IGF-1 LR3: what it is, what the studies show and where it stands
IGF-1 LR3 (Long [Arg3]-IGF-I) is a laboratory-made analog of human IGF-1: the IGF-1 chain with arginine in place of glutamate at position 3 and an extra 13 amino acid piece on the front end. It binds the body's IGF binding proteins only weakly.
At a glance
US Not approved
Canada Not authorized
Group Growth hormone
Sources 16
Checked 10 Oct 2026What is IGF-1 LR3?
IGF-1 LR3 (Long [Arg3]-IGF-I) is a laboratory-made analog of human IGF-1: the IGF-1 chain with arginine in place of glutamate at position 3 and an extra 13 amino acid piece on the front end. It binds the body's IGF binding proteins only weakly. It was made as a research reagent and cell culture supplement, not as a medicine. [2]
Other names: Long R3 IGF-I, Long [Arg3]-IGF-I, LR3IGF-I, LongR3-IGF-I, LONG R3IGF-I.
How it has been given to people: no human use on record.
Looking for doses? IGF-1 LR3 dosage chart and vial math
Is IGF-1 LR3 approved in the US and Canada?
United States: Not FDA approved: Drugs@FDA holds no IGF-1 LR3 product, and the only IGF-1 products it lists are mecasermin products, which are a different molecule. [14]
Canada: No IGF-1 LR3 product is in Health Canada's Drug Product Database; the IGF-1 product it lists is Increlex (mecasermin, DIN 02509733), which is a different molecule. [15]
Both were checked on 10 Oct 2026 against the regulators' own product databases.
Which approved products contain IGF-1 LR3?
No approved medicine containing IGF-1 LR3 was found in the US or Canada. Anything sold under this name is not a regulated product, so there is no label to check a dose against.
What human studies of IGF-1 LR3 exist?
The 14 findings listed here: 14 from animal or lab work.
In rats it is cleared from the blood much faster than IGF-I, because it does not stay attached to the binding proteins. [4]
After an intramuscular injection in rats, intact LR3 was no longer detectable in blood after 4 hours, while two other IGF-I analogs were detected until 24 hours. [8]
In growing female rats, a 14-day infusion under the skin increased weight gain and nitrogen retention; 44 mcg a day of LR3 matched 278 mcg a day of IGF-I. [3]
In pigs, IGF-I variants including LR3 lowered blood sugar 2 to 3 times more strongly than IGF-I, and for much longer. [5]
The low blood sugar lasted far longer than with IGF-I. [5]
In pigs it did the opposite of what it did in rats: a 4-day infusion reduced daily weight gain and food intake and lowered the animals' own IGF-I, IGFBP-3 and insulin. [6]
The same pig study found it suppressed the animals' own growth hormone release. [6]
In guinea pigs a 7-day infusion enlarged the adrenals, gut, kidneys and spleen without increasing overall growth. [7]
The analog was first described in 1992 as one of a set of IGF-I fusion proteins made in E. coli, which the authors presented as reagents for studying how IGF-I works. [1]
In cells that release IGF binding proteins it was more potent than IGF-I, but in a cell line that releases none it was less potent than IGF-I. Its extra strength comes from escaping the binding proteins, not from a stronger action at the receptor. [1]
IGF-I binds the binding proteins about 1000 times more tightly than LR3 does. [4]
A paper from the company that supplies it for cell culture describes it as engineered for use in biopharmaceutical protein production in mammalian cells. [10]
A French anti-doping laboratory found black market IGF-I analog products to be of poor quality, with oxidised forms of the peptide. [8]
A black market injection vial analysed in Germany contained His-tagged Long R3 IGF-I, a form normally made for laboratory work; the authors judged it a by-product of biochemical studies, not something made for injection. [9]
What are the side effects of IGF-1 LR3?
No side effect data from human studies was found for IGF-1 LR3. That is a gap in the research, not a sign that it is safe.
How does IGF-1 LR3 compare with others in its group?
These are the peptides filed under growth hormone. The last column says whether a randomized human trial is on record for each.
