IGF-1 LR3: What It Does, Dosage Claims, Risks, Legal Status

Key takeaways

• IGF-1 LR3 ("Long R3 IGF-1") is a lab-made version of insulin-like growth factor 1, built in 1992 as a research reagent: IGF-1 with a 13-amino-acid extension and an arginine swapped in at position 3, so it escapes the proteins that normally buffer IGF-1 in blood. It is not a supplement, a steroid or an approved drug.
• No human has been studied on it. Our PubMed search found no human study of any kind, and a 2026 review places it in the lowest evidence tier. In animals it was more anabolic than IGF-1 in rats and slowed growth in pigs. Real human IGF-1, given to healthy adults, did not change muscle or fat mass.
• The doses that circulate online, 20 to 40 mcg a day in 4- to 6-week cycles, come from forums, not studies. The approved IGF-1 drug, mecasermin, is dosed by body weight, only with a meal, because it lowers blood sugar.
• The documented risks of IGF-1 excess are hypoglycemia (in 42% of children in the approved drug's trials), tissue and organ overgrowth, raised pressure inside the skull and allergic reactions. Higher natural IGF-1 is linked with modestly higher rates of some cancers; whether drug-driven IGF-1 does the same is unproven, and the approved drug is contraindicated in malignancy.
• There is no legal source: it is not approved, not in any category of FDA's May 14, 2026 compounding list, and, at 83 amino acids, a biological product that FDA places outside 503A and 503B compounding. WADA prohibits it at all times as an IGF-1 analogue.

IGF-1 LR3 at a glance

Also called

Long R3 IGF-1, LR3-IGF-I, Long Arg3 IGF-I, IGF-1 Long R3

Class

Synthetic analog of insulin-like growth factor 1 (IGF-1) made as a laboratory reagent: an 83-amino-acid protein that binds the IGF-1 receptor but escapes the binding proteins that normally buffer IGF-1 in blood

Route

None approved. Studied by infusion and injection in animals only; sold as research vials for injection

FDA status

Not approved anywhere and never tested in a published human study. The only approved IGF-1 drug is mecasermin (Increlex), a different molecule identical to human IGF-1, for growth failure in children with severe primary IGF-1 deficiency.

FDA Category 2 (compounding restricted)

No

Available by prescription (US)

No legal source: not approved, not in any category of FDA's 503A nominations list, and as a protein (a biological product) outside 503A and 503B compounding

Best-studied use

Cell culture and animal studies (rats, pigs, guinea pigs, fetal sheep); no human study of any kind

Typical monthly cost (telehealth, 2026)

No legal product exists to price; research vials are unapproved drugs and we do not list their prices

What IGF-1 LR3 is and how it works

Insulin-like growth factor 1 (IGF-1) is a 70-amino-acid hormone made mostly by the liver when growth hormone (GH) signals it to. It carries most of GH's effects on growth: it acts on the type 1 IGF receptor, a close relative of the insulin receptor, to drive cell growth and protein synthesis and to pull glucose, fatty acids and amino acids into tissues. In blood, more than 80% of it travels bound to a binding protein (IGFBP-3) and a second protein in a large complex, which keeps it in reserve and slows its clearance (Increlex label).

IGF-1 LR3 was designed in Adelaide, Australia, to get around that reserve. Researchers attached the first 11 amino acids of porcine growth hormone, plus two linker amino acids, to the front of IGF-1, and replaced the glutamic acid at position 3 with arginine; "Long" refers to the extension and "R3" to the arginine (Francis 1992). The result binds the IGF binding proteins very poorly. In cultured rat muscle cells, which secrete binding proteins, it was more potent than IGF-1, while in chicken fibroblasts, which secrete none, it was less potent, which showed that the extra potency comes from escaping the binding proteins, not from a stronger grip on the receptor. The authors described the analogues as useful reagents for studying IGF-1 action, and that is what IGF-1 LR3 became: a cell-culture and laboratory tool.

