How is IGF-1 LR3 different from regular IGF-1?

It has an added N-terminal peptide and an Arg-for-Glu substitution at position 3 that reduce binding to IGF-binding proteins, so more of it stays free and active, giving greater potency and a longer half-life in vitro.

What is IGF-1 LR3 actually used for?

Its legitimate use is in laboratories as a potent supplement to grow and study cells. Outside the lab it is encountered as a doping agent, which is prohibited in sport.

Is IGF-1 LR3 safe for humans?

There are no controlled human safety data. Based on IGF-1 biology, plausible risks include hypoglycemia, fluid retention, and concerns about abnormal tissue growth and cancer promotion; it is not intended for human use.

Is IGF-1 LR3 banned in sports?

Yes. IGF-1 and its analogs are prohibited by anti-doping authorities, and a body of analytical research focuses specifically on detecting their misuse in athletes.

Research chemical — not approved

IGF-1 LR3 — Complete Research Guide (2026)

Last updated 2026-06-30

TL;DR

IGF-1 LR3 is a peptide catalogued under Growth Hormone. Neutral reference entry; EU status: not approved for human use (research use only).

What is IGF-1 LR3?

IGF-1 LR3 (Long R3 IGF-1) is a modified insulin-like growth factor-1 with an added 13-amino-acid N-terminal extension and an Arg3 substitution that lowers its binding to IGF-binding proteins, increasing free potency and half-life.

It is not an approved medicine and has essentially no dedicated human clinical trials; it is marketed and used mainly as a laboratory cell-culture supplement and research reagent, and it appears in sport as a doping agent.

The evidence base below is therefore preclinical (cell-culture and animal) plus anti-doping literature, not human therapeutic trials.

How does IGF-1 LR3 work?

Long R3 IGF-1 activates the IGF-1 receptor to trigger PI3K/Akt and MAPK signaling that promotes cell proliferation, differentiation, and growth.

Its reduced IGFBP binding leaves more analog free to act, making it a potent reagent in vitro.

What does the research say about IGF-1 LR3?

In cell culture, Long R3 IGF-1 is a potent stimulus of myogenic (muscle) cell proliferation and is used as a reagent for that purpose. ^[4]
In animal infusion studies, Long R3 IGF-1 stimulated organ and tissue growth, illustrating its biological potency. ^[2]
It was engineered as a protease-resistant IGF-1 mutein, which is why it is favored as a stable research reagent. ^[1]

Clinical research & studies

The references below are the primary sources cited throughout this guide. Each links directly to PubMed or the regulator. Where evidence is preclinical (animal or in-vitro), that is stated rather than implied.

[1] Design and characterisation of long-R3-insulin-like growth factor-I muteins which show resistance to pepsin digestion — Bryant KJ et al., Growth Factors 1996. (In vitro / protein characterization)
[2] Long R3 insulin-like growth factor-I (IGF-I) infusion stimulates organ growth but reduces plasma IGF-I, IGF-II and IGF binding protein concentrations in the guinea pig — Conlon MA et al., The Journal of Endocrinology 1995. (Animal study)
[3] Long [R3] insulin-like growth factor-I reduces growth, plasma growth hormone, IGF binding protein-3 and endogenous IGF-I concentrations in pigs — Dunaiski V et al., The Journal of Endocrinology 1997. (Animal study)
[4] Effect of recombinant porcine IGFBP-3 on IGF-I and long-R3-IGF-I-stimulated proliferation and differentiation of L6 myogenic cells — Xi G et al., Journal of Cellular Physiology 2004. (In vitro / cell culture)
[5] The somatotropic axis in neonatal calves can be modulated by nutrition, growth hormone, and Long-R3-IGF-I — Hammon H et al., The American Journal of Physiology 1997. (Animal study)
[6] Insulin-like growth factor-I (IGF-I) misuse in athletes and potential methods for detection — Guha N et al., Analytical and Bioanalytical Chemistry 2013. (Review (anti-doping))

Dosing context

This is not medical advice or a usage recommendation. Dosing figures are reported research context only, cited from the published literature.

Because no human clinical trials define a therapeutic dose, no medical dosing exists; published quantities describe cell-culture concentrations or animal-model infusions only.

Any human dosing circulating online is unsanctioned and unsupported by clinical evidence.

Side effects & safety profile

There are no controlled human safety data for IGF-1 LR3; it is a research chemical, not an approved drug, and is prohibited in sport by anti-doping authorities.

Plausible risks extrapolated from IGF-1 biology include hypoglycemia, edema, and concerns about tissue overgrowth and cancer promotion.

It should not be used by humans; the literature reflects reagent and animal use plus doping detection, not medical treatment.

Stacking & combinations

Combining IGF-1 LR3 with other growth-promoting or hormonal agents is a doping and underground practice with no clinical evidence of safety or benefit and is prohibited in sport.

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Frequently asked questions

No. It is a research reagent and cell-culture supplement, not an approved medicine, and there are essentially no dedicated human clinical trials of IGF-1 LR3 itself.

References

[1] Design and characterisation of long-R3-insulin-like growth factor-I muteins which show resistance to pepsin digestion — Bryant KJ et al., Growth Factors 1996. PMID: 8919033. View sourceStudy: In vitro / protein characterizationCharacterizes the engineered Long R3 IGF-I analog, including its resistance to enzymatic digestion.
[2] Long R3 insulin-like growth factor-I (IGF-I) infusion stimulates organ growth but reduces plasma IGF-I, IGF-II and IGF binding protein concentrations in the guinea pig — Conlon MA et al., The Journal of Endocrinology 1995. PMID: 7561636. View sourceStudy: Animal studyInfused Long R3 IGF-I stimulated organ growth while lowering endogenous IGF and IGFBP levels in guinea pigs.
[3] Long [R3] insulin-like growth factor-I reduces growth, plasma growth hormone, IGF binding protein-3 and endogenous IGF-I concentrations in pigs — Dunaiski V et al., The Journal of Endocrinology 1997. PMID: 9488001. View sourceStudy: Animal studyLong R3 IGF-I altered the somatotropic axis and endogenous IGF/IGFBP levels in growing pigs.
[4] Effect of recombinant porcine IGFBP-3 on IGF-I and long-R3-IGF-I-stimulated proliferation and differentiation of L6 myogenic cells — Xi G et al., Journal of Cellular Physiology 2004. PMID: 15254966. View sourceStudy: In vitro / cell cultureLong R3 IGF-I stimulated proliferation of L6 muscle cells, used as a reagent to probe IGFBP-3 effects.
[5] The somatotropic axis in neonatal calves can be modulated by nutrition, growth hormone, and Long-R3-IGF-I — Hammon H et al., The American Journal of Physiology 1997. PMID: 9252489. View sourceStudy: Animal studyLong R3 IGF-I administration modulated the somatotropic axis in neonatal calves.
[6] Insulin-like growth factor-I (IGF-I) misuse in athletes and potential methods for detection — Guha N et al., Analytical and Bioanalytical Chemistry 2013. PMID: 23934394. View sourceStudy: Review (anti-doping)Reviews IGF-I misuse in sport and analytical strategies to detect it, the context in which LR3 analogs are abused.

This article is for educational and research purposes only. Peptides discussed here are not approved for human consumption by the FDA, EMA, or equivalent regulators outside of specific clinical contexts. Always consult a licensed medical professional before any therapeutic use.