MOTS-c

What it is

Mitochondria carry their own small genome, a relic of the bacterium they descend from. For most of modern biology that genome was assumed to encode only respiratory-chain subunits and the RNA machinery to make them. Then researchers found short open reading frames hidden inside it that encode small signalling peptides — first humanin, then, in 2015, a sixteen-residue peptide read out of the 12S rRNA gene and named MOTS-c: mitochondrial open reading frame of the 12S rRNA type-c.

That is a real and significant discovery. It means mitochondria are not merely power plants taking instructions from the nucleus — they send signals back, in their own genetic language. Whether that discovery justifies injecting the peptide is an entirely separate question.

What it does in the body

In the discovery work, MOTS-c’s primary target organ appeared to be skeletal muscle. Its cellular action was specific and somewhat counterintuitive: it inhibits the folate cycle and the de novo purine biosynthesis tethered to it, which causes an accumulation of the metabolite AICAR, which in turn activates AMPK — the master energy sensor that switches cells from storing fuel to burning it. In mice, MOTS-c treatment prevented both age-dependent and high-fat-diet-induced insulin resistance, and prevented diet-induced obesity.

A follow-up paper reported that MOTS-c enhanced physical performance in young, middle-aged and old mice, regulated nuclear genes related to metabolism and proteostasis, and that intermittent treatment started very late in life increased physical capacity and healthspan. The same paper reported the human-relevant finding: exercise induces endogenous MOTS-c expression in human skeletal muscle and in circulation.

That last point is worth isolating, because it is the most reliably established human fact about MOTS-c and it is often inverted in marketing. Exercise raises MOTS-c. That is not evidence that raising MOTS-c substitutes for exercise.

What the human evidence shows

No published trial has administered MOTS-c to humans. What exists in people is observational and correlational:

• Exercise induces MOTS-c expression in human muscle and plasma.
• Randomised exercise interventions have measured circulating MOTS-c as an outcome — for example in breast-cancer survivors undergoing aerobic and resistance training, and in a 2025 trial of repeated heat stress during calf-muscle immobilisation, where MOTS-c and FGF21 were tracked as “mitokines”.
• Serum MOTS-c has been examined as a biomarker in conditions including polycystic ovary syndrome and multiple myeloma, with lower levels reported alongside mitochondrial dysfunction in some studies.

All of that is MOTS-c as a measurement. None of it is MOTS-c as a treatment.

The nearest thing to a human therapeutic test used an analogue, not MOTS-c itself. A company developed CB4211, described as a MOTS-c analogue, and reported topline phase 1a/1b results in 2021: roughly 20 obese participants with non-alcoholic fatty liver disease received 25 mg daily subcutaneously or placebo for four weeks. The company reported the drug was well tolerated with no serious adverse events, the commonest events being transient mild-to-moderate injection-site reactions. ALT fell 21% from baseline versus a 4% rise on placebo, AST fell 28% versus 11%, and glucose fell 6% versus no change, each reported as statistically significant. Body weight showed only a trend. Liver fat fell substantially in both arms, so the trial showed no drug-specific effect on the outcome it was most interested in. These are company-reported topline figures in about twenty people over four weeks, not a peer-reviewed publication, and they concern a different molecule.

Claims and what backs them

Risks and unknowns

No human safety data for the peptide itself. Not a single published trial. Everything about dose, exposure, immunogenicity and long-term effect is unknown.

AMPK activation is not uniformly benign. AMPK sits at the centre of cellular energy decisions and interacts with growth and proliferation signalling. Chronic pharmacological activation of a master metabolic regulator in a healthy person has consequences that have not been mapped. Notably, WADA classifies AMPK activators alongside PPARδ agonists as metabolic modulators precisely because they alter fuel use systemically.

The identity problem the FDA raised applies here too. When agency staff reviewed these peptides, their lead objection was that for several of them there was no universally accepted chemical definition and, for some, simply no data to assess.

A sport-specific trap. MOTS-c sits in a WADA class whose substances are non-Specified, which carries less scope for reduced sanctions than the Specified classes. An athlete who assumes an obscure research peptide is not on the list would be wrong, and expensively so.

Where regulators stand

The bottom line

MOTS-c is the best biology and the thinnest human evidence in this atlas. A peptide encoded in mitochondrial DNA that signals to the nucleus and is released by exercise is a genuinely important finding, and the mouse metabolic data are striking.

What follows from that for a person in 2026 is: nothing yet. No one has given MOTS-c to humans in a published trial. The closest attempt used an analogue in about twenty people for a month and showed liver fat improving equally on placebo. And the one group with a clear rule on it — anti-doping authorities — named it explicitly and banned it at all times.

References

1. Lee C, Zeng J, Drew BG, et al. The mitochondrial-derived peptide MOTS-c promotes metabolic homeostasis and reduces obesity and insulin resistance. Cell Metab. 2015;21(3):443–454 PMID 25738459
2. Reynolds JC, Lai RW, Woodhead JST, et al. MOTS-c is an exercise-induced mitochondrial-encoded regulator of age-dependent physical decline and muscle homeostasis. Nat Commun. 2021;12(1):470 PMID 33473109
3. Dieli-Conwright CM, Sami N, Norris MK, et al. Effect of aerobic and resistance exercise on the mitochondrial peptide MOTS-c in Hispanic and non-Hispanic white breast cancer survivors. Sci Rep. 2021;11:16916 PMID 34413391
4. Elhusseiny R, Ihsan M, Labidi M, et al. Repeated heat stress modulates the levels of the mitokines MOTS-c and FGF21 in active men during calf muscle immobilization. Med Sci Sports Exerc. 2025;57(12):2764–2774 PMID 40674654
5. World Anti-Doping Agency. The 2026 Prohibited List, International Standard. In force 1 January 2026 — class S4.4.1 Source
6. US Food and Drug Administration. Certain bulk drug substances for use in compounding that may present significant safety risks. Content current as of 22 April 2026 Source