| Peptide | US | Canada | Half-life | Randomized human trial |
|---|---|---|---|---|
| Ipamorelin | Not approved | Not authorized | Terminal half-life of about 2 hours after a 15-minute intravenous infusion in healthy men. No human figure after injection under the skin was found. | Yes |
| CJC-1295 without DAC | Not approved | Not authorized | Not found | No |
| CJC-1295 with DAC | Not approved | Not authorized | Estimated at 5.8 to 8.1 days in healthy adults after injection under the skin. | Yes |
| Sermorelin | No longer sold | Not authorized | Disappearance half-time of about 4.3 minutes after a 90-minute intravenous infusion in 10 healthy men. No human half-life after injection under the skin was found in the abstracts read. | Yes |
| Tesamorelin | Approved for one use | No longer sold | About 8 minutes in healthy adults after one 1.4 mg dose of Egrifta SV under the skin. Other labels give other figures for other formulations and conditions (see also). | Yes |
| IGF-1 LR3 | Not approved | Not authorized | Not found | No |
| GHRP-2 | Not approved | Not authorized | About 0.55 hours (33 minutes) for the slower phase after a single dose into a vein in 10 children. No human half-life after injection under the skin was found in the abstracts read. | Yes |
| GHRP-6 | Not approved | Not authorized | After a single dose into a vein in nine healthy men: distribution half-life about 7.6 minutes, elimination half-life about 2.5 hours. No human half-life after injection under the skin was found. | No |
| HGH | Approved, prescription | Authorized, prescription | About 3.8 hours after an injection under the skin in healthy subjects. The label says this long figure reflects slow absorption from the injection site. | Yes |
What could not be found
These were searched for and did not turn up. They are listed so a missing number is not mistaken for a hidden one.
- Any human study of IGF-1 LR3. A PubMed search across its name variants (Long R3, LR3 IGF, LR3IGF, LongR3, Long Arg3, IGF-1 LR3) returned 175 records; the 55 indexed under Humans were checked by title and are cell culture, assay or doping-detection papers, not dosing studies.
- Any registered trial: five ClinicalTrials.gov searches returned 0 studies [13]. A search for LR3 alone returns acupuncture trials, because LR3 is also the name of an acupuncture point.
- A 2026 peer-reviewed review ([11], full text) reaches the same result, placing IGF-1 LR3 among compounds 'for which no peer-reviewed human studies exist at all'.
- Human dose, human half-life, human side effects: none on record.
- A half-life figure in any species: the abstracts read give clearance comparisons and detection times in rats, not a half-life.
- Any approved product or label anywhere, so no official contraindications, interaction list or storage instructions.
- A Health Canada advisory or FDA compounding entry naming IGF-1 LR3.
IGF-1 LR3 questions
Is IGF-1 LR3 approved in the US?
Not FDA approved: Drugs@FDA holds no IGF-1 LR3 product, and the only IGF-1 products it lists are mecasermin products, which are a different molecule.
Is IGF-1 LR3 authorized in Canada?
No IGF-1 LR3 product is in Health Canada's Drug Product Database; the IGF-1 product it lists is Increlex (mecasermin, DIN 02509733), which is a different molecule.
Has IGF-1 LR3 been tested in a randomized human trial?
No randomized human trial was found. What exists is listed under the studies heading on this page.
Sources
Each one was opened on 10 Oct 2026 and matched to the line it supports.
- 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. PubMed 1378742.
- Laajoki LG et al. Secondary structure determination of 15N-labelled human Long-[Arg-3]-insulin-like growth factor 1 by multidimensional NMR spectroscopy. FEBS Lett 1997. PubMed 9450557.
- Tomas FM et al. Anabolic effects of insulin-like growth factor-I (IGF-I) and an IGF-I variant in normal female rats. J Endocrinol 1993. PubMed 8371075.
- Ballard FJ et al. Effects of interactions between IGFBPs and IGFs on the plasma clearance and in vivo biological activities of IGFs and IGF analogs. Growth Regul 1993. PubMed 7683526.
- 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. PubMed 9415072.
- Dunaiski V et al. Long [R3] insulin-like growth factor-I reduces growth, plasma growth hormone, IGF binding protein-3 and endogenous IGF-I concentrations in pigs. J Endocrinol 1997. PubMed 9488001.
- 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. PubMed 7561636.
- Mongongu C et al. Detection of LongR(3) -IGF-I, Des(1-3)-IGF-I, and R(3) -IGF-I using immunopurification and high resolution mass spectrometry for antidoping purposes. Drug Test Anal 2021. PubMed 33587816.
- Kohler M et al. Detection of His-tagged Long-R3-IGF-I in a black market product. Growth Horm IGF Res 2010. PubMed 20675162.
- Voorhamme D et al. LONG R3IGF-I as a more potent alternative to insulin in serum-free culture of HEK293 cells. Mol Biotechnol 2006. PubMed 17172665.
- 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. PubMed 42395176.
- INCRELEX (mecasermin) injection: US prescribing information (a different molecule, cited only for comparison) via openFDA and DailyMed 2026-05-18. api.fda.gov.
- ClinicalTrials.gov searches: IGF-1 LR3, IGF-I LR3, Long R3, LongR3, LR3 IGF (0 studies each) clinicaltrials.gov.
- Drugs@FDA lookups via openFDA: no record for LR3 or Long R3; mecasermin returns Increlex and Iplex only US Food and Drug Administration. api.fda.gov.
- Health Canada Drug Product Database: active ingredient search for mecasermin (1 record, INCRELEX); no record for IGF-1 LR3 Health Canada. health-products.canada.ca.
- The Prohibited List (2026 list as shown on the WADA website) World Anti-Doping Agency. wada-ama.org.
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