IGF-1 LR3

Dosing from the Literature

Published for muscle: nothing in people; the community doses come from online protocols, not trials (Dominikowski et al., 2026). Not published: any human dose of LR3.

No FDA-approved dose exists for IGF-1 LR3, and no peer-reviewed study reports a human dosing regimen (Dominikowski et al., 2026). The community rows are what online protocols describe; the mecasermin row is from the FDA label of a different molecule, native IGF-1. Not medical advice.

What It Is

IGF-1 LR3 (Long Arginine 3-IGF-1, also written LR3-IGF-1 or LongR³IGF-I) is a synthetic, recombinantly produced protein analog of human insulin-like growth factor-1 (IGF-1), engineered to bind less to IGF-binding proteins, IGFBPs (Francis et al., 1992). It is 83 amino acids in length compared to native IGF-1's 70, owing to a 13-amino-acid N-terminal extension (sequence MFPAMPLSSLFVN: the first 11 amino acids of methionyl pig growth hormone, then Val-Asn) and a single substitution at position 3 (glutamic acid → arginine, the "R3" in the name). The combined effect of these modifications: IGFBP-3 binding affinity is reduced approximately 1000-fold relative to native IGF-1. That does not make it last longer in the blood: in pigs, LR3 and similar variants were cleared faster than native IGF-1, though they lowered blood sugar for longer (Tomas et al., 1997).

IGF-1 LR3 was originally developed in the 1990s as a research reagent for cell culture media — a more stable IGF-1 variant for biotechnology applications including mammalian cell line cultivation, biopharmaceutical production, and laboratory growth-factor supplementation. It is sold by major life-sciences suppliers for these laboratory uses. Its application as an injectable for body composition, muscle growth, and recovery is entirely off-label community use that emerged from the bodybuilding and performance optimization scenes in the 2000s. There has never been a clinical pharmaceutical development program for IGF-1 LR3 itself in humans.

Critically, IGF-1 LR3 is not the same molecule as mecasermin (Increlex), the FDA-approved recombinant human IGF-1 marketed by Ipsen for severe primary IGF-1 deficiency in children. Mecasermin is identical in sequence to native human IGF-1 (70 amino acids, no R3 modification, no N-terminal extension) and is given to children twice daily (Increlex label). Mecasermin has rigorous regulatory approval and clinical trial backing; IGF-1 LR3 has neither. Collapsing the two into a single category — a frequent error in optimization-community literature — obscures the very different evidence bases.

Its appeal in online protocols is a single daily injection (Dominikowski et al., 2026), sold on the claim that it stays active much longer than native IGF-1 and so drives more muscle growth. The reality is more complicated: there is essentially no published clinical evidence in healthy human subjects, the hypoglycemia risk is meaningful (IGF-1 has insulin-mimetic activity at IGF-1R and partial cross-reactivity with the insulin receptor), and the GH/IGF-1-axis cancer-promotion concerns that apply to chronic GH-elevating compounds apply more directly here.

Mechanism of Action

IGF-1 LR3 acts on the IGF-1 receptor (IGF-1R), the same receptor as native IGF-1, but binds IGF-binding proteins much less (King et al., 1992; Francis et al., 1992). In pigs it was cleared from the blood faster than native IGF-1, yet lowered blood sugar for longer (Tomas et al., 1997).

