IGF-1 LR3
IGF-1 LR3 (Long R3 IGF-1) is an 83-amino-acid analogue of insulin-like growth factor 1 with an Arg substitution and an N-terminal extension that sharply reduce binding to IGF-binding proteins, giving a much longer half-life and higher free activity. It is a research reagent used in cell culture; human data for physique/performance use is essentially absent, and use is anecdotal.
01 Overview
The LR3 modifications keep the peptide free in circulation rather than bound to IGFBPs, so it is far more potent and longer-acting than native IGF-1. It was developed and is sold as a cell-culture supplement, not a medicine.
Bodybuilding use aims to exploit IGF-1's proliferative and anabolic signalling for muscle growth, but there are no controlled human trials at physique doses. Because IGF-1 is mitogenic, the main theoretical concerns are hypoglycaemia and stimulation of pre-existing neoplasia. Ratings here reflect mechanism and anecdote, not clinical evidence.
02 Mechanism
Activates the IGF-1 receptor to trigger PI3K/Akt and MAPK signalling, driving protein synthesis, myoblast proliferation and anti-apoptotic effects; the LR3 modification minimises IGFBP binding so more peptide is active for longer.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Anecdotal (non-medical) | 20–50 mcg/day | SubQ | No clinical basis; ranges are from anecdote only. Hypoglycaemia risk. |
| Higher anecdotal | 50–100 mcg/day | SubQ | Escalating hypoglycaemia risk; unmonitored use. |
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Muscle-cell proliferation and hypertrophyIGF-1 signalling promotes myoblast proliferation and protein synthesis in vitro and in animals; human physique data lacking. | Preclinical | ||
| Nutrient partitioning / anabolismUsers report improved pumps and recovery; not established in controlled human studies. | Anecdotal |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| HypoglycaemiaIGF-1 has insulin-like activity and can drop blood glucose, sometimes sharply. | Severe | Common at higher doses | Anecdotal | |
| Theoretical tumour promotionIGF-1 is mitogenic and anti-apoptotic; sustained elevation could promote growth of existing malignancies. | Severe | Unknown, mechanistic concern | Preclinical | |
| Injection-site reactionsLocal redness, swelling or lump at subcutaneous injection sites. | Mild | Common | Anecdotal |
06 Commonly used with
What igf-1 is combined with, and why. This is about intent rather than safety — the interactions table below covers what is dangerous. Nothing here is listed without what it costs.
| Compound | Frequency | Purpose & trade-off |
|---|---|---|
| Stacked compounds | ||
| SomatropinHGH | IGF-1 LR3 is most often run with GH so the GH provides systemic and lipolytic effects while the long-acting IGF-1 supplies a sustained direct anabolic signal.Trade-off: Both lower blood glucose, so the combination markedly raises hypoglycaemia risk, and layering two growth-promoting agents amplifies the theoretical tumour-growth concern with no human safety data. | |
| Insulinperi-workout | Used in advanced protocols to maximise nutrient partitioning, since insulin and IGF-1 act on related pathways to drive glucose and amino acids into muscle.Trade-off: Two glucose-lowering agents together create a serious, potentially life-threatening hypoglycaemia hazard and demand carbohydrate management that many users get wrong. | |
| Testosteronebase cycle | Run on an anabolic base so androgen-driven protein synthesis complements IGF-1's local hypertrophic and satellite-cell effects.Trade-off: You take on the full androgenic side-effect and suppression profile while still carrying IGF-1's hypoglycaemia and growth-signalling unknowns. | |
| Support & ancillaries | ||
| Fast carbohydrates on handhypo rescue | Simple sugars are kept available to reverse the acute blood-sugar drops IGF-1 LR3 can cause after dosing.Trade-off: It is only reactive damage control — it does not prevent hypoglycaemic episodes and encourages a false sense of safety around a genuinely risky compound. | |