Two consequences matter for anyone reading a sales page:

1. More free hormone, cleared faster. Because it is not held by binding proteins, LR3 reaches tissues readily, but in rats it is also cleared from the blood more quickly than IGF-1 (Tomas 1996). After a single intramuscular injection in rats, the intact molecule was no longer detectable after about 4 hours (Mongongu 2021). The long human half-life quoted online has never been measured.
2. Insulin-like effects come with it. IGF-1 suppresses the liver's glucose output and increases glucose uptake, which is why the approved IGF-1 drug lowers blood sugar (Increlex label). An analog that bypasses the buffer bypasses that brake too.

Three products get confused under the same name. IGF-1 LR3 is the research analog. Mecasermin (Increlex) is recombinant human IGF-1 with a sequence identical to the natural hormone, an approved pediatric drug. "IGF-1 supplements", mostly deer antler velvet and colostrum products, are oral products whose IGF-1 content and absorption are a separate question, covered in IGF-1 supplements vs IGF-1 peptides. None of the three is an anabolic steroid: they act on a growth-factor receptor, not the androgen receptor, as our explainer are peptides steroids? sets out.

What the evidence actually shows

There is no human evidence on IGF-1 LR3. A 2026 review of performance peptides acting on the GH and IGF-1 axis found no peer-reviewed human studies and placed it, with PEG-MGF and CJC-1295 without DAC, in its lowest tier, supported only by preclinical data and user reports (Dominikowski 2026). What follows grades the claims using animal data for LR3 and human data for IGF-1 itself, which is the closest proxy that exists.

IGF-1 LR3 claims, graded by the evidence behind them

Claim	Grade	What the evidence shows	Sources
Escapes IGF binding proteins and is more potent than IGF-1	D	In cell lines that secrete binding proteins, LR3 was among the most potent analogs tested; in cells that secrete none, it was less potent than IGF-1. In rats, infused LR3 was 1.5 to 2 times as potent as IGF-1 for weight gain and organ growth.	Francis 1992; Tomas 1996
Builds muscle	D	No human study. In rats made catabolic with dexamethasone, injected LR3 was barely equipotent with IGF-1 for reversing muscle loss, although it was more potent for body weight and organ weights.	Tomas 1996
Long-acting (a half-life of a day or more)	D	The opposite in animals: LR3 is cleared from rat blood faster than IGF-1, and after a 100 mcg/kg intramuscular dose in rats the intact molecule disappeared after about 4 hours. No human pharmacokinetic data exist.	Tomas 1996; Mongongu 2021
IGF-1 itself builds muscle or burns fat in healthy adults	B	Evidence against. 56 recreational athletes given IGF-1 with its binding protein (30 or 60 mg a day) for 28 days had no change in lean or fat mass; VO2max rose about 7%. 16 women aged about 70 given IGF-1 15 mcg/kg twice daily for a year had no change in lean mass, fat, bone or strength.	Guha 2015; Friedlander 2001
Treats severe primary IGF-1 deficiency in children (mecasermin, not LR3)	A	The approved indication. In the pooled trials (71 children, mean treatment 3.9 years), height velocity rose from 2.8 cm a year before treatment to 8.0 cm in the first year.	Increlex label
Lowers blood sugar	B	Documented for IGF-1: hypoglycemia in 42% of treated children, some with seizures. In pigs, LR3 lowered glucose 2 to 3 times more potently than IGF-1 and kept it down longer.	Increlex label; Tomas 1997
Speeds recovery, causes muscle 'hyperplasia', or works locally at the injection site	D	No human study of any of these. The review that graded LR3 found only preclinical extrapolation and forum reports.	Dominikowski 2026
Anti-aging	D	No LR3 data. Restoring IGF-1 to young-adult levels for a year in older women changed none of the measured outcomes, including mood and memory, and the trial was stopped early.	Friedlander 2001

The pattern is consistent. The mechanism is real: LR3 does activate the IGF-1 receptor and does more per microgram than IGF-1 in rats. The outcome people buy it for, more muscle in a healthy adult, has never been tested with LR3, and when the real hormone was tested in healthy adults, body composition did not move. Animal results also point in different directions by species: LR3 promoted growth in rats, but a four-day infusion of 180 mcg/kg a day in finishing pigs reduced their growth and food intake and suppressed their own GH, IGF-1 and IGFBP-3 (Dunaiski 1997). Rat results do not transfer automatically, even to other mammals.

