IGF-1 LR3: what the research shows
- By Reed Calder
- Last reviewed Nov 11, 2026
- 24 studies and official documents checked
In short
IGF-1 LR3 is a lab-made, longer version of IGF-1, the hormone that carries much of growth hormone’s effect. It was changed so the proteins that normally hold IGF-1 back can’t grab it. It has been tested in rats, guinea pigs, pigs, monkeys and sheep, and we found no published study of it in people. In food-restricted rats it kept weight up but didn’t save muscle protein. It isn’t FDA-approved, the FDA has told a compounder that products made from it don’t qualify for the compounding exemption, and it’s banned in sport. The only approved IGF-1 drug warns of severe low blood sugar and cancers.
EvidenceCellAnimalHuman
IGF-1 LR3 is sold online and by some clinics for muscle growth, recovery and fat loss. It is a protein, not a steroid. This page covers what it is, what animal studies found, the safety signals, what lab tests of seized and black-market vials found, and where it stands legally.
Names and forms you’ll see
| Name | What it is | Studied in people? |
|---|---|---|
| IGF-1 LR3, LR3-IGF-I, Long R3 IGF-I | A lab-made form of IGF-1 with 83 amino acids; natural IGF-1 has 70 (FDA GSRS) | No published study found |
| IGF-1, mecasermin (Increlex) | Human IGF-1, made by recombinant DNA. The only IGF-1 the FDA has approved: for children with severe primary IGF-1 deficiency (Increlex label, 2025) | Yes, in children with the deficiency |
| des(1-3)IGF-1, “IGF-1 DES” | A different variant, with three amino acids cut from the front. Short card: IGF-1 DES | No published study found |
| His-tagged Long R3 IGF-I | A lab-reagent version with a six-histidine tag added for purification, found in a seized injection vial (Kohler et al., 2010) | No |
CAS numbers
A CAS number is a substance’s chemical registry number. Some “research” vials list it in place of a name. A different number usually means a different form, such as a salt, or a different substance. Two CAS numbers are on file for mecasermin; the table shows the one GSRS lists first.
What IGF-1 LR3 is
IGF-1 (insulin-like growth factor 1) is a hormone that growth hormone prompts the liver and other tissues to make. It acts on cells through the IGF-1 receptor (Increlex label, 2025). In the blood, IGF-binding proteins bind it and shape how much reaches tissues (Bastian et al., 2000).
IGF-1 LR3 has two changes: the amino acid at position 3 is arginine instead of glutamic acid, and an extra stretch of 13 amino acids sits at the front, copied from the start of pig growth hormone, for a total of 83 amino acids (Francis et al., 1992; King et al., 1992). Together they make it bind the binding proteins poorly. In lab tests it also binds the IGF-1 receptor about three times less tightly than IGF-1, yet in rats it was about 2.5 times as potent at restoring weight (Tomas et al., 1992). The idea is that more of the dose is free to act. That is also why it behaves differently from natural IGF-1 in the studies below.
What has been studied
In people
- No published study of IGF-1 LR3 in people. PubMed lists about 140 papers that name it; they are animal and cell studies, farm-animal research and anti-doping lab work. ClinicalTrials.gov has no record for it (searched November 11, 2026).
- A 2026 clinical review of growth hormone and IGF-1 peptides sold as “research compounds”, including IGF-1 LR3, lists problems reported by people who self-inject them across the group: blood sugar changes, fluid retention, joint and muscle pain, and injection-site reactions. It calls the cell-growth (mitogenic) concerns “biologically plausible but unproven” (Dominikowski et al., 2026).
EvidenceCellAnimalHuman
In animals
- Rats given a catabolic steroid. Over 7 days, IGF-1 variants including LR3 were about 2.5 times as potent as IGF-1 at reversing weight and nitrogen loss (Tomas et al., 1992). In diabetic rats the variants were 2.5 to 3 times as potent at restoring growth, and raised muscle protein-making by up to 50%, with IGF-1 itself the weakest (Tomas et al., 1993).
- Food-restricted rats. A week of LR3 kept body weight 3 to 8% higher but didn’t save muscle protein. In adult rats it made protein breakdown worse (Tomas, 2001).
