includes cross-sectional comparisons in obesity, polycystic ovary syndrome, acute coronary syndrome and cerebral palsy, a mitochondrial genotype association in 27,527 East Asian participants, and exercise or heat-stress studies tracking endogenous levels. None of these designs can establish what administering MOTS-c would do.
- Did the largest elamipretide trial succeed?
No. MMPOWER-3, a phase 3 randomised, double-blind, placebo-controlled trial in 218 participants with primary mitochondrial myopathy over 24 weeks, missed its primary endpoints. A post hoc genotype-stratified analysis was published later. The phase 2 PROGRESS-HF trial in heart failure with reduced ejection fraction and the phase 2 topical ophthalmic trial in Leber hereditary optic neuropathy also did not meet their primary endpoints.
- Why is circulating MOTS-c described as an unsettled biomarker?
Because its direction of change is not consistent across conditions. Published reports describe lower levels in diabetes and in women with polycystic ovary syndrome, but higher levels in adults with obesity and in acute coronary syndrome. Assay standardisation also differs between studies. That combination makes it difficult to interpret a single measurement as indicating mitochondrial health in one direction or the other.
- Does the rodent MOTS-c work translate to the outcomes people care about?
That has not been tested. Administered MOTS-c improved insulin sensitivity and glucose tolerance in high-fat-diet and aged mice, improved physical capacity in young, middle-aged and old mice, and improved skeletal muscle mitochondrial bioenergetics in transgenic strains. Translation to humans requires a controlled trial that has not been conducted, so dosing, pharmacokinetics, long-term safety and functional benefit in people remain unestablished.
For research purposes only. Not for human consumption, diagnosis, treatment, or prevention of any condition. Nothing on this page is medical advice, and no comparison here should be read as a recommendation of either compound.