What you are promised versus what is documented

Sales pages and forums attribute the same list of effects to IGF-1 LR3: muscle growth and "hyperplasia", fat loss, faster recovery, nutrient partitioning, and a long half-life that allows one injection a day.

• Documented in humans: nothing for LR3. For IGF-1 itself: growth in children with severe IGF-1 deficiency; lower blood sugar; in healthy adults, no change in lean or fat mass over 28 days or a year.
• Documented in animals: more potent anabolic effects than IGF-1 in rats, mostly visible as weight gain and heavier visceral organs; stronger and longer glucose lowering in pigs; reduced growth and suppression of the animal's own GH and IGF-1 in pigs.
• Not supported anywhere: a 20- to 30-hour half-life, site-specific muscle growth, hyperplasia in humans, fat loss, or any anti-aging effect.

IGF-1 LR3 vs mecasermin, growth hormone and the GHRH analogs

Read the sermorelin profile and the HGH peptides guide for the prescribable side of this table, and our muscle-growth ranking for how all of these compare on evidence.

Dosage: the claims versus what was studied

Two things stand out. The forum dose is far below the weight-based IGF-1 doses used in people, but that does not make it a "low" dose of LR3, because LR3 is several times more potent per microgram than IGF-1 in animals and its potency in humans is unknown. And the approved drug, a weaker molecule by that measure, has to be given with food because of hypoglycemia. Our IGF-1 LR3 dosage page sets out the claimed and studied numbers in more detail.

We do not publish a reconstitution example for IGF-1 LR3. The reconstitution calculator is for medications a pharmacy has dispensed with a labeled concentration; a research vial has neither a legal status nor a verified content. Anti-doping chemists who analyzed black-market IGF-1 analog products found abundant oxidized, lower-quality forms of the peptides (Mongongu 2021).

Side effects and who should not use it

There are no human safety data for IGF-1 LR3. What is known comes from the approved IGF-1 drug, from adults given IGF-1 in trials, and from conditions of IGF-1 excess. Our guide to side effects of peptides in bodybuilding sets these risks beside those of the other compounds sold for muscle.

What IGF-1 excess is documented to do

• Hypoglycemia. In the mecasermin trials, 30 of 71 children (42%) had at least one episode, 5 had severe episodes needing assistance and 4 had seizures or lost consciousness. The label tells patients to avoid driving and exercise for 2 to 3 hours after a dose while the dose is being established (Increlex label). In pigs, LR3's glucose-lowering effect was stronger and longer than IGF-1's (Tomas 1997), which matters for anyone who injects after training on an empty stomach.
• Tissue and organ overgrowth. Tonsillar enlargement in 15% of treated children, with tonsillectomy in 7 and sleep apnea in 3; rapid growth in kidney and spleen length; thickening of facial soft tissues; and, with long-term overdose, signs of acromegaly (Increlex label).
• Raised pressure inside the skull (intracranial hypertension) with headache, visual changes and papilledema, in 3 of the 71 children, and allergic reactions up to anaphylaxis, estimated at about 0.3% after approval (Increlex label).
• In adults at high doses: in seven insulin-resistant adults given 120 to 160 mcg/kg twice daily, side effects forced every patient to stop: swelling of the face and hands, jaw tenderness, joint and muscle pain, fatigue, a fast heart rate, flushing and low blood pressure on standing (Jabri 1994).