- Pigs and marmoset monkeys. IGF-1 variants, LR3 among them in the pigs, lowered blood sugar 2 to 3 times more strongly than IGF-1, and the effect lasted longer: over four hours the total drop was 4 to 8 times as large (Tomas et al., 1997).
- Organ growth. In young rats, a week of infusion of IGF-1 or LR3 raised kidney weight by up to 85% and spleen weight by up to 76%, and LR3 was the more potent (Steeb et al., 1997). In guinea pigs, LR3 made the adrenals, gut, kidneys and spleen heavier but didn’t speed overall growth (Conlon et al., 1995).
- Piglets. In artificially reared newborn pigs fed freely, LR3 raised daily weight gain in the second half of the study (457 vs 386 g a day) but did nothing in pigs on limited feed (Dunshea et al., 2002).
- Monkeys. IGF-1 raised a binding protein, IGFBP-3, in adolescent rhesus monkeys; LR3 did not (Wilson et al., 2000).
- Fetal sheep. In growth-restricted fetal sheep, a week of LR3 didn’t change body weight. The same lab’s earlier study in normal fetal sheep found it raised weight but lowered insulin (White et al., 2025).
EvidenceCellAnimalHuman
The usual claims, checked
| Claim | What the studies found |
|---|---|
| Builds muscle | In food-restricted rats LR3 kept weight but not muscle protein (Tomas, 2001). In diabetic rats the variants raised muscle protein-making (Tomas et al., 1993). No study in people |
| Stays active 20 to 30 hours | We found no study behind this figure. In rats given one dose, labeled LR3 left the blood faster than labeled IGF-1 (Bastian et al., 2000). In pigs, the blood-sugar effect of LR3 and other variants lasted longer (Tomas et al., 1997) |
| About 3 times as potent as IGF-1 | In rats and pigs the variants were 2 to 3 times as potent for growth and blood sugar (Tomas et al., 1992; Tomas et al., 1997). Potency in people is unknown |
| Burns fat | In young food-restricted rats LR3 raised fat loss (Tomas, 2001). No study in people |
| Raises testosterone | We found no study that measured it |
| A safe “natural” alternative to steroids | It isn’t a steroid, and it isn’t natural: it is a lab-made protein. The approved IGF-1 drug carries warnings for severe low blood sugar and for neoplasms (Increlex label, 2025) |
What the studies used
| Study | Animal | How given | Length |
|---|---|---|---|
| Tomas 1992 | Rats on a catabolic steroid | Infusion by implanted pump | 7 days |
| Tomas 1993 | Diabetic rats | Infusion by implanted pump | 7 days |
| Tomas 1997 | Pigs and marmosets | One injection | 4 hours of blood samples |
| Tomas 2001 | Young and adult rats on limited food | Continuous infusion | 7 days |
| Steeb 1997 | Newborn rats | Infusion by implanted pump | 6.5 days |
| Conlon 1995 | Guinea pigs | Continuous infusion | 7 days |
| Dunshea 2002 | Newborn pigs | Continuous infusion | 8 to 18 days |
| White 2025 | Fetal sheep | Continuous infusion | 1 week |
These are the studies’ methods, not a dose for anyone to use. Animals were given IGF-1 LR3 by pump, mostly for a week. Nobody has tested it in people.
Side effects and safety
- There are no human safety data for IGF-1 LR3. What follows comes from animals and from the approved IGF-1 drug, which is a different protein.
- Low blood sugar. In pigs and marmosets, IGF-1 variants (LR3 among them in pigs) lowered blood sugar 2 to 3 times more strongly than IGF-1 and for longer (Tomas et al., 1997). The approved drug, mecasermin, warns that severe low blood sugar, with seizures, has occurred (Increlex label, 2025).
- Organ growth. Kidneys, spleen, gut and adrenals grew in rats and guinea pigs (Steeb et al., 1997; Conlon et al., 1995). The mecasermin label lists enlarged tonsils and adenoids, raised pressure inside the skull, and slipped hip bones in children.
