IGF-1 LR3 animal studies in rats, pigs, calves and cells, and where they stop

What is IGF-1 LR3? IGF-1 LR3, also written as long R3 IGF-I or LR3-IGF-1, is a laboratory-made analogue of insulin-like growth factor 1. It has been used in cell-culture experiments and in animal studies, as the papers below show. The animal results differ sharply by species: growth was restored in diabetic rats but reduced in pigs, and no human clinical trials of IGF-1 LR3 were found in the records reviewed. Free Muscle, which publishes this article, lists IGF-1 LR3, 60 capsules as a research compound for laboratory use only. This article summarises what the peer-reviewed IGF-1 LR3 animal studies and cell experiments report, including the measured results and the adverse findings, where the evidence stops, and why results from cells and animals cannot be carried over to people.

Key takeaways

• No human clinical trials of IGF-1 LR3 were found in the records reviewed for this article. The 2026 narrative review of GH-IGF-1 axis research-compound peptides sorts them into evidence tiers running from randomised-trial data to a complete absence of human studies, and names IGF-1 LR3 among the analogues it covers; its abstract does not say which tier LR3 sits in (Dominikowski et al., 2026).
• The published work on the analogue is from cell culture and animals, and the animal results differ sharply by species: growth was restored in diabetic rats, but reduced in pigs.
• LR3 was designed to bind IGF-binding proteins far more weakly than natural IGF-I, by at least three orders of magnitude in one embryo-culture study (Prelle et al., 2001).
• In tumour-bearing rats, the analogue increased tumour growth more than natural IGF-I did (Tomas et al., 1994).
• Route matters in the animal literature: in neonatal calves, injected LR3 changed glucose and insulin while fed LR3 did not (Hammon and Blum, 1998), and LR3 is broken down by pepsin in the laboratory (Bryant et al., 1996).
• The human clinical data found concern mecasermin (recombinant human IGF-1) or a related IGF-1 product given by injection or infusion, which are different molecules, and cannot be read as data on LR3.
• For the reported adverse findings and how the analogue differs from MK-677 and human growth hormone, see the side-effects section and the comparison section; no head-to-head trial of the three was found.
• Free Muscle sells research compounds for laboratory research use only, to customers aged 18 or over. This article is not medical advice.

What is IGF-1 LR3?

Insulin-like growth factor 1 (IGF-1, sometimes written IGF-I) is a protein hormone whose synthesis in the liver is stimulated by growth hormone (Rosenbloom, 2009).

IGF-1 LR3 is a modified version of that molecule. Its name tells you what was changed. "R3" refers to arginine at position 3, and "L" refers to a long N-terminal extension, so the full description in one animal paper is an analogue "with arginine at residue 3 and an N-terminal extension" (Tomas et al., 1993). Another paper describes long arginine 3 IGF-I as an analogue with high receptor affinity and low binding-protein affinity (Staley et al., 1998).

That second property is the point of the design. Binding proteins modulate IGF effects (Prelle et al., 2001); an analogue with low binding-protein affinity can therefore behave differently in an experiment.

It is worth separating three things that are often confused online:

• Licensed IGF-1. Mecasermin, recombinant human IGF-1, is an authorised injectable medicine in the EU for a narrow group of patients. The European Medicines Agency describes Increlex as a prescription-only solution for injection used for severe primary IGF-1 deficiency in people aged 2 to 18 years (EMA, Increlex EPAR). IGF-1 LR3 is not that authorised product.
• The laboratory analogue. IGF-1 LR3 as a research reagent, studied in vitro and in animals.
• Marketing claims. Statements made on internet pages about physique or performance. These are not evidence.

How researchers think it works

The IGF system has three parts: the ligands (IGF-I and IGF-II), the six binding proteins (IGFBP-1 to IGFBP-6), and the type 1 IGF receptor, which carries most of the biological signal (Prelle et al., 2001).

The working idea behind LR3 follows from that structure. If the analogue binds the receptor but is poorly captured by binding proteins, then in some systems it would act more potently than natural IGF-I. That held true in some experiments. In streptozotocin-induced diabetic rats, two binding-protein-resistant variants, including LR3, were reported to be 2.5 to 3 times more potent than natural IGF-I at restoring growth (Tomas et al., 1993).

The idea is not universally supported, though. In turkey satellite cells and embryonic myoblasts grown in serum-free medium, a chicken version of LR3 was significantly less active than chicken IGF-I and competed less effectively for receptor binding. The authors concluded that changing the molecule to avoid binding proteins may also change receptor affinity (Pesall et al., 2001). In other words, the design trade-off cuts both ways, and the outcome depends on the cell type and species.