• IGF-1R agonism (primary mechanism) — IGF-1R is a transmembrane receptor with built-in tyrosine kinase activity (Dominikowski et al., 2026), present on most cell types (Increlex label). When native IGF-1 binds it, the receptor activates IRS-1, PI3K and Akt, then mTOR, as well as the MAPK/ERK pathway: routes that influence protein synthesis, cell division and cell survival. LR3 binds the same receptor and is presumed to signal the same way; unlike the GHRPs, it does not work through the ghrelin receptor, GHSR-1a (Dominikowski et al., 2026).
• The IGFBP escape — the central pharmacologic difference — In blood, native IGF-1 is bound to six IGF-binding proteins, more than 80% of it in a complex with IGFBP-3 and an acid-labile subunit (Increlex label). These proteins regulate IGF-1's activity, blocking it in some settings and enhancing it in others (Wheatcroft & Kearney, 2009), and the more IGFBP-3 there is, the more slowly IGF-1 is cleared (Increlex label). LR3's Arg3 substitution and N-terminal extension cut its binding to these proteins, which made it more potent than native IGF-1 in rat muscle cells; in cells that made no binding proteins it was less potent (King et al., 1992; Francis et al., 1992).
• Half-life — Seller and guide pages give LR3 a half-life of 20–30 hours, but no study has documented its half-life in people (Dominikowski et al., 2026), and in pigs LR3 and similar variants were cleared from the blood faster than native IGF-1, though their effect on blood sugar lasted longer (Tomas et al., 1997). For mecasermin (native IGF-1) in children with severe IGF-1 deficiency, the label gives a half-life of 5.8 hours (Increlex label).
• PI3K/Akt — the anabolic signal — In mouse 3T3-L1 fat cells, native IGF-1 switched on PI3K and Akt (Assefa et al., 2017; PMC5750484). In rat L6 muscle cells, LR3 stimulated protein synthesis and slowed protein breakdown more potently than native IGF-1 (Francis et al., 1992).
• MAPK/ERK — the proliferative signal — In rat L6 muscle cells, LR3 stimulated DNA synthesis, a marker of cell division, more potently than native IGF-1 (Francis et al., 1992).
• Insulin receptor cross-reactivity (a proposed hypoglycemia mechanism) — The IGF-1 receptor is homologous to the insulin receptor (Increlex label), and IGFs can act through the insulin receptor: they did in H35 liver (hepatoma) cells, where LR3 kept its potency advantage over native IGF-1 (Francis et al., 1992). In mouse 3T3-L1 fat cells, LR3 raised glucose uptake at 20–100 nM, and an insulin-receptor blocker cut that effect while an IGF-1-receptor blocker did not (Assefa et al., 2017; PMC5750484). For the longer drop in blood sugar in pigs, the authors proposed action on liver insulin receptors or suppression of glucagon (Tomas et al., 1997).
• Glucose uptake (insulin-like) — The mecasermin label says IGF-1 suppresses the liver's glucose output and raises glucose use by other tissues, which gives it its blood-sugar-lowering potential, and that it inhibits insulin secretion (Increlex label). In mouse 3T3-L1 fat cells, native IGF-1 moved the glucose transporter GLUT-4 to the cell surface (Assefa et al., 2017; PMC5750484).
• Tissue effects — The mecasermin label describes IGF-1 driving bone growth at the growth plates, cell division in most tissues, and whole-body and organ growth in IGF-1-deficient rats (Increlex label).

What the Research Shows

The research base for IGF-1 LR3 specifically is dominated by cell culture and biopharmaceutical-process applications. Direct human clinical evidence is essentially absent. Native IGF-1 (mecasermin) has substantial human evidence; that evidence does not directly transfer to the LR3 form because of the pharmacokinetic differences.

• Cell culture / bioprocess research base (largest body of work) — IGF-1 LR3 is widely used as a growth factor supplement in mammalian cell culture media for biopharmaceutical production (CHO cell cultures, hybridoma cultures, stem cell maintenance). Its IGFBP-resistance and extended half-life are advantageous in serum-free media formulations. Hundreds of papers reference LR3 in this context.
• Animal hypertrophy studies (cell-line and rodent) — Multiple rodent studies have shown IGF-1 LR3 promotes skeletal muscle hypertrophy, accelerates muscle regeneration after injury, and supports satellite cell (muscle stem cell) activation. Dose-dependent effects on muscle fiber cross-sectional area are reproducible.
• Glucose uptake studies (3T3-L1 adipocytes; PMC5750484) — Comparative work showing IGF-1 LR3 induces dose-dependent glucose uptake in 3T3-L1 adipocytes — demonstrating the insulin-like activity that underpins the hypoglycemia risk.
• Native IGF-1 (mecasermin) human evidence (DOES NOT directly transfer to LR3) — Mecasermin (Increlex) has approval for severe primary IGF-1 deficiency in children based on multi-year clinical trials demonstrating linear growth promotion and metabolic effects. The label gives native rhIGF-1 under the skin twice daily, within 20 minutes of a meal or snack, with blood-sugar checks before meals until a well-tolerated dose is found (Increlex label). The evidence base is robust for the pediatric IGFD indication. Generalization to adult bodybuilding contexts is not supported.
• Mecasermin in HIV-associated wasting (older studies) — Native rhIGF-1 was investigated for HIV-related wasting; modest signal but not advanced beyond Phase 2/3 in this indication.
• Mecasermin combined with rhGH (recombinant human growth hormone — the injectable pharmaceutical version) — Combination protocols have been investigated for additional growth promotion in pediatric severe IGFD; modest additional benefit reported.
• No published human trial of IGF-1 LR3 specifically — A search of ClinicalTrials.gov for "IGF-1 LR3" or "LR3-IGF-1" returns no registered human trials as of April 2026. The optimization community use is entirely off-label and uncontrolled.
• Bodybuilding and athletic-use case reports — anecdotal only — Bodybuilding forums, podcasts, and practitioner reports describe LR3 use for muscle growth, recovery, and lean mass preservation in fat-loss phases. None of this constitutes clinical evidence; selection bias and reporting bias are large.
• Cancer / tumor-promotion theoretical concern — Chronic elevation of IGF-1 is epidemiologically associated with increased risk of certain cancers (colorectal, prostate, breast). IGF-1 LR3, as a sustained-action IGF-1R agonist, presents this concern more directly than transient GH-secretagogue use. The mechanism is biologically plausible: tumor cells express IGF-1R, and IGF-1R activation drives proliferation and resistance to apoptosis (programmed cell death).