- Cancer. The mecasermin label reports cancers in children on treatment, mostly in children already at high risk and more often at above-recommended doses or high IGF-1 levels, and says it is unknown whether treatment played a role (Increlex label, 2025). Separately, a review of 21 studies found that people with higher natural IGF-1 levels had a modestly higher risk of prostate and premenopausal breast cancer (Renehan et al., 2004). That is about natural levels, not this product.
- Muscle protein. In adult food-restricted rats, LR3 increased muscle protein breakdown (Tomas, 2001).
- Product quality. An anti-doping lab found a lab-reagent version with a purification tag in a black-market injection vial (Kohler et al., 2010), and later found unpurified LR3 in confiscated products (Kohler et al., 2010). Black-market LR3 also contained damaged, oxidized forms (Mongongu et al., 2021).
- Unstudied. Long-term use, use in people with diabetes or cancer history, interactions, and use in pregnancy.
Side effects people report from online products aren’t covered here; they come from users, not studies.
Legal and approval status
- Not FDA-approved. The only approved IGF-1 is mecasermin (Increlex), for children with severe primary IGF-1 deficiency or with growth hormone gene deletion who have made antibodies to growth hormone (Increlex label, 2025). IGF-1 LR3 is a different protein.
- Not eligible for the compounding exemption. In an April 1, 2020 warning letter, the FDA named IGF1-LR3 among 22 substances a compounder had used and said products made from them don’t qualify: they have no U.S. drug standard, aren’t part of an approved drug and aren’t on the list of bulk substances pharmacies may compound (FDA warning letter, 2020).
- Not on the FDA’s safety-risk page, which covers other peptides (FDA, 2026). That is not approval.
- Not in the October 2026 HHS policy. That temporary policy covers six other peptides (Reuters, 2026).
- Banned in sport. The World Anti-Doping Agency’s 2026 list prohibits IGF-1 and its analogues among growth factors (WADA, 2026). Anti-doping labs have built tests for IGF-1 LR3 because it is sold on the black market (Mongongu et al., 2021).
- “Research use only” products aren’t approved for use in people.
What to look for if you research it
We don’t name or link sellers. These checks come from the registry and the lab studies:
- 83 amino acids, and the right sequence. The GSRS sequence starts MFPAMPLSSLFVNGPRTLCGAELV and ends PLKPAKSA (FDA GSRS). A different length, or a tag on the end, means a different product (Kohler et al., 2010).
- The CAS number on the certificate. GSRS lists 143045-27-6 for IGF-1 LR3. The approved drug, mecasermin, is a different substance with its own numbers.
- Signs of damage. Black-market products had oxidized forms of the peptide, which a plain purity percentage may not show (Mongongu et al., 2021).
Our guide to what to look for explains what each test on a lab report proves and which routes are legal; how to read a peptide study explains how to judge the studies sellers cite.
What’s still unknown
- Whether it does anything useful for muscle, recovery or fat loss in people.
- How long it lasts in people, and how that compares with natural IGF-1.
- How it affects blood sugar, organ size and cancer risk in people.
- Whether any dose is safe, and what happens over months or years.
- What is really in the vials sold online.
Retracted and flagged studies
A retracted study has been pulled by its journal, usually for serious errors or misconduct, and its results shouldn’t be relied on. A withdrawn paper was pulled, often before final publication. An expression of concern means the journal has flagged a problem it is still looking into.
We check every study this page cites against PubMed and the Retraction Watch database, and search both for flagged studies that mention IGF-1 LR3. We recheck every month. Last checked Nov 11, 2026.
We found no retracted, withdrawn or flagged studies that mention IGF-1 LR3.