The cancer question

IGF-1 is a growth and survival signal for cells, so the cancer question is unavoidable, and it is also easy to overstate. Three pieces of evidence frame it:

• Natural IGF-1 levels. In a meta-analysis of 21 studies with 3,609 cancer cases, people with IGF-1 at the 75th rather than the 25th percentile had higher odds of prostate cancer (odds ratio 1.49) and premenopausal breast cancer (1.65); the authors called the associations modest and variable between sites (Renehan 2004).
• Acromegaly, where GH and IGF-1 are both chronically high. In a Danish national cohort of 529 patients, cancer incidence was not significantly raised (standardized incidence ratio 1.1), though overall mortality was (1.3). Pooling 23 studies gave an overall cancer ratio of 1.5, with higher ratios for colorectal (2.6) and thyroid (9.2) cancer, and the authors warned that smaller single-center studies inflated the estimates (Dal 2018).
• The approved drug. Mecasermin is contraindicated in children with a malignancy or a history of one. Malignancies have been reported after approval; the label says it is unknown whether they are related to the drug, that most occurred in children with cancer-predisposing conditions, and that they were seen more often at higher than recommended doses or with IGF-1 above the normal range. In a two-year rat study it increased adrenal tumors and, at high doses, skin and mammary tumors (Increlex label).

None of this shows that IGF-1 LR3 causes cancer. It shows why every regulated IGF-1 product excludes people with cancer, and why an unmonitored analog designed to deliver more free IGF-1 activity is not something to take with a cancer history.

Who should not use it

Even setting aside that there is no legal product: anyone with an active or past cancer; anyone with diabetes or on insulin or sulfonylureas; anyone pregnant or breastfeeding; anyone under 18; anyone with a history of intracranial hypertension or sleep apnea; and anyone subject to drug testing.

Legal status in the United States

IGF-1 LR3 fails every route to a legal product. Applying the tests our legal tracker uses:

The last row decides the matter. FDA's position is that biological products subject to licensure under the Public Health Service Act are not eligible for the compounding exemptions in sections 503A and 503B (FDA 2020). On that reading, even mecasermin, an approved molecule, cannot be compounded, and IGF-1 LR3 could not become a compounded product through a nomination the way BPC-157 might: a protein needs a biologics license. As far as FDA's published list shows, no one has nominated IGF-1 LR3 for compounding at all.

That leaves the research-chemical market. Possessing a vial is not a crime, but selling it for human use is selling an unapproved drug, and FDA's 2026 warning letters to research-peptide vendors rejected "research use only" labels where websites supplied dosing guides, calculators or bacteriostatic water, as the tracker records.

In tested sport: prohibited at all times

WADA's Prohibited List names "insulin-like growth factor 1 (IGF-1, mecasermin) and its analogues" in section S2.3, growth factors and growth factor modulators. All of S2 is prohibited at all times, in and out of competition, and its substances are non-specified (WADA). IGF-1 LR3 is an IGF-1 analogue, and anti-doping laboratories have published methods that detect it and its breakdown products in blood (Mongongu 2021).

What to do instead

If the goal is more muscle, the honest ranking in our muscle-growth guide is that no injectable peptide has been shown to build muscle in healthy adults, and the compound with real muscle evidence is testosterone, prescribed for diagnosed deficiency. Adding IGF-1 LR3 to a stack does not change that, as our muscle-stack guide explains. If the goal is to raise a low IGF-1, the first step is finding out why: the mecasermin label lists GH deficiency, malnutrition, hypothyroidism and chronic corticosteroid treatment as causes of secondary IGF-1 deficiency that the drug is not meant to treat (Increlex label). A clinician can test for those. For a symptomatic adult with low IGF-1 and a working pituitary, sermorelin and tesamorelin are the prescribable GH-axis options, at the prices in our cost guide; our guide to who qualifies for peptide therapy covers the evaluation. If you are considering an oral "IGF-1" product instead, read IGF-1 supplements vs IGF-1 peptides first.