Human Data

There is no published human trial of IGF-1 LR3 specifically. The closest available human evidence is for mecasermin (native rhIGF-1).

• Mecasermin (native rhIGF-1, FDA-approved as Increlex) — Approved 2005 for severe primary IGF-1 deficiency in children. In 76 children with severe IGF-1 deficiency treated for up to 12 years, height velocity rose from 2.8 to 8.0 cm a year in the first year, and hypoglycemia was the most common adverse event (Chernausek et al., 2007); the label says to give each dose within 20 minutes of a meal or snack (Increlex label).
• Mecasermin pediatric IGFD trial program (Ipsen / Tercica) — Multi-year trials supporting Increlex approval. Twice-daily SubQ dosing of native rhIGF-1; sustained linear growth response; well-characterized side-effect profile.
• HIV-associated wasting (mecasermin-related) — Investigated in older trials with modest signal; not advanced to approval for this indication.
• Native IGF-1 in adult muscle / aging — Some small studies have evaluated native IGF-1 effects in adult sarcopenia and aging contexts. Modest effects; not clinically transformative.
• No registered human trial of IGF-1 LR3 — A search of ClinicalTrials.gov returns nothing as of April 2026.
• Athletic doping detection studies — Multiple WADA-accredited laboratory papers establishing detection methods for IGF-1 analogs including LR3 in serum and urine. Detection is established and routine.
• No peer-reviewed human study — A 2026 review found no peer-reviewed human study of IGF-1 LR3 (Dominikowski et al., 2026).

Reconstitution & Storage

Seller and guide pages describe IGF-1 LR3 as a lyophilized (freeze-dried) powder, often in 1 mg vials.

• Acidic solvent — The cell-culture reagent's maker describes dissolving the powder in 100 mM acetic acid; guide pages describe 0.6% acetic acid, 10 mM hydrochloric acid, sterile water or bacteriostatic water. The Increlex (mecasermin) solution contains glacial acetic acid and sodium acetate at a pH of about 5.4 (Increlex label).
• Reconstitution technique — Seller and guide pages describe adding the liquid slowly down the vial wall and swirling or rolling the vial gently rather than shaking it. The mecasermin label says not to use a solution that is cloudy or contains particles (Increlex label).
• Storage — The cell-culture reagent's maker lists the freeze-dried powder as stable for five years at 2–8°C; guide pages list −20 to −80°C. For the mixed solution kept at 2–8°C, guide pages give anywhere from one to three weeks. The mecasermin label allows 30 days at 2–8°C after a vial is first opened and says to avoid freezing (Increlex label).

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Side Effects & Risks

The lines below come from animal studies of LR3 and from the label and trials of native IGF-1 (mecasermin), a different molecule.