Studies this page relies on
| Study | Published in | Status |
|---|---|---|
| King et al., 1992 | J Mol Endocrinol | No retraction or concern |
| Tomas et al., 1992 | Biochem J | No retraction or concern |
| Francis et al., 1992 | J Mol Endocrinol | No retraction or concern |
| Conlon et al., 1995 | J Endocrinol | No retraction or concern |
| Tomas et al., 1993 | Biochem J | No retraction or concern |
| Steeb et al., 1997 | Am J Physiol | No retraction or concern |
| Tomas et al., 1997 | J Endocrinol | No retraction or concern |
| Bastian et al., 2000 | J Endocrinol | No retraction or concern |
| Wilson and Lackey, 2000 | Growth Horm IGF Res | No retraction or concern |
| Tomas, 2001 | Growth Horm IGF Res | No retraction or concern |
| Dunshea et al., 2002 | Br J Nutr | No retraction or concern |
| Renehan et al., 2004 | Lancet | No retraction or concern |
| Liu et al., 2008 | Ann Intern Med | No retraction or concern |
| Kohler et al., 2010 | Growth Horm IGF Res | No retraction or concern |
| Kohler et al., 2010 | Drug Test Anal | No retraction or concern |
| Mongongu et al., 2021 | Drug Test Anal | No retraction or concern |
| White et al., 2025 | Am J Physiol Endocrinol Metab | No retraction or concern |
| Dominikowski et al., 2026 | Front Endocrinol (Lausanne) | No retraction or concern |
Bring your questions to other researchers
Our forum opens once 100 researchers join the waitlist. Members post studies, ask what they actually found, and answer with sources.
Questions
What is IGF-1 LR3?
A lab-made form of IGF-1 with 83 amino acids instead of 70, changed so IGF-binding proteins hold it poorly (Francis et al., 1992). It isn’t approved for any use.
How long does IGF-1 LR3 last?
We found no study in people. In rats given one dose, labeled LR3 left the blood faster than IGF-1 (Bastian et al., 2000), while in pigs the blood-sugar effect of LR3 and other variants lasted longer (Tomas et al., 1997). Figures like “20 to 30 hours” online have no study behind them that we found.
Does IGF-1 increase blood sugar?
It does the opposite: IGF-1 and its variants lower blood sugar, and in pigs and marmosets the variants did so 2 to 3 times more strongly (Tomas et al., 1997). The approved IGF-1 drug warns of severe low blood sugar (Increlex label, 2025).
Is IGF-1 good for muscle building?
Not shown in people. In food-restricted rats, LR3 didn’t save muscle protein (Tomas, 2001). For growth hormone, a pooled analysis found more lean mass but no strength gain (Liu et al., 2008).
Is IGF-1 LR3 better than HGH?
No study compared them. Growth hormone prompts the body to make its own IGF-1 (Increlex label, 2025); IGF-1 LR3 is a lab-made variant that acts on the IGF-1 receptor. Neither is shown to build strength in healthy adults (Liu et al., 2008 for growth hormone).
Does IGF-1 LR3 raise testosterone?
We found no study that measured it.
Is IGF-1 a steroid?
No. IGF-1 is a protein hormone, and IGF-1 LR3 is a lab-made protein of 83 amino acids (FDA GSRS). Anti-doping rules treat it as a growth factor.
What are the side effects of IGF-1 LR3?
No human studies exist. Animal studies show low blood sugar and larger organs (Tomas et al., 1997; Steeb et al., 1997). The approved IGF-1 drug lists low blood sugar, swollen tonsils, skull pressure and cancers (Increlex label, 2025).
What is the IGF-1 LR3 dosage?
No dose comes from a study in people. Animal studies gave it by pump, mostly for a week (Tomas, 2001). Online charts and “cycles” aren’t evidence.
Is IGF-1 LR3 legal?
It isn’t FDA-approved, the FDA has said products made from it don’t qualify for compounding (FDA warning letter, 2020), and it’s banned in sport (WADA, 2026). Our guide to what to look for covers the routes people use.
Where can I get IGF-1 LR3 online?
Sellers offer it, but it has no approved use and lab tests found wrong or damaged products (Mongongu et al., 2021). We don’t link sellers; see what to look for.
What is the difference between IGF-1 LR3 and IGF-1 DES?
Both bind binding proteins poorly. DES(1-3) has three amino acids removed from the front; LR3 has one changed and 13 added. Details are on the IGF-1 DES card.
