Performance & GH axis
Irisin
FNDC5 fragment
Irisin is a peptide cleaved from the membrane protein FNDC5 and released from muscle during exercise. It was proposed in 2012 as the mediator that converts white fat to brown, and its existence and importance have been contested ever since.
Also known as: FNDC5, irisin myokine
- Status
- Irisin is a research compound and not approved by the FDA for human use.
- Evidence
- Preclinical. Evidence comes from animal or lab studies; effects in people are not established.
- Half-life
- Short; not well characterised in humans.
- How it's taken
- Not available as a therapeutic; research use only
- Mechanism
- Metabolic (non-incretin)
- Pathways
- Mitochondrial
How Irisin works
Exercise increases PGC-1alpha, which raises FNDC5 expression; proteolytic cleavage releases irisin into the circulation. The original proposal was that irisin acts on white adipose tissue to induce UCP1 expression and a brown-fat-like thermogenic phenotype, and separately on bone and brain. The receptor was later identified as an integrin complex.
What research has looked at
- The underlying idea — that muscle secretes signalling molecules coupling exercise to distant tissue adaptation — is well established, and irisin was a landmark example of the myokine concept.
- Mass spectrometry work confirmed that irisin does circulate in humans and rises modestly with exercise, resolving part of the early controversy.
- Animal studies support effects on bone density and on hippocampal function.
Evidence level: Preclinical. Evidence comes from animal or lab studies; effects in people are not established. These are areas studied or reported, not promised effects.
Reported side effects and risks
- A substantial part of the early literature used commercial ELISA kits later shown to be non-specific, meaning many published irisin measurements were unreliable. This is one of the clearest recent cases of an assay artefact driving a field. No regulator has approved it, the human evidence base is limited, and material sold under this name is research chemical supply with unverified identity, purity, sterility and dose accuracy.
- The magnitude of exercise-induced increase in humans is small, and whether it is sufficient to produce the browning effects claimed is unresolved.
- No irisin product exists as a therapeutic, and supplements claiming to raise irisin have no controlled evidence.
- Human trials establishing any clinical benefit have not been conducted.
Sources
- PubMed research on irisin FNDC5 ELISA specificity controversy · NIH · National Library of Medicine
- DrugBank record for irisin · DrugBank
- Active clinical trials for irisin · U.S. National Library of Medicine
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Irisin FAQ
What is Irisin?
Irisin is a peptide cleaved from the membrane protein FNDC5 and released from muscle during exercise. It was proposed in 2012 as the mediator that converts white fat to brown, and its existence and importance have been contested ever since.
How does Irisin work?
Exercise increases PGC-1alpha, which raises FNDC5 expression; proteolytic cleavage releases irisin into the circulation. The original proposal was that irisin acts on white adipose tissue to induce UCP1 expression and a brown-fat-like thermogenic phenotype, and separately on bone and brain. The receptor was later identified as an integrin complex.
Is Irisin FDA approved?
No. Irisin is a research compound and not approved by the FDA for human use. Evidence level: preclinical. Evidence comes from animal or lab studies; effects in people are not established.
What is the half-life of Irisin?
Reported half-life: Short; not well characterised in humans.
How is Irisin taken?
Not available as a therapeutic; research use only.
What side effects have been reported with Irisin?
Reported in the sources: A substantial part of the early literature used commercial ELISA kits later shown to be non-specific, meaning many published irisin measurements were unreliable. This is one of the clearest recent cases of an assay artefact driving a field. No regulator has approved it, the human evidence base is limited, and material sold under this name is research chemical supply with unverified identity, purity, sterility and dose accuracy; The magnitude of exercise-induced increase in humans is small, and whether it is sufficient to produce the browning effects claimed is unresolved; No irisin product exists as a therapeutic, and supplements claiming to raise irisin have no controlled evidence; Human trials establishing any clinical benefit have not been conducted.
Educational summary compiled from the sources listed above. Not medical advice. Peptide Vault does not sell, source or recommend any compound. Talk to a qualified clinician before starting or changing anything.