IGF-1 LR3
Muscle Building, Performance
In short
- A modified form of insulin-like growth factor 1 with an arginine substitution and a 13-amino-acid N-terminal extension.
- The modifications drastically reduce binding to IGF binding proteins, extending its half-life from minutes to many hours and greatly increasing potency.
- That extended activity is the entire point and also the entire risk — IGF-1 is a growth factor, and unbound IGF-1 acts on every tissue.
- No human trial of IGF-1 LR3 exists. Recombinant IGF-1 (mecasermin) is approved for severe IGF-1 deficiency and provides the relevant safety precedent.
- Prohibited at all times in sport under WADA class S2.
Structure
An 83-amino-acid modified protein. PubChem has no entry under this research-market name, and proteins of this size are represented by sequence and structural coordinates rather than a small-molecule diagram.
How it works
IGF-1 mediates most of growth hormone's anabolic effects. In circulation the great majority is bound to IGF binding proteins, which regulate availability and half-life.
LR3 modifications — Arg substituted at position 3, plus a 13-residue N-terminal extension — sharply reduce binding protein affinity. The result is a molecule that stays free and active far longer than native IGF-1, with a half-life measured in hours rather than minutes.
Signalling through the IGF-1 receptor activates PI3K/Akt and MAPK pathways, driving protein synthesis, cell proliferation, and inhibition of apoptosis.
What the research shows
No human trial of IGF-1 LR3 has been conducted.
Mecasermin, recombinant human IGF-1, is FDA-approved for severe primary IGF-1 deficiency and demonstrates that IGF-1 signalling produces growth in that population, along with a clear side-effect profile dominated by hypoglycaemia.
Claims of muscle hyperplasia and localised growth from research-market IGF-1 LR3 are not supported by any human study.
Dosing in the literature
Figures below are quoted from published studies, with the species or population they were measured in. They are records of what was studied, not recommendations.
| Studied in | Amount | Route | Source |
|---|---|---|---|
| Human — mecasermin (recombinant IGF-1), approved label for severe IGF-1 deficiency | 40–120 µg/kg twice daily, with food | subcutaneous | FDA label |
Commonly reported ranges
These are amounts people report using. They are not from any study, have not been evaluated for safety, and are reproduced here only because they circulate widely and are better seen alongside the evidence than instead of it.
| Reported by | Amount | Route |
|---|---|---|
| Commonly reported | 20–50 µg daily | subcutaneous |
No published human pharmacokinetic study establishes a dose, interval, or duration for this compound. Community figures below have no trial behind them and are reports of practice, not evidence. The mecasermin label is for a different molecule with far shorter activity, and its dosing instructions include eating within 20 minutes specifically because of hypoglycaemia risk. LR3's longer activity makes that consideration larger, not smaller.
Handling and storage
Supplied as a lyophilised powder requiring reconstitution with bacteriostatic water. The powder is comparatively stable; once reconstituted it is refrigerated and used within weeks. Track the date you reconstitute each vial — the Inventory section does this, and it is the difference between knowing a vial is three weeks old and guessing.
IGF-1 LR3 is reported to be sensitive to handling and degradation. Subcutaneous injection is the community route.
The hypoglycaemia consideration means food timing is not optional — the approved IGF-1 product requires a meal within 20 minutes of dosing.
Side effects
Hypoglycaemia is the primary and immediate risk. IGF-1 has meaningful cross-reactivity with the insulin receptor, and the mecasermin label carries hypoglycaemia as its dominant adverse effect with explicit food-timing instructions.
Other effects documented for mecasermin include tonsillar hypertrophy, injection-site lipohypertrophy, and intracranial hypertension.
The long-term concern is proliferative. IGF-1 signalling inhibits apoptosis and drives cell proliferation, and epidemiological work has associated higher circulating IGF-1 with increased risk of several cancers. Deliberately elevating free IGF-1 with a modified long-acting analogue is the most direct version of that exposure available in this library.
Combinations
Commonly combined with GH secretagogues, which raise endogenous IGF-1 — compounding the same signal from two directions.
With insulin, the hypoglycaemia risk is additive and serious.
Research status
IGF-1 biology is extensively studied and mecasermin is approved. IGF-1 LR3 specifically was developed as a cell-culture reagent, which is what it is sold as, and has no human clinical literature.
Legal status
Not approved for human use in any jurisdiction. Sold as a laboratory reagent for cell culture. Recombinant IGF-1 (mecasermin) is prescription-only where marketed.
WADA status
PROHIBITED AT ALL TIMES under WADA class S2 — growth hormone secretagogues, their releasing factors and mimetics are explicitly named. Any tested athlete should treat this as an anti-doping violation.
Conclusion
IGF-1 LR3 was engineered to keep a potent growth factor active and unregulated in circulation. Everything attractive about that and everything concerning about it are the same property.
The acute risk is hypoglycaemia and it is real and immediate. The long-term question concerns proliferation, and nobody has answered it.
Sources
Track your own IGF-1 LR3 protocol
Peppers logs your doses, models your levels from this half-life, tracks your vials and tells you when you will run out. Free on iPhone.
Reference and educational information only. Not medical advice. Nothing here diagnoses, treats, or prescribes, and nothing here is a recommendation to use any compound. The compounds described are research chemicals and are not approved for human consumption. Legal and anti-doping status change — the review date above is when these claims were last checked. Talk to a qualified clinician about anything you intend to take.