Women and older adults

There are no IGF-1 LR3 data in women. The closest evidence is the year-long IGF-1 trial in postmenopausal women aged over 60, which raised IGF-1 to young-adult levels and changed nothing measured: lean mass, fat, bone density, strength, mood or memory (Friedlander 2001). Pregnancy and breastfeeding are absolute reasons to avoid it. For older adults generally, the mecasermin label notes that safety and effectiveness after 65 have not been established (Increlex label), and the hypoglycemia risk is harder to manage alongside diabetes medications.

Bottom line

IGF-1 LR3 is a well-characterized laboratory tool and an uncharacterized drug. It does what it was designed to do in cell culture and animals, activating the IGF-1 receptor while escaping the proteins that normally restrain IGF-1, and that same design is what makes its blood-sugar effect stronger and less predictable. No one has studied it in a person, the real hormone did not change body composition in the healthy adults who received it, and the doses that circulate online come from forums. There is no legal product to buy or prescribe, and it is prohibited at all times in tested sport. The legal tracker will note any change, but as a protein without a biologics license, IGF-1 LR3 has no path to a pharmacy shelf.

Frequently asked questions

+−Is IGF-1 a peptide?

Biochemically, yes: IGF-1 is a chain of 70 amino acids, a polypeptide hormone made mainly by the liver in response to growth hormone. Legally, no: FDA defines any chain longer than 40 amino acids as a protein, which makes IGF-1 and the 83-amino-acid IGF-1 LR3 biological products rather than peptide drugs. That distinction is one reason no compounding pharmacy may make either one.

+−What does IGF-1 LR3 do?

It activates the IGF-1 receptor, the same receptor natural IGF-1 uses to drive growth, protein synthesis and glucose uptake. Because of its extra 13 amino acids and an arginine swap at position 3, it barely binds the proteins that normally hold IGF-1 in reserve in the blood, so more of it is free to act. In rats it promoted weight gain more potently than IGF-1; in pigs it slowed growth and suppressed the animals' own growth hormone and IGF-1. Nobody has measured what it does in a person.

+−Is IGF-1 LR3 a steroid?

No. Anabolic steroids are testosterone derivatives that act on androgen receptors. IGF-1 LR3 is a modified growth factor, a protein that acts on the IGF-1 receptor, which is closely related to the insulin receptor. Its main acute danger is the opposite of a steroid's: it can drop blood sugar. Both are prohibited at all times in tested sport.

+−Is IGF-1 LR3 legal in the US?

Possessing it is not a crime, but there is no legal way to buy it as a drug. It has never been approved, it is not in any category of FDA's 503A nominations list (updated May 14, 2026), it is not a component of an approved drug, and as an 83-amino-acid protein it is a biological product, which FDA says is outside the compounding exemptions altogether. Vials sold as research chemicals are unapproved drugs when they are sold for people to inject.

+−Can a doctor prescribe IGF-1?

A doctor can prescribe mecasermin (Increlex), the approved recombinant human IGF-1, which is indicated only for growth failure in children 2 and older with severe primary IGF-1 deficiency or growth hormone gene deletion with neutralizing antibodies. Prescribing it to adults for muscle or anti-aging would be off-label use of a pediatric specialty drug with serious hypoglycemia warnings. No doctor can prescribe IGF-1 LR3, because there is no product to prescribe.

+−What are the side effects of IGF-1 LR3?

No human side-effect data exist for IGF-1 LR3 itself. The approved IGF-1 drug shows what the receptor does when stimulated: hypoglycemia in 42% of treated children in its trials, sometimes severe enough to cause seizures, plus tonsil and adenoid enlargement, raised pressure inside the skull and allergic reactions. Adults given high doses of IGF-1 developed facial and hand swelling, jaw pain, joint and muscle pain, a racing heart and low blood pressure on standing. In pigs, LR3 lowered blood sugar more strongly and for longer than natural IGF-1.

+−Does IGF-1 LR3 cause cancer?

