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IGF-1 LR3: what the research shows, and what it doesn’t

By Pinnacle Pulse Editorial Team · Status as of 16 October 2026 · Next scheduled update: 14 January 2027

Short answer: IGF-1 LR3 is a modified version of the human growth factor IGF-1, designed in the early 1990s as a laboratory tool. It is not authorized as a medicine in the EU or the US. Published work on it covers cell experiments and animal studies. We found no human clinical trial in PubMed, and its safety in people is unknown.

What IGF-1 LR3 is

Start with the original. Insulin-like growth factor 1 is a hormone of 70 amino acids, made mostly in the liver when growth hormone tells it to. In the blood almost all of it travels bound to carrier proteins, the IGF-binding proteins, which control how much reaches the tissues.

IGF-1 LR3 (also written Long R3 IGF-I) is a recombinant variant with two changes. The glutamic acid at position 3 is swapped for arginine, which is where the “R3” comes from. And a short stretch borrowed from pig growth hormone is stuck onto the front, which is the “long”. Both changes make the molecule bind the carrier proteins poorly, so in a culture dish more of it stays free and active. Biochemists at the Australian research agency CSIRO in Adelaide described this family of analogues in 1992, and its main job since then has been in cell culture media.

It is worth keeping one distinction straight. Recombinant human IGF-1 with the natural sequence, called mecasermin, has been an authorized medicine in the EU since 2007, for children with severe primary IGF-1 deficiency. IGF-1 LR3 is a different molecule, and none of the clinical data on mecasermin apply to it.

What has been studied

In the dish

The 1992 paper by Geoffrey Francis and colleagues in the Journal of Molecular Endocrinology is the founding document. In rat muscle cells, the long analogues were more potent than ordinary IGF-1 at stimulating protein synthesis. The detail that explains the design comes next: in chicken cells that secrete no binding proteins, LR3 was actually less potent than IGF-1. Its advantage depends on dodging the carriers, not on hitting the receptor harder.

In rats and mice

The same Adelaide group then gave the analogues to rats. In a 1992 study in the Biochemical Journal, rats were made catabolic with the steroid dexamethasone and given IGF-1 or variants through implanted pumps. LR3 was roughly two and a half times as potent as IGF-1 at countering the weight and nitrogen loss, even though it binds the IGF-1 receptor about three times less well. The guts of treated rats also grew, by up to 45 percent in weight. That gut finding gets less attention online than the muscle numbers, though it is just as much a part of the result.

Newer animal work is scattered. A 2025 study from New York gave LR3 through the nose to male mice bred to develop Alzheimer-like plaques, for seven months. Plaque structure changed in the cortex, and body composition improved. Memory and behavior did not.

In people

We searched PubMed on 16 October 2026 for the analogue’s names combined with the publication types “clinical trial” or “randomized controlled trial”. The search returned nothing. What does involve humans is forensic. In 2010 anti-doping chemists analysed an injection vial bought on the black market and found LR3 carrying a His-tag, a handle added to proteins to make them easier to purify in the lab. Their conclusion was blunt: the effects of that material in humans “have not been elucidated or described”, and it looked more like a by-product of biochemical research than something made for injection.

A 2026 review in Frontiers in Endocrinology grouped LR3 with other peptides sold as “research compounds” and placed it at the bottom of the evidence ladder, where human studies are absent altogether.

What the research does not show

There is no human trial of IGF-1 LR3, so the research does not show any effect in people, good or bad.

It does not show safety. The approved cousin, mecasermin, is prescribed under specialist supervision for a rare condition, and EMA authorized it under exceptional circumstances because data were limited. LR3 has none of that history. Questions that matter for any growth factor, such as effects on blood sugar or on cell growth in tissues where you would not want it, have not been studied in humans.

The rat results don’t carry over in any simple way. The animals were catabolic from steroid treatment, the analogue went in through pumps, and the gut grew along with everything else.

The vial study shows the supply problem in miniature. A product sold under this name may not be what the lab papers describe.

Status as of 16 October 2026. EU and US: IGF-1 LR3 is not an authorized medicine (no entry in EMA’s medicines data or in Drugs@FDA). In the EU only mecasermin, natural-sequence IGF-1, is authorized, for severe primary IGF-1 deficiency in children. WADA: the 2027 Prohibited List names “insulin-like growth factor 1 (IGF-1, mecasermin) and its analogues” in class S2.3, prohibited at all times.

FAQ

Is IGF-1 LR3 the same as IGF-1?

No. It is a modified version with an arginine at position 3 and an extra N-terminal stretch. These changes reduce binding to IGF-binding proteins. The authorized medicine mecasermin has the natural human sequence.

Has IGF-1 LR3 been tested in humans?

Not in any clinical trial we could find in PubMed. The published studies are in cells and animals. The one human-related paper we found is a forensic analysis of a black-market vial.

Why was IGF-1 LR3 developed?

As a research reagent. Because it binds poorly to IGF-binding proteins, it stays active in cell culture, which made it useful for studying how IGF-1 works and for growing cells.

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. PMID 1378742
  • 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. PMID 1371669
  • Engel MG, 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. PMID 39610283
  • 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. PMID 20675162
  • 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. 2026;17:1822475. PMID 42395176
  • PubMed search (“long R3 IGF-I” OR “LR3 IGF-I” OR “IGF-1 LR3” OR “LR3-IGF-1” OR “Long-R3-IGF-I”) AND (clinical trial[pt] OR randomized controlled trial[pt]), run 16 October 2026 via NCBI E-utilities: 0 records.
  • EMA. Mecasermin, European public assessment report (marketing authorisation issued 2 August 2007, under exceptional circumstances). ema.europa.eu
  • WADA. 2027 Prohibited List, class S2.3. wada-ama.org
  • EMA. Download medicine data: table of all medicines assessed by EMA (Excel), checked 16 October 2026. ema.europa.eu
  • FDA. Drugs@FDA, database of FDA-approved drugs, checked 16 October 2026. accessdata.fda.gov

Facts last checked: 16 October 2026.

About this article

Written by: the Pinnacle Pulse Editorial Team, the people who make the Pinnacle Pulse app. We work only from primary sources such as regulators, legal texts, trial registries and PubMed, and we remove claims we can’t check against one.

This article has not been reviewed by a physician. It is general information, not medical advice.

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Change log

  • 16 October 2026: First published.

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