IGF-1 LR3: Benefits, Dosage, Side Effects and Legal Status

IGF-1 LR3 is a lab-engineered version of IGF-1, built to study how IGF-1 signalling works. It is not a hormone your body makes or a drug the FDA has approved, and it is sold today as a research chemical for muscle growth. In animals it does what its design predicts: rats gained weight and kept more nitrogen on a fraction of the dose native IGF-1 needed. It has not been tested in a controlled trial in people.

Dosing: why there is no established dose.

What is IGF-1 LR3?

IGF-1 LR3 stands for long-R3-insulin-like growth factor 1. It starts from native human IGF-1, a 70-amino-acid growth factor the liver makes in response to growth hormone. Two changes define it:

• R3: the third amino acid, glutamic acid, is replaced with arginine.
• Long: a 13-amino-acid extension is added to the front of the B-domain, for 83 amino acids in total.

Both changes are reported to sharply reduce binding to IGF-binding proteins (IGFBPs). These carrier proteins normally hold most circulating IGF-1 in reserve and control how much is free to act. A version they can’t mop up is a more potent tool for probing the IGF-1 receptor in cell culture. That is where IGF-1 LR3 comes from: a lab reagent, not a molecule developed as a medicine.

IGF-1 LR3 structure

Length

83 amino acids

Modifications

Human IGF-1 (70 residues) with Glu3 replaced by Arg and a 13-residue N-terminal extension.

No PubChem compound record. The UniProt link is for natural IGF-1, from which LR3 is engineered.

Sequence checked against FEBS Letters (1997), via PubMed.

Not mecasermin: two different molecules

The only IGF-1 product the FDA has approved is mecasermin (Increlex), which is unmodified recombinant human IGF-1. Its DailyMed label says it is indicated “for the treatment of growth failure in pediatric patients 2 years of age and older with severe primary IGF-1 deficiency or with growth hormone (GH) gene deletion who have developed neutralizing antibodies to GH.” It comes as a 10 mg/mL injection under the skin, prescribed and monitored by a doctor.

IGF-1 LR3 has a different amino-acid sequence, engineered to behave differently in the body. It has no FDA approval, no DailyMed listing and no indication. Evidence, dosing and safety data for mecasermin don’t transfer to it. A seller who invokes Increlex, or “IGF-1” in general, to suggest IGF-1 LR3 is tested or approved is overstating the record.

IGF-1 LR3 benefits: what the research shows

IGF-1 LR3 was first described in 1992 as a lab reagent for studying the IGF-1 receptor without binding proteins in the way Francis 1992 - Francis GL, Ross M, Ballard FJ 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., in the references below. The animal work that followed:

• Rats made catabolic with a steroid (dexamethasone). Given by mini-pump for 7 days, IGF-1 LR3 was about 2.5-fold more potent than native IGF-1 at reversing weight loss and improving nitrogen retention Tomas 1992 - Tomas FM, Knowles SE, Owens PC 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)(Pt 1):91-7., in the references below.
• Normal growing female rats. Over 14 days by mini-pump, 44 micrograms a day of IGF-1 LR3 matched the gains in body weight, nitrogen retention and feed efficiency from 278 micrograms a day of native IGF-1 Tomas 1993 - Tomas FM, Knowles SE, Chandler CS et al. Anabolic effects of insulin-like growth factor-I (IGF-I) and an IGF-I variant in normal female rats. J Endocrinol. 1993;137(3):413-21., in the references below.
• Diabetic rats. It was 2.5-3 times more potent than native IGF-1 at restoring growth, but did not reduce glucose loss in the urine Tomas 1993 - Tomas FM, Knowles SE, Owens PC 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)(Pt 3):781-6., in the references below.
• Gut growth in rats. In steroid-treated rats, it was severalfold more potent than native IGF-1 at enlarging the gut Read 1992 - Read LC, Tomas FM, Howarth GS et al. Insulin-like growth factor-I and its N-terminal modified analogues induce marked gut growth in dexamethasone-treated rats. J Endocrinol. 1992;133(3):421-31., in the references below.
• Pigs. A single injection lowered blood glucose 2-3 times more potently than native IGF-1, and for longer Tomas 1997 - Tomas FM, Walton PE, Dunshea FR 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., in the references below; see side effects below.
• Mice. In a mouse model of Alzheimer’s disease, 7 months of nasal IGF-1 LR3 improved body composition but did not preserve memory or behaviour Engel 2025 - Engel MG, Narayan S, Cui MH et al. Intranasal long R3 insulin-like growth factor-1 treatment promotes amyloid plaque remodeling in cerebral cortex but fails to preserve cognitive function in male 5XFAD mice. J Alzheimers Dis. 2025;103(1):113-126., in the references below.
• Fetal sheep. A one-week intravenous infusion into growth-restricted fetal sheep did not improve fetal growth White 2025 - White A, Stremming J, Wesolowski SR 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-E125., in the references below; the dosing page has its figures.