• Hypoglycemia (low blood sugar) — In pigs, LR3 and similar variants lowered blood sugar 2–3 times more potently than native IGF-1 and kept it down longer (Tomas et al., 1997). Native IGF-1 (mecasermin) caused hypoglycemia in 49% of 76 children treated for up to 12 years, some of whom had it before treatment (Chernausek et al., 2007), and its label reports severe cases with seizures. The label lists the signs as dizziness, tiredness, restlessness, hunger, irritability, trouble concentrating, sweating, nausea and a fast or irregular heartbeat, and says severe hypoglycemia may cause unconsciousness, seizures or death (Increlex label).
• Theoretical cancer / tumor-promotion concern — IGF-1 influences cell growth and survival and is thought to matter in tumor development; in a 2004 meta-analysis of 21 studies, higher blood IGF-1 was associated with a modestly higher risk of prostate cancer and premenopausal breast cancer (Renehan et al., 2004). Cancers have been reported in children given native IGF-1 (mecasermin), more often at doses above the label's or with IGF-1 above the normal range; whether the drug caused them is unknown, and the label rules it out for children with a current or past cancer (Increlex label).
• Joint and limb pain — Joint pain (arthralgia) and pain in the arms or legs were each reported by 5% or more of the 71 children in the mecasermin trials (Increlex label).
• Headache, dizziness, convulsions and vomiting — Each was reported by 5% or more of the 71 children in the mecasermin trials (Increlex label).
• Increased intracranial pressure (intracranial hypertension) — Intracranial hypertension, with optic-disc swelling, visual changes, headache, nausea or vomiting, has occurred with mecasermin, in 3 of the 71 children in its trials (Increlex label).
• Tonsillar hypertrophy — Tonsil and adenoid enlargement was reported in 22% of 76 children on mecasermin (Chernausek et al., 2007); the label lists snoring, sleep apnea and middle-ear fluid among its complications (Increlex label).
• Allergic / immunogenic reaction — Part of LR3's sequence is not human: its 13-amino-acid extension comes mostly from pig growth hormone (Francis et al., 1992). Native IGF-1 (mecasermin) has caused allergic reactions ranging from injection-site reactions and hives to anaphylaxis requiring hospitalization, and anti-IGF-1 antibodies appeared in 14 of 23 children treated for two years, with no clinical effect seen (Increlex label).
• Drug interactions — The mecasermin patient information says the dose of insulin or other diabetes medicines may need to change (Increlex label).
• WADA banned (S2) — All IGF-1 forms banned at all times for tested athletes. Detection methods established. Any tested athlete using LR3 faces sanction.
• Sourcing risk — IGF-1 LR3 is an 83-amino-acid protein made by recombinant methods, in bacteria (Francis et al., 1992). Products sold online as research chemicals have uncertain purity, dose consistency and sterility (Dominikowski et al., 2026).

Quick Compare — IGF-1 LR3 vs Mecasermin vs IGF-1 DES vs MGF

Practical User Notes

• Athletes — banned — All IGF-1 forms banned by WADA at all times. Detection methods established. Not compatible with any anti-doping testing.

Bloodwork & Monitoring

No trial, label or guideline sets monitoring for IGF-1 LR3. For native IGF-1 (mecasermin), the label calls for blood-sugar checks before meals until a well-tolerated dose is found, eye (funduscopic) exams at the start and periodically, periodic checks for enlarged tonsils and adenoids, and watching for new tumors (Increlex label).

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Related Compounds

What IGF-1 LR3 users also compare with:

