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What it is
A modified analogue of insulin-like growth factor 1, carrying an arginine substitution at position 3 and a 13-amino-acid N-terminal extension. It was developed as a bioreactor and cell-culture reagent, and that remains what it is manufactured and sold for.
How it is proposed to work
The modifications drastically reduce binding to IGF binding proteins, so more of the molecule circulates free and active at the IGF-1 receptor. The community reads this as an extended half-life. That is backwards: native IGF-1 circulates for a long time precisely because it is sequestered in a large IGFBP-3 complex, and a molecule that evades that complex is cleared faster, not slower. The one study that compares the two peptides head to head in the same animals puts LR3IGF-I's metabolic clearance about an order of magnitude above native IGF-1's, with most of it circulating as free peptide. That is rat work after an intravenous bolus, and no human measurement exists — but it points the opposite way to the claim it is used to support. What the modification buys is potency, not duration.
Approved medical uses
None. IGF-1 LR3 has no approved human medical indication in the jurisdictions we track. Any use is outside an approved label.
Human research
Each entry states what the study found and, separately, what it cannot show.
No adequate published human research. This absence is the reason for the evidence grade above — it is not a gap we can fill with animal data.
Preclinical research
Animal and laboratory work. Useful for generating hypotheses; it cannot establish that something works in people.
- Animal1996
Plasma clearance of IGF-I, des-(1-3)IGF-I and LR3IGF-I in a rat model of chronic renal failure
Finding. In a rat model of chronic renal failure, total clearance of IGF-I was not significantly altered, although its half-life and area under the curve were increased in the rapid distribution phase and reduced in the slow elimination phase; total clearance of LR3IGF-I, an analogue that binds poorly to IGF binding proteins, was significantly increased. Increased degradation of both IGF-I and LR3IGF-I was associated with reduced IGF binding in the 150-kDa complex, and separately, reduced binding of IGF-I in the 150-kDa complex and increased binding to smaller-molecular-weight IGF binding proteins were observed in renal failure. The results suggest this may explain, at least in part, the reduced bioactivity of IGF-I observed in that condition.
Limitation. Animal pharmacokinetics in a disease model: the abstract describes a rat model of chronic renal failure throughout, and the analogues were used there as a probe of IGF-binding-protein effects on clearance and degradation. The comparison run throughout is renal failure against normal animals, peptide by peptide — not LR3IGF-I against native IGF-I — so it cannot be read as measuring how fast this analogue clears relative to IGF-1. Although des-(1-3)IGF-I is named in the paper title, the abstract reports no result for it. No animal numbers are stated.
- Animal1993
Direct clearance comparison of IGF-I against LR3IGF-I in rats
Finding. Radiolabelled IGF-I and the analogue LR3IGF-I were given as intravenous boluses to catheterised virgin and pregnant rats, so the two peptides are compared against each other in the same animals. LR3IGF-I was cleared from plasma more rapidly than IGF-I: metabolic clearance rate 9.84 in virgin rats against 0.90 for IGF-I, in millilitres per minute per kilogram — roughly an order of magnitude faster. Most LR3IGF-I circulated as free peptide, whereas IGF-I in virgin rat plasma was mainly associated with the 150-kDa complex. More small-molecular-weight breakdown products appeared wherever binding-protein association was reduced, which the authors read as greater rates of IGF degradation, and more LR3IGF-I than IGF-I tracer was recovered from kidneys, ovaries and adrenals.
Limitation. Rats, and the head-to-head comparison is incidental to the paper's own question, which was whether pregnancy-related changes in binding proteins alter IGF clearance. Clearance was measured after a single intravenous bolus of radiolabelled peptide, not after subcutaneous administration of unlabelled material, and the abstract states no animal numbers. It measures how quickly the analogue leaves plasma, not what it does in tissue over time, and none of it is a human result.