Sources
- Francis GL, et al. 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):213-23. PubMed 1378742
- King R, et al. 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. PubMed 1311930
- Tomas FM, et al. Insulin-like growth factor-I (IGF-I) and especially IGF-I variants are anabolic in dexamethasone-treated rats. Biochem J. 1992;282(Pt 1):91-7. PubMed 1371669
- Tomas FM, et al. Insulin-like growth factor-I and more potent variants restore growth of diabetic rats without inducing all characteristic insulin effects. Biochem J. 1993;291(Pt 3):781-6. PubMed 7683875
- Tomas FM, et al. 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):377-86. PubMed 9415072
- Tomas FM. Insulin-like growth factor-I (IGF-I) analogue, LR(3)IGF-I, ameliorates the loss of body weight but not of skeletal muscle during food restriction. Growth Horm IGF Res. 2001;11(2):92-103. PubMed 11472075
- Steeb CB, et al. Systemic infusion of IGF-I or LR(3)IGF-I stimulates visceral organ growth and proliferation of gut tissues in suckling rats. Am J Physiol. 1997;272(3 Pt 1):G522-33. PubMed 9124573
- Conlon MA, et al. 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. J Endocrinol. 1995;146(2):247-53. PubMed 7561636
- Dunshea FR, et al. Insulin-like growth factor-I and analogues increase growth in artificially-reared neonatal pigs. Br J Nutr. 2002;87(6):587-93. PubMed 12067429
- Wilson ME, et al. IGF-I but not the IGF-I variant long R(3)IGF-I increases serum IGFBP-3 in adolescent monkeys. Growth Horm IGF Res. 2000;10(1):37-44. PubMed 10753591
- White A, et al. IGF-1 LR3 does not promote growth in late-gestation growth-restricted fetal sheep. Am J Physiol Endocrinol Metab. 2025;328(1):E116-25. PubMed 39679943
- Bastian SE, et al. Transport of circulating IGF-I and LR3IGF-I from blood to extracellular wound fluid sites in rats. J Endocrinol. 2000;164(1):77-86. PubMed 10607940
- Kohler M, et al. Detection of His-tagged Long-R³-IGF-I in a black market product. Growth Horm IGF Res. 2010;20(5):386-90. PubMed 20675162
- Kohler M, et al. Confiscated black market products and nutritional supplements with non-approved ingredients analyzed in the Cologne Doping Control Laboratory 2009. Drug Test Anal. 2010;2(11-12):533-7. PubMed 21204286
- Liu H, et al. Systematic review: the effects of growth hormone on athletic performance. Ann Intern Med. 2008;148(10):747-58. PubMed 18347346
- Mongongu C, et al. Detection of LongR3-IGF-I, Des(1-3)-IGF-I, and R3-IGF-I using immunopurification and high resolution mass spectrometry for antidoping purposes. Drug Test Anal. 2021;13(7):1256-69. PubMed 33587816
- Dominikowski A, et al. 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. PubMed 42395176
- Renehan AG, et al. Insulin-like growth factor (IGF)-I, IGF binding protein-3, and cancer risk: systematic review and meta-regression analysis. Lancet. 2004;363(9418):1346-53. PubMed 15110491
- Ipsen Biopharmaceuticals. Increlex (mecasermin) injection, prescribing information, label version 21, effective August 5, 2025. DailyMed
- U.S. Food and Drug Administration. Warning letter to Tailor Made Compounding LLC, MARCS-CMS 594743, April 1, 2020. FDA letter
- U.S. Food and Drug Administration. Safety risks associated with certain bulk drug substances nominated for use in compounding. Content current as of April 22, 2026. FDA page
- ClinicalTrials.gov search for IGF-1 LR3, LR3 IGF and long R3 IGF-I, November 11, 2026: no registered studies. Search
- World Anti-Doping Agency. 2026 Prohibited List (S2, growth factors: IGF-1 and its analogues). WADA document
- Reuters. U.S. health department to allow temporary sale of some unapproved peptides. October 28, 2026. Article
- U.S. Food and Drug Administration. Global Substance Registration System: Long-(Arg3)insulin-like growth factor-I (UNII M9L22Y19H9). GSRS
- U.S. Food and Drug Administration. Global Substance Registration System: Mecasermin (UNII 7GR9I2683O). GSRS
Last reviewed Nov 11, 2026. Approval and compounding status change often; we recheck this page when they do. Nothing here is medical advice; see our medical disclaimer. Found a mistake? Email editors@peptideresearchstudy.com.