Nobody knows, because it has never been studied in people. The concern is reasonable: people whose own IGF-1 runs high have modestly higher rates of prostate and premenopausal breast cancer in pooled studies, people with acromegaly have a modestly higher cancer incidence, and the approved IGF-1 drug is contraindicated in anyone with a malignancy or a history of one. None of that proves that IGF-1 LR3 causes cancer; it is why anyone with a cancer history should not take anything that drives the IGF-1 receptor.

+−Is IGF-1 LR3 banned in sports?

Yes. WADA's Prohibited List names 'insulin-like growth factor 1 (IGF-1, mecasermin) and its analogues' under S2.3, growth factors, and the whole S2 class is prohibited at all times, in and out of competition. IGF-1 LR3 is an IGF-1 analogue, and anti-doping laboratories have published methods to detect it and its breakdown products in blood.

+−IGF-1 LR3 vs HGH: which is better?

Neither is a legal muscle builder. Growth hormone (somatropin) is an approved drug with decades of human data, but distributing it for anti-aging or bodybuilding is a federal crime, and in healthy adults its body-composition effects have not come with matching gains in strength, as our HGH guide details. IGF-1 LR3 has no human data at all. If the question is how to raise the growth hormone axis legally, the prescribable options are the GHRH analogs sermorelin and tesamorelin, with labs before and after.

Sources

1. StudyFrancis 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;8:213-23. (1992)
2. StudyTomas FM et al. Superior potency of infused IGF-I analogues which bind poorly to IGF-binding proteins is maintained when administered by injection. J Endocrinol 1996;150:77-84. (1996)
3. StudyTomas 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;155:377-86. (1997)
4. StudyDunaiski 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;155:559-65. (1997)
5. StudyMongongu 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;13:1256-69. (2021)
6. ReviewDominikowski 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 2026;17:1822475. (2026)
7. StudyGuha N et al. The effects of recombinant human insulin-like growth factor-I/insulin-like growth factor binding protein-3 administration on body composition and physical fitness in recreational athletes. J Clin Endocrinol Metab 2015;100:3126-31. (2015)
8. StudyFriedlander AL et al. One year of insulin-like growth factor I treatment does not affect bone density, body composition, or psychological measures in postmenopausal women. J Clin Endocrinol Metab 2001;86:1496-503. (2001)
9. StudyJabri N et al. Adverse effects of recombinant human insulin-like growth factor I in obese insulin-resistant type II diabetic patients. Diabetes 1994;43:369-74. (1994)
10. LabelDailyMed. Increlex (mecasermin) injection prescribing information (Eton Pharmaceuticals; SPL published May 20, 2026; label revised October 2025; BLA 021839): indication, dosage, contraindications, warnings and clinical trial adverse reactions. Read October 10, 2026. (2026)
11. ReviewRenehan AG et al. Insulin-like growth factor (IGF)-I, IGF binding protein-3, and cancer risk: systematic review and meta-regression analysis. Lancet 2004;363:1346-53. (2004)
12. StudyDal J et al. Cancer incidence in patients with acromegaly: a cohort study and meta-analysis of the literature. J Clin Endocrinol Metab 2018;103:2182-8. (2018)
13. RegulatoryFDA. Bulk drug substances nominated for use in compounding under section 503A: Category 1, 2 and 3 lists and updates (updated May 14, 2026). Read October 10, 2026. (2026)
14. RegulatoryFederal Register. Definition of the term 'biological product': final rule defining a protein as any alpha amino acid polymer with a specific, defined sequence greater than 40 amino acids in size. 85 FR 10057, February 21, 2020. (2020)
15. RegulatoryFDA. Notice to compounders: changes that affect compounding as of March 23, 2020 (biological products subject to licensure under section 351 of the PHS Act are not eligible for the exemptions in sections 503A and 503B). (2020)
16. RegulatoryWorld Anti-Doping Agency. The Prohibited List, S2 Peptide hormones, growth factors, related substances and mimetics; S2.3 Growth factors and growth factor modulators (2026 List, prohibited at all times). Read October 10, 2026. (2026)