The rat results are consistent: in every rat model, IGF-1 LR3 beat native IGF-1 at promoting growth. None of these studies tests what happens when a person injects it under the skin for weeks. I found no study in people, and none registered with a trial ID I could verify.

Pharmacokinetics

I could not verify a human half-life for IGF-1 LR3, so this page doesn’t give one. Online sources often say its low binding-protein affinity makes it last longer than native IGF-1. I couldn’t trace any human half-life figure to a study I could check.

The one direct measurement of the intact molecule in blood doesn’t support the “longer-lasting” claim, though it had no native IGF-1 for comparison. After one injection into muscle in rats, unchanged IGF-1 LR3 disappeared from the blood after about 4 hours, leaving breakdown fragments. IGF-1 DES (des(1-3)IGF-1) was still detectable unchanged at 24 hours Mongongu 2021 - Mongongu C, Coudoré F, Domergue V 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;13(7):1256-1269., in the references below.

Its blood-sugar-lowering effect in pigs did outlast native IGF-1’s over a 4-hour window Tomas 1997 - Tomas FM, Walton PE, Dunshea FR 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., in the references below. Neither finding is a human half-life, so any dosing interval built on “lasts longer” has no evidence behind it.

IGF-1 LR3 dosage

With no controlled human trial and no approved product, there is no established human dose. The protocol most often used is 20-50 mcg injected under the skin once a day, usually in the morning with food, for about 1.5-6 weeks, then a 4-6 week break. Dosing guides describe this as common practice; no trial set it.

The animal studies used mini-pump infusions and single injections in rats, single injections in pigs, nasal dosing in mice and intravenous infusion in fetal sheep. None of those methods or doses translates to a person. Full detail: IGF-1 LR3 dosage.

IGF-1 LR3 side effects

There is no long-term human safety data for IGF-1 LR3. This section draws on animal findings and on the label of a related but different approved drug, marked as such.

• Low blood sugar (hypoglycaemia), measured in pigs, not people. One injection lowered blood glucose 2-3 times more potently than native IGF-1. The IGF-1 variants that bind poorly to binding proteins kept glucose down much longer, with roughly 4- to 8-fold more total hypoglycaemia over 4 hours Tomas 1997 - Tomas FM, Walton PE, Dunshea FR 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., in the references below. Mecasermin’s DailyMed label warns that “severe hypoglycemia leading to hypoglycemic seizures has been observed with INCRELEX treatment” (the label’s US spelling). Both drugs act on the IGF-1 receptor, which works alongside insulin signalling, so the two findings point the same way. No trial has measured blood glucose in a person given IGF-1 LR3.
• Abnormal tissue growth: an open question. IGF-1 signalling drives cell growth and division. No study has tested whether unsupervised IGF-1 LR3 use raises that risk either way.
• Unverified product. It is sold as a research chemical labelled not for human use. No regulator checks that a vial matches its label, and I found no public testing programme that checks identity, purity or concentration.

For redness, itching or swelling at the injection site, see injection-site reactions.

Is IGF-1 LR3 legal, and is it banned in sport?

In sport, IGF-1 and its analogues fall under the World Anti-Doping Agency’s category S2 (peptide hormones, growth factors and related substances), banned at all times. IGF-1 LR3 is an IGF-1 analogue by design and is reported to be treated accordingly. If you are a tested athlete, check the current WADA Prohibited List at wada-ama.org yourself.

I checked only US federal law, not US states or other countries.

Related reading

IGF-1 LR3 is one of several research peptides sold for muscle and recovery with no controlled human trial for that use.

• IGF-1 DES: the truncated IGF-1 analogue
• Hexarelin and other growth-hormone-releasing peptides work upstream. They prompt the pituitary to release growth hormone, which raises the body’s own IGF-1. IGF-1 LR3 is sold as a substitute for that whole chain.

Regulatory changes for this compound and others, as they happen: US peptide regulation tracker.

