Irisin
Also known as: FNDC5 ectodomain, fibronectin type III domain-containing protein 5 cleavage product, FNDC5/irisin
Myokine / adipo-myokine hormone; proteolytic cleavage product of FNDC5 transmembrane protein
What it is
Irisin is a natural hormone your muscles release during exercise, nicknamed the 'exercise hormone.' Fitness enthusiasts, aging adults, and researchers studying metabolic health are interested in it because it may help with fat loss, bone strength, and brain function — essentially delivering some of exercise's benefits at a molecular level.
The scientific side
irisin is a hormone produced when the FNDC5 transmembrane protein is cleaved in response to exercise. This process is driven upstream by the PGC-1alpha transcriptional coactivator, which is activated during physical exertion, particularly aerobic and resistance training. Once secreted by skeletal muscle into circulation, irisin acts on multiple target organs through mechanisms that are still being characterized. In adipose tissue, irisin promotes the conversion of white fat toward a brown-fat-like phenotype, increasing energy expenditure and contributing to metabolic regulation, including improvements in glucose homeostasis and insulin sensitivity. In bone, irisin has been reported to promote osteogenesis by supporting osteoblast activity while suppressing osteoclastogenesis and oxidative stress, thereby protecting against bone loss. In the brain, irisin may cross or interact with the blood-brain barrier via mechanisms that may involve alphaVbeta5 integrin-mediated interactions, subsequently upregulating brain-derived neurotrophic factor (BDNF) expression. This irisin-BDNF signaling axis is proposed to enhance neuroplasticity, reduce amyloid-beta deposition, inhibit tau hyperphosphorylation, and suppress neuroinflammation, all of which are relevant to Alzheimer's disease pathology. Reviews note that irisin also modulates the NF-kB inflammatory pathway, reduces systemic oxidative stress, and activates AMP-activated protein kinase and MAPK signaling in reproductive tissues, with possible effects on testosterone production and spermatogenesis in rodent models of obesity-induced metabolic dysfunction. The receptor mediating irisin's actions in humans is not fully identified, and several studies caution that clinical evidence in humans is largely associative, with causality unestablished. Circulating irisin levels appear to be elevated in some disease states such as diabetic nephropathy, suggesting complex, context-dependent biology. Both aerobic and resistance exercise reliably raise serum irisin, with high-intensity intermittent exercise producing the largest acute increases observed in human trials.
Class: Myokine / adipo-myokine hormone; proteolytic cleavage product of FNDC5 transmembrane protein
Administration & storage
- Administration
- Intraperitoneal injection (preclinical rodent studies only)Subcutaneous injection (preclinical rodent studies only)Intravenous infusion (preclinical studies only)
- Storage
- Research-grade recombinant irisin: typically stored lyophilized at -20°C to -80°C, protected from light and repeated freeze-thaw cycles. Reconstituted solution stability varies by preparation; follow manufacturer's documentation.
Legal & regulatory status
Not approved as a drug or biologic. Irisin is not listed on any FDA approved product label. Sold only as a research chemical; not legal for human therapeutic use.
Not currently listed on the WADA Prohibited List. Status may change; athletes should verify with their sporting body before use.
No approved drug product containing irisin. Not authorized for human use in Canada.
What it's studied for
- Cognitive function and neuroprotection (Alzheimer's disease, aging-related cognitive decline) Preclinical + early human observational
- Metabolic syndrome and obesity (insulin resistance, fat browning, energy expenditure) Preclinical + human observational
- Bone health (osteoporosis, osteolysis prevention, sarcopenic obesity) Preclinical + early human observational
- Exercise-oncology and cancer biology (anti-proliferative, immune modulation) Preclinical + narrative review
- Male reproductive function (obesity-associated infertility, testosterone support) Preclinical only
- Neurodegenerative disease (Parkinson's disease, glymphatic clearance) Preprint / early preclinical
- Fibromyalgia (pain, cognitive symptoms, fibrofog) Small RCT
- Cardioprotection (doxorubicin-induced cardiotoxicity) Preprint / preclinical
Safety signals
- No human safety data from exogenous administration — risk profile entirely unknown
- Elevated circulating irisin associated with diabetic nephropathy in cross-sectional data
- Assay controversy and measurement unreliability — irisin detection inconsistencies
- Receptor unidentified in humans — mechanism of action and off-target risks unknown
- Potential modulation of HPG axis and gonadotropin regulation
- Altered bone remodeling coupling — possible context-dependent pro- or anti-resorptive effects
- Reduction in circulating irisin under genetic/disease conditions — supplementation effects in these contexts unknown
- No long-term safety data in any population
No peer-reviewed studies indexed for this peptide yet.
Frequently asked
Can I inject irisin to get the same benefits as exercise?
No human clinical trial has tested exogenous irisin injection for safety or efficacy. The research on irisin's benefits comes from studies measuring endogenous irisin raised by exercise, not from injecting it. The receptor through which irisin acts in humans has not been fully identified, meaning no one can reliably predict what exogenous administration would do — or how safe it would be.
How do I increase my irisin levels naturally?
Based on published studies, regular aerobic exercise and resistance training are the most consistently documented ways to raise circulating irisin. High-intensity intermittent exercise appears to produce larger acute increases than moderate-intensity continuous exercise. Three or more sessions per week over several weeks have been studied in human trials.
Is irisin banned in sport?
As of the data available, irisin does not appear on the current WADA Prohibited List. However, the regulatory landscape for peptide hormones and growth factors evolves. Athletes subject to anti-doping rules should check with their sport's governing body before using any research-grade peptide.
Does irisin help with Alzheimer's disease?
Animal and cell studies suggest irisin may reduce amyloid-beta toxicity, suppress neuroinflammation, and boost BDNF in the brain, which could theoretically slow Alzheimer's-related changes. However, there are no completed human trials testing irisin as an Alzheimer's treatment. Current evidence is preclinical. Exercise, which raises endogenous irisin, has more direct human evidence for cognitive benefit.
What does serum irisin tell me on a blood test?
Irisin measurement in blood is not a validated clinical diagnostic test. Researchers use ELISA-based assays, but there are no standardized reference ranges and significant controversy exists about assay accuracy. Elevated irisin has been observed in some disease states such as diabetic nephropathy, so a high value does not necessarily mean better health. Do not use commercial irisin tests to guide treatment decisions.
Will irisin help me lose weight or burn fat?
In mice, irisin promotes white-to-brown fat conversion and increases energy expenditure. In humans, the fat-browning effect of exercise-induced irisin is biologically plausible but has not been demonstrated in controlled weight-loss trials. There is no approved irisin-based weight loss product, and injecting research-grade irisin for fat loss has no human evidence base.