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References

1. Francis GL, Ross M, Ballard FJ, Milner SJ, Senn C, McNeil KA, Wallace JC, King R, Wells JR. Novel recombinant fusion protein analogues of insulin-like growth factor (IGF)-I indicate the relative importance of IGF-binding protein and receptor binding for enhanced biological potency. J Mol Endocrinol. 1992;8(3):213-223. PMID: 1378742. (Original IGF-1 LR3 design and characterization paper.)
2. Tomas FM, Walton PE, Dunshea FR, Ballard FJ. IGF-I variants which bind poorly to IGF-binding proteins show more potent and prolonged hypoglycaemic action than native IGF-I in pigs and marmoset monkeys. J Endocrinol. 1997;155(2):377-386. PMID: 9415072. (Demonstrates LR3 hypoglycemia potency.)
3. King R, Wells JR, Krieg P, Snoswell M, Brazier J, Bagley CJ, Wallace JC, Ballard FJ, Ross M, Francis GL. Production and characterization of recombinant insulin-like growth factor-I (IGF-I) and potent analogues of IGF-I, with Gly or Arg substituted for Glu3, following their expression in Escherichia coli as fusion proteins. J Mol Endocrinol. 1992;8(1):29-41. PMID: 1311930.
4. Francis GL, Aplin SE, Milner SJ, McNeil KA, Ballard FJ, Wallace JC. Insulin-like growth factor (IGF)-II binding to IGF-binding proteins and IGF receptors is modified by deletion of the N-terminal hexapeptide or substitution of arginine for glutamate-6 in IGF-II. Biochem J. 1993;293(Pt 3):713-719. PMID: 7688957. (Structure-activity work.)
5. IGF-1 LR3 — Wikipedia entry (April 2026). en.wikipedia.org/wiki/IGF-1_LR3. (Accessible reference summary; cites Francis 1992, Tomas 1997, and contemporary cell culture/research uses.)
6. Increlex (mecasermin) FDA Approval Documentation. FDA Approval Date: August 31, 2005. Sponsor: Tercica (now Ipsen). Indication: severe primary IGF-1 deficiency in children. (Native rhIGF-1; not IGF-1 LR3.)
7. Chernausek SD, Backeljauw PF, Frane J, Kuntze J, Underwood LE; GH Insensitivity Syndrome Collaborative Group. Long-term treatment with recombinant insulin-like growth factor (IGF)-I in children with severe IGF-I deficiency due to growth hormone insensitivity. J Clin Endocrinol Metab. 2007;92(3):902-910. PMID: 17192294. (Mecasermin pediatric efficacy and safety data.)
8. Cohen P, Bright GM, Rogol AD, Kappelgaard AM, Rosenfeld RG; American Norditropin Clinical Trials Group. Effects of dose and gender on the growth and growth factor response to GH in GH-deficient children: implications for efficacy and safety. J Clin Endocrinol Metab. 2002;87(1):90-98. PMID: 11788629. (rhGH + IGF-1 axis context.)
9. Ranke MB, Savage MO, Chatelain PG, Preece MA, Rosenfeld RG, Wilton P. Long-term treatment of growth hormone insensitivity syndrome with IGF-I. Results of the European Multicentre Study. Horm Res. 1999;51(3):128-134. DOI: 10.1159/000023345. (Mecasermin European data.)
10. Wheatcroft SB, Kearney MT. IGF-dependent and IGF-independent actions of IGF-binding protein-1 and -2: implications for metabolic homeostasis. Trends Endocrinol Metab. 2009;20(4):153-162. PMID: 19349193. (IGFBP biology — relevant to LR3's IGFBP escape.)
11. Insulin-Like Growth Factor (IGF) Binding Protein-2, Independently of IGF-1, Induces GLUT-4 Translocation and Glucose Uptake in 3T3-L1 Adipocytes. PMC5750484. (Demonstrates IGF-1 LR3 insulin-like glucose uptake activity.)
12. Brimson MA, Sodi R, et al. Hypoglycaemia and IGF-1: insulin-like growth factor effects on glucose homeostasis. Multiple reviews — collectively inform the central LR3 hypoglycemia risk.
13. Pollak MN. Insulin-like growth factor-related signalling and cancer development. Recent Results Cancer Res. 2007;174:49-53. PMID: 17302184. (Cancer / IGF-1 epidemiologic and mechanistic association.)
14. Renehan AG, Zwahlen M, Minder C, O'Dwyer ST, Shalet SM, Egger M. Insulin-like growth factor (IGF)-I, IGF binding protein-3, and cancer risk: systematic review and meta-regression analysis. Lancet. 2004;363(9418):1346-1353. PMID: 15110491. (Epidemiologic IGF-1/cancer association.)
15. Thomas A, Solymos E, Schänzer W, Thevis M. Determination of insulin-like growth factor-I and IGF analogues in human serum by liquid chromatography-tandem mass spectrometry. (WADA detection methods for IGF-1 forms including LR3.)
16. FDA. Bulk Drug Substances That Raise Significant Safety Risks (Category 2) Under Section 503A / 503B. FDA.gov. Updated 2025–2026. (IGF-1 LR3 is not listed.)
17. WADA Prohibited List 2026. World Anti-Doping Agency. wada-ama.org. (All IGF-1 forms banned under S2.)
18. Ipsen Pharmaceuticals. Increlex (mecasermin) Prescribing Information. (FDA-approved native rhIGF-1; not IGF-1 LR3.)
19. Stone W. The wellness world is eager for RFK Jr.’s promised move on peptides. NPR, March 31, 2026. npr.org/2026/03/31/nx-s1-5768206/peptides-rfk-fda-compounding-pharmacies. Read October 3, 2026. (The HHS secretary’s late-February podcast remarks, “about 14” peptides; reported, not a rule.)
20. FDA. Bulk Drug Substances Nominated for Use in Compounding Under Section 503A of the FD&C Act (503A categories list), versions updated April 15, April 22 and May 14, 2026. fda.gov/media/94155/download. Read October 3, 2026. (Notice that 12 peptides would leave Category 2 because their nominations were withdrawn; their removal; GHK-Cu, except injectable, back in Category 1.)
21. Dominikowski A, Rękoś Z, Olejarz M, Szczepanek-Parulska E, Domin R, Ruchała M. The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration. Front Endocrinol (Lausanne). 2026;17:1822475. doi:10.3389/fendo.2026.1822475. PMID: 42395176. (Online IGF-1 LR3 dosing protocols; no peer-reviewed human study of IGF-1 LR3.)
22. Eton Pharmaceuticals. Increlex (mecasermin) injection prescribing information. DailyMed set ID d5b2b0e1-c523-468d-9a0b-4ae4e4a8dbce, version effective May 18, 2026. dailymed.nlm.nih.gov. Read October 3, 2026. (Native rhIGF-1; not IGF-1 LR3.)

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