How IGF-1 LR3 compares

Growth hormone and growth factors. Doses for unapproved compounds are common practice, not trial-established. All growth hormone and muscle peptides →

Compound	Main use	Evidence	Usual dose	US status
HGH 191AA	Marketed to consumers for body recomposition, recovery and anti-aging in adults who do not have a diagnosed growth hormone deficiency. The identical molecule, somatropin, is FDA-approved by prescription for defined deficiency and wasting conditions - see the "Where approved somatropin fits" section on the main guide for that distinction.	Limited human data	333-1333 mcg, Once daily (split into a morning and evening dose above roughly 3 IU/day), subcutaneous	Research use only
IGF-1 LR3	Originally engineered as a laboratory reagent - an IGF-1 variant with reduced binding to IGF-binding proteins, used to study IGF-1 signalling in cell culture. Sold to consumers as a research chemical for muscle growth, a use with no controlled human trial behind it.	Animal / lab only	20-50 mcg, once daily	Research use only
IGF-1 DES	Originally isolated and studied as a naturally occurring IGF-1 fragment in laboratory pharmacology, used to probe IGF-1 receptor signalling with reduced interference from binding proteins. Sold to consumers as a research chemical for localised, site-specific muscle growth, a use with no controlled human trial behind it.	Animal / lab only	20-120 mcg, on training days only, about 4-5 times a week, not on rest days	Research use only
MGF	Marketed to consumers as a peptide injected directly into a trained muscle immediately after exercise, for local muscle repair and growth. No completed human trial has tested it for this or any outcome.	Animal / lab only	100-400 mcg, Immediately post-workout, 2-3 times a week (training days only)	Research use only
PEG-MGF	Marketed to consumers for muscle repair and growth after resistance training. Never approved for human use; FDA states it has identified no human exposure data on it by any route.	Animal / lab only	200-400 mcg, 2-3 times a week, post-workout	Research use only
Follistatin	The body's own brake on activin and myostatin signalling, studied academically as a gene-therapy payload for muscle-wasting disease. Sold separately, as an injected research-chemical protein, for grey-market muscle-building use that its own human trials have never tested.	Animal / lab only	100-500 mcg, 2 to 4 times a week	Research use only

Where to buy IGF-1 LR3 for research

Each vendor is checked against my vendor checklist.

1. 1.Next Level PharmFeatured

   1 mg vial

   • No FDA warning letter found
   • Names its testing lab
   • Batch COAs published
   • Takes card payment

   $43.99as of 3 October 2026

   View product →My Next Level Pharm review

2. 2.BioEdge Research Labs

   1 mg vial

   • No FDA warning letter found
   • Names its testing lab
   • Batch COAs published

   $67.00as of 3 October 2026

   View product →My BioEdge Research Labs review

Compare every checked vendor for IGF-1 LR3 →

See all vendors and how they compare →

Common questions

Is IGF-1 LR3 the same as mecasermin (Increlex)?

No. Mecasermin is unmodified recombinant human IGF-1, the only IGF-1 product the FDA has approved, for growth failure in children with severe primary IGF-1 deficiency. IGF-1 LR3 has a different sequence, engineered to behave differently in the body. Evidence about one does not transfer to the other.

Does IGF-1 LR3 work for muscle growth?

I could not find a controlled human trial testing it for muscle gain, body composition or performance. What is published is lab pharmacology plus a handful of animal studies: growth and nitrogen balance in rats, blood glucose in pigs, a nasal-spray study in mice and an infusion into fetal sheep. None tests what happens when a person injects it repeatedly.

Is IGF-1 LR3 legal in the United States?

It is not FDA-approved for anything, and no IGF-1 LR3 product is listed on DailyMed. It is sold as a research chemical labelled not for human use. That is a label, not a legal category.

Is IGF-1 LR3 banned in sport?

Yes. IGF-1 and its analogues fall under the World Anti-Doping Agency's S2 category (peptide hormones, growth factors and related substances), banned at all times. IGF-1 LR3 is reported as an IGF-1 analogue and treated accordingly. Tested athletes should check the current WADA list directly.

What are the side effects of IGF-1 LR3?

There is no long-term human safety data, only lab and animal studies. The main concern is low blood sugar: in pigs, one injection lowered glucose 2-3 times more potently than native IGF-1, and for longer. The label of mecasermin, a related approved drug, warns of severe hypoglycaemia including seizures. Whether it raises the risk of abnormal tissue growth is unstudied, and product purity is unverified.

Can IGF-1 LR3 cause hypoglycaemia?

It has been shown in animals, not measured in people. In pigs, one injection lowered blood glucose 2-3 times more potently than native IGF-1, and the effect lasted much longer. Mecasermin, the approved IGF-1 drug acting on the same receptor, carries a label warning of severe hypoglycaemia including seizures.

Is IGF-1 LR3 better than HGH?

No study has compared them. Somatropin (recombinant growth hormone, sold as Genotropin among others) is FDA-approved for specific growth-hormone deficiencies, with labels on DailyMed; IGF-1 LR3 is not approved for anything. Growth hormone works upstream, prompting the liver to make IGF-1, and IGF-1 LR3 is sold as a substitute for that signal. Neither has a controlled trial supporting use for muscle growth in healthy adults.

Does IGF-1 LR3 increase testosterone?

No human study has measured this, and I found no trial testing it in bodybuilders or anyone else. IGF-1 LR3 acts on the IGF-1 receptor pathway, while testosterone is controlled separately by the testes or ovaries and the pituitary. Claims that it raises testosterone have no published human support.