Potential safety concerns
- SeriousPromising
Hypoglycaemia. IGF-1 has insulin-like activity, and a more potent free-circulating analogue makes this worse. The widely repeated half-life figures have no primary support, and people who believe them dose accordingly — which is a plausible mechanism for an acute event.
- SeriousEstablished
It is an unlicensed biologic sold as a laboratory reagent. Suppliers explicitly prohibit human use, so there is no pharmaceutical-grade supply chain, no sterility assurance for injection, and no manufacturer accountability of any kind.
- CautionPreliminary
Epidemiological studies associate higher circulating IGF-1 with cancer risk for several tumour types. These are observational associations at physiological ranges, not evidence that this analogue causes cancer — but they are the reason sustained supraphysiological IGF-1 signalling would need proper study before anyone offers reassurance.
- CautionEstablished
Prohibited in sport.
Known interactions and contraindication considerations
- Additive hypoglycaemia risk with insulin and insulin secretagogues.
- Not otherwise characterised in humans, because it has not been studied in humans.
This list is not exhaustive and is not a substitute for a clinician reviewing your full medication history.
Regulatory status
Status is shown per jurisdiction and is accurate only as of the date stated. Where a compound is approved, the approval is bound to a specific formulation, manufacturer and indication — shown in the detail column.
| Jurisdiction | Standing | Detail |
|---|---|---|
United States FDA | Unapproved / investigational as of 6 Aug 2026 | Not approved and not a medicine. Mecasermin (recombinant human IGF-1) is a separate, approved product for severe primary IGF-1 deficiency — that approval says nothing about this analogue. |
European Union EMA | Unapproved / investigational as of 6 Aug 2026 | No marketing authorisation. |
India CDSCO | Unapproved / investigational as of 6 Aug 2026 | Not approved for human use. Would fall under the new-drug pathway. |
How it is being used
What the grey community actually runs, the reasoning they give, and our read on whether it follows from known biology. This is observation, not evidence, and not a recommendation.
No community use documented for this compound yet. Absence here means our editorial team has not reviewed and verified a pattern — not that none exists.
Active clinical trials
No registered trials currently tracked for IGF-1 LR3.
What remains unknown
The questions that would change our assessment if they were answered.
- What is the actual human half-life? The circulating figures appear to have no primary source.
- Does evading binding proteins change the tissue distribution in ways that matter?
- What would sustained supraphysiological IGF-1 receptor signalling do over years?
References
- 1.Gillespie CM, Hazel SJ, Walton PE, et al. Effects of chronic renal failure on plasma clearance of insulin-like growth factor I, des-(1-3)IGF-I, and LR3IGF-I. Am J Physiol. 1996.PMID 8897852doi
- 2.Bastian SE, Walton PE, Wallace JC, Ballard FJ. Plasma clearance and tissue distribution of labelled insulin-like growth factor-I (IGF-I) and an analogue LR3IGF-I in pregnant rats. J Endocrinol. 1993.PMID 7693845doi
Editorial change history
When we change a grade or a regulatory note, we log it here rather than editing quietly.
Dossier created. Fact-check correction applied before publication: the extended-half-life premise repeated across vendor listings is backwards, and there is no boxed warning on the Increlex label — hypoglycaemia sits in Warnings and Precautions. Neither error was published.
Grade of safety-concern confirmed rather than changed, and the clearance claim behind it properly sourced. That grade never rested on the clearance figure — it rests on there being no human trial of this analogue at all, on reagent-grade supply whose own vendors prohibit human use, and on a mechanism that plausibly worsens acute hypoglycaemia risk. But proposedMechanism asserted roughly an order of magnitude higher metabolic clearance, and the only paper cited here could not support it: Gillespie 1996 compares renal failure against normal animals peptide by peptide, never LR3IGF-I against native IGF-1. The comparison that does exist is Bastian 1993, which gives both peptides to the same rats and reports metabolic clearance about eleven times higher for the analogue. Added as its own entry. The claim was right and the citation was wrong, which is the harder version of this problem to catch.
Spotted something wrong? Tell us — we publish corrections.