A further complication is that infusing an IGF analogue can alter the body's own IGF system. Several of the animal studies below found that circulating natural IGF-I fell during LR3 infusion. The net effect on a whole animal therefore cannot be assumed from receptor-level findings alone.

Key studies at a glance

The evidence, study by study

There are no human clinical trials of IGF-1 LR3 in the records reviewed for this article, so the IGF-1 LR3 animal studies below are the core of the evidence. Everything below that concerns LR3 itself comes from cells, embryos or animals. Human trials that are mentioned later concern mecasermin or related IGF-1 products and are included only to explain what is known about IGF-1 signalling in general, not to describe LR3. Doses and infusion schedules are deliberately omitted; each paper states its own protocol in the full text linked from its PubMed record.

Diabetic rats: restoration of growth (Tomas et al., 1993)

Tomas and colleagues compared IGF-I, des(1-3)IGF-I and LR3-IGF-I in streptozotocin-induced diabetic rats of 160 g, delivering the peptides through mini-osmotic pumps. Reference groups received vehicle or insulin. Growth rate and nitrogen balance rose in a dose-dependent way. At the highest IGF-I dose, body weight rose by 48.1 g over seven days, compared with 11.0 g in the vehicle group. The two variants were 2.5 to 3 times more potent than IGF-I. All peptides raised muscle protein-synthesis rates and RNA levels by up to 50%.

The limitations are as important as the numbers. The IGFs did not reduce glucose loss in urine, whereas insulin did, and insulin-treated animals gained more weight, though that extra gain was fat rather than protein. The authors concluded that IGF-I and its variants restored growth but not other insulin-dependent processes in liver, muscle and fat. This was a diabetic model, not a healthy animal.

Tumour-bearing rats: a safety signal (Tomas et al., 1994)

In a second study, Tomas and colleagues infused IGF-I and LR3-IGF-I into rats bearing a mammary adenocarcinoma. Food intake, insulin and glucose fell, and the host did not gain muscle protein. Tumour growth was increased by the IGFs, especially by LR3-IGF-I, even though the peptides did not stimulate the tumour cells in culture. LR3-IGF-I decreased carcass fat by 30% and had no positive effect on carcass protein. Muscle protein synthesis fell and breakdown rose, though each of these tracked closely with final tumour burden.

This is a single animal tumour model, and the authors raised the possibility that some effects arose indirectly through food intake. Among the studies reviewed here, it is the clearest tumour-related animal finding: tumour growth rose with both peptides and most with LR3-IGF-I, although the abstract does not attribute this to binding-protein affinity. The 2026 review lists "biologically plausible but unproven mitogenic concerns" for peptides of this class (Dominikowski et al., 2026).

Guinea pigs: organs grew, the animal did not (Conlon et al., 1995)

In a seven-day study, female guinea pigs of 350 g were continuously infused with guinea pig IGF-I, IGF-II or LR3IGF-I. Body weight gain, feed intake, feed conversion and carcass composition were not significantly affected by any treatment. The fractional weights of adrenals, gut, kidneys and spleen were significantly increased by LR3IGF-I, but overall growth was not stimulated. Plasma IGF-I, IGF-II and IGF-binding protein concentrations were reduced (Conlon et al., 1995). For the lack of effect of IGF-I infusion on growth, the authors suggested a possible explanation: total circulating IGF concentrations were not increased by these treatments.

Finisher pigs: the opposite result (Dunaiski et al., 1997)

In a four-day study in finisher pigs, infused LR3IGF-I decreased average daily gain, food intake, and plasma IGFBP-3, IGF-I and insulin. Mean plasma growth hormone fell by 23%, and the area under the growth hormone peaks fell by 60%. The authors noted that analogues which stimulate growth in the rat inhibit it in the pig, and they suggested that suppressed growth hormone may explain the fall in IGF-I, IGFBP-3 and insulin (Dunaiski et al., 1997). Co-administration of porcine growth hormone had no interactive effect on growth performance.

Put the rat, guinea pig and pig papers side by side and the central lesson emerges: the same analogue produced growth in one species, organ-specific changes without overall growth in another, and growth inhibition in a third. Differences of this size are one reason animal findings cannot be assumed to apply to humans.

Beef heifers: protein, amino acids and glucose (Hill et al., 1999)

In an eight-hour study, beef heifers losing weight on restricted feeding received intravenous Long(R3)-IGF-1. Whole-body and skeletal muscle protein tended to be conserved, but the plasma concentrations of all amino acids measured, and of glucose, were markedly reduced. Endogenous plasma IGF-1 fell sharply in treated animals, and plasma IGF-2 fell by about 140 ng/ml in the treated group against about 40 ng/ml in controls (Hill et al., 1999). The study was brief and the protein finding was described only as a tendency.