Is IGF-1 safe for bodybuilding?

Nobody knows, because the study that would answer it hasn't been run. There is no long-term human safety data for IGF-1 LR3, the form usually sold for bodybuilding. The clearest signal is low blood sugar: in pigs it lowered glucose more and for longer than native IGF-1, and the approved IGF-1 drug mecasermin carries a severe-hypoglycaemia warning. Products are unregulated, so content and purity are unchecked.

What is the strongest peptide to build muscle?

There is no verified answer. No controlled human trial has compared unapproved research peptides for muscle building, so "strongest" claims come from marketing. IGF-1 LR3 has no controlled human trial for muscle gain, so it can't be ranked against other compounds on evidence.

What is the usual IGF-1 LR3 dose?

No trial has tested a human dose. The protocol most often used is 20-50 mcg injected under the skin once a day, usually in the morning with food, for about 1.5-6 weeks, then a 4-6 week break. That is common practice from dosing guides, not a tested dose.

References (12 sources)

Show

Bibliographic detail is fetched from PubMed, not written by me - so a citation here cannot drift from the paper it names. Study design comes from PubMed's own tags rather than my judgement.

1. 1.Francis GL, Ross M, Ballard FJ 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.StudyPMID 1378742
2. 2.Tomas FM, Knowles SE, Owens PC 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)(Pt 1):91-7.StudyPMID 1371669full text
3. 3.Tomas FM, Knowles SE, Chandler CS et al. Anabolic effects of insulin-like growth factor-I (IGF-I) and an IGF-I variant in normal female rats. J Endocrinol. 1993;137(3):413-21.StudyPMID 8371075
4. 4.Tomas FM, Knowles SE, Owens PC 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)(Pt 3):781-6.StudyPMID 7683875full text
5. 5.Read LC, Tomas FM, Howarth GS et al. Insulin-like growth factor-I and its N-terminal modified analogues induce marked gut growth in dexamethasone-treated rats. J Endocrinol. 1992;133(3):421-31.StudyPMID 1613443
6. 6.Tomas FM, Walton PE, Dunshea FR 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.StudyPMID 9415072
7. 7.Mongongu C, Coudoré F, Domergue V 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;13(7):1256-1269.StudyPMID 33587816
8. 8.Engel MG, Narayan S, Cui MH et al. Intranasal long R3 insulin-like growth factor-1 treatment promotes amyloid plaque remodeling in cerebral cortex but fails to preserve cognitive function in male 5XFAD mice. J Alzheimers Dis. 2025;103(1):113-126.StudyPMID 39610283full text
9. 9.White A, Stremming J, Wesolowski SR 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-E125.StudyPMID 39679943full text
10. 10.INCRELEX (mecasermin) injection label - Indications and Usage, and Section 5.1 Hypoglycaemia warning- US National Library of Medicine, DailyMedlabel
11. 11.DailyMed search for "IGF-1 LR3" - zero drug package labels found (queried 24 September 2026)- US National Library of Medicine, DailyMeddatabase
12. 12.DailyMed search for "somatropin" - lists FDA-approved recombinant growth hormone labels, e.g. GENOTROPIN (queried 24 September 2026)- US National Library of Medicine, DailyMeddatabase

Keep reading

Related guides

All guides →

• bpc-157BPC-157: Benefits, Dosage, Side Effects and the ResearchWhat the BPC-157 research actually shows: benefits claims checked against a rodent literature, human dosing, side effects, and legal status.12 min readRead guide→
• 5-amino-1mq dosage5-Amino-1MQ Dosage: Common Protocol and Mouse Study DataThe 50-150 mg oral common-practice protocol for 5-Amino-1MQ, plus the one published mouse study dose - no human trial exists.4 min readRead guide→
• 5-amino-1mq5-Amino-1MQ: Capsules, Dosage, Side Effects and Legal Status5-Amino-1MQ capsules: what oral dosing was tested (in rats, not people), the 50-150 mg common protocol, mouse safety data and FDA's warning letter.5 min readRead guide→
• abaloparatideAbaloparatide (Tymlos): Uses, Dosage and Side EffectsAbaloparatide (Tymlos): the FDA-approved osteoporosis peptide - label dosing, the ACTIVE trial results, and its osteosarcoma warning.2 min readRead guide→
• abaloparatide dosageAbaloparatide Dosage: The FDA Label ScheduleAbaloparatide dosage exactly as the FDA label states it: 80 mcg once daily, the 2-year duration limit, and who should not use it.2 min readRead guide→
• adamax dosageAdamax Dosage: Why No Dose Can Be StatedAdamax dosage: only one vendor gives any figures, with no second source to check them against, and sellers disagree on what molecule is even being dosed.2 min readRead guide→