IGF-1 LR3
Insulin-like growth factor-1 LR3 — long-acting analogue
A long-acting IGF-1 analogue used as a lab reagent and used illicitly for muscle growth. No human trials, serious hypoglycaemia risk, and a growth pathway linked to cancer.
- Category
- Growth & Performance
- Half-life
- Reported as substantially longer than native IGF-1, on the order of hours in preclinical summaries
- Cycle length
- Not established — no human protocol exists
- Level
- advanced
Overview
IGF-1 LR3 is an engineered version of insulin-like growth factor-1, the hormone growth hormone works through. The modification removes the binding site that normally ties IGF-1 to carrier proteins in the blood, meaning much more of a given dose stays free and active. This is a laboratory research reagent that migrated into bodybuilding use. It has never been approved, never been through a modern human trial, and it acts on one of the most fundamental growth pathways in the body. Unlike the growth hormone secretagogues, which nudge a regulated system, IGF-1 LR3 delivers an unregulated growth signal directly.
How it works
IGF-1 LR3 is a modified insulin-like growth factor-1 in which the binding region that normally holds it to carrier proteins has been altered, so far less of it is sequestered and more remains free to act. It binds IGF-1 receptors on muscle and other tissues, activating pathways that drive protein synthesis, cell growth and glucose uptake. The unbound fraction and the modified structure are why its action is both stronger and longer than the natural hormone's.
Reported benefits
- Substantially longer action than native IGF-1 in preclinical work
- Drives cell growth and protein synthesis in laboratory studies
- Used widely in cell-culture research
- Potent hypoglycaemic effect, which is also its main danger
Reported benefits describe what the published literature and user reports suggest — not a promise of outcome for any individual.
Dosing reference
There is no established human dose. Community-reported figures in the tens of micrograms per day are extrapolations from animal work and from studies of native IGF-1, and no controlled human trial of LR3 exists.
IGF-1 LR3 causes hypoglycaemia, which can be severe. Anyone using it — and no reputable clinical protocol does — would be handling a compound capable of driving blood glucose dangerously low with no monitoring in place.
Community-reported: 20–80 mcg per day by injection, split around training, in four-week cycles, with symptomatic low blood sugar reported more often at the higher end of that range.
These figures are what people report using in public communities. They have not been studied, verified or checked against certificates of analysis, and they are not a recommendation, a prescription or a target to aim for.
Where the reported amounts come from
Amounts are reproduced for education only. Doses from trials cannot be assumed to suit anyone else, and community-reported amounts are frequently wrong. Self-administering unapproved compounds carries serious risk.
The research picture
IGF-1 LR3 is a standard tool in cell culture and animal research, where it reliably stimulates cell proliferation and protein synthesis and produces rapid muscle growth in rodent models. Its extended half-life relative to native IGF-1 is precisely what makes it useful in the laboratory. That same property is the concern. IGF-1 signalling drives cell growth broadly, not only in muscle, and elevated IGF-1 is associated with several cancers in epidemiological studies. No human trial has examined LR3 itself. Anyone using it is administering a potent growth-factor analogue with no dose-finding data, no safety monitoring and a documented ability to cause hypoglycaemia.
Preclinical & non-clinical data
A long-acting analogue of IGF-1 with potent growth and cell-proliferation effects in animal models. Those same proliferation properties are the basis of the theoretical cancer-progression concern, which human data has never resolved.
Non-clinical data comes from cells and animals unless stated otherwise. It answers whether a compound is worth studying in people — not whether it is safe or effective in them.
What users report
This is the compound people describe feeling most acutely: intense muscle fullness and pumps within hours, and hypoglycaemia symptoms — shakiness, sweating, sudden hunger — that users learn to manage with food timing. Longer accounts mention joint pain, fatigue and, after repeated cycles, growth of the hands, feet or brow, which is why bodybuilders in these threads warn against using it the way they use peptides. Most of the caution in the reporting is about low blood sugar rather than anything else.
Where these reports come from
These are unverified personal accounts collected from public sources. They are not evidence of effectiveness or safety, they have not been independently checked, and they are not a recommendation to use anything described.
Possible side effects
- Hypoglycaemia, potentially severe
- Jaw, hand and foot discomfort from tissue growth
- Swelling and joint pain
- Fatigue
- Elevated IGF-1 with unknown long-term consequences
Safety notes
Serious hypoglycaemia is the acute risk and can be life-threatening. Because IGF-1 promotes cell proliferation, it is theoretically inadvisable in anyone with a history of malignancy or with proliferative conditions such as proliferative retinopathy. Organ growth — including cardiac and intestinal — is a documented concern in animal models at high exposure. Contraindicated conceptually in pregnancy. There is no established human dose at all.
Stacking
Often combined with growth hormone or insulin, both of which compound the hypoglycaemia risk. Combinations like this are the context in which severe adverse events are most often reported.
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