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 |