Embryos and muscle cells: binding proteins in culture (Prelle et al., 2001; Pesall et al., 2001)

Prelle and colleagues cultured in vitro produced bovine embryos with recombinant human IGF-I, LR3, or neither. By competition assays and Western ligand blots, LR3 had an affinity for IGFBPs at least three orders of magnitude lower than IGF-I. LR3 was most efficient at stimulating early cleavage, while later development was supported most strongly by IGF-I. Blastocyst total cell counts were 105 (LR3), 96 (IGF-I) and 91 (control), with the difference mainly in trophectoderm cells (P < 0.05). Embryonic IGFBP-2 mRNA was 1.7-fold higher with LR3 than with IGF-I and 2.8-fold higher than in controls. IGF-I receptor mRNA was reduced by IGF-I but increased 1.3-fold by LR3. The authors concluded that an IGF peptide's binding-protein affinity matters for its effects on early embryos. This was an in vitro bovine embryo culture system and cannot be read as a whole-animal result.

In the turkey muscle-cell work described earlier, the opposite pattern appeared: the avian LR3 analogue was less active than the natural peptide (Pesall et al., 2001). Taken together, the two papers show that LR3 does not simply act as a stronger version of IGF-I in every cell type.

Neonatal calves: injected versus fed (Hammon and Blum, 1998)

In a seven-day study in neonatal calves, LR3 was either fed with colostrum or milk replacer or injected under the skin. Fed LR3 had no effects, whereas injected LR3 lowered plasma glucose and insulin (p < 0.05). Other measures, including lactic acid, non-esterified fatty acids, glucagon, cortisol and thyroid hormones, were not significantly affected. The authors concluded that parenteral, but not oral, LR3 affected glucose and insulin (Hammon and Blum, 1998). Among the studies reviewed here, this is the only direct comparison of fed and injected LR3.

Digestion in the laboratory (Bryant et al., 1996)

Bryant and colleagues measured how purified porcine pepsin breaks down long-R3-IGF-I. Pepsin first cut the Leu10-Phe11 bond, then several further bonds in rapid succession. They designed five single-point muteins to resist this, and one, Phe16Ala, showed a marked improvement in stability. The authors considered that mutein to have potential for oral applications to enhance gastric growth and repair. In this test-tube work, unmodified long-R3-IGF-I was cleaved by purified porcine pepsin, and the authors engineered muteins to resist that digestion.

Local gut effects in newborn pups and in rats (Staley et al., 1998; Garnaut et al., 2002)

In newborn rat pups reared artificially, Staley and colleagues found that pups fed long R3 IGF-I, like mother-fed pups, had greater villus height and cell counts than pups fed a milk replacer alone, with the LR3-fed pups showing the greatest increase. This was an artificially reared newborn rat model and does not show what happens in other settings.

In rats given LR3 by subcutaneous mini-pump, Garnaut and colleagues reported that LR3, but not natural IGF-I, increased uptake of a glucose analogue per centimetre of jejunum by up to 69%, and increased the initial rate of its appearance in plasma by 40% at the lower glucose-analogue load given by gavage. The effect was presumably due to increased mucosal mass, and significance was lost when expressed per unit of tissue weight.

Intranasal LR3 in Alzheimer's model mice (Engel et al., 2025)

A 2025 LR3-specific animal paper tested intranasal LR3-IGF-1 for seven months in male 5XFAD mice and wild-type controls, with 19 to 27 mice per group. In the LR3-treated 5XFAD mice the authors reported improved body composition (no detail is given in the abstract), but cognitive symptoms were not significantly altered across multiple assays. In the cortex, the researchers saw fewer filamentous plaques, more inert plaques and fewer low-molecular-weight amyloid-beta oligomers. The authors stated that the data do not support LR3 as a monotherapy per se, while arguing for further work on combination approaches (Engel et al., 2025). It is a mouse model of a disease, using a nasal route, so it says little about any other setting.

Human studies of mecasermin and related IGF-1 products (not LR3)

Because there are no LR3 trials, it is worth being clear about what human evidence on related molecules shows. All of the following concern mecasermin or a related IGF-1 product given by injection or infusion, and none concerns LR3.

• Rett syndrome phase 1 trial. Twelve girls with MECP2 mutations (nine with Rett syndrome) took part in a four-week multiple ascending dose period followed by a 20-week open-label extension. Twelve completed the first phase and ten the whole study, without evidence of hypoglycaemia or serious adverse events. Cerebrospinal fluid IGF-1 rose, and apnoea and some anxiety and mood measures improved during the open-label extension (Khwaja et al., 2014). The trial was small (12 participants), and the reported improvements in apnoea and mood and anxiety measures came from the open-label extension.
• Eu-IGFD registry. Among 306 children treated with mecasermin, 80 had at least one hypoglycaemia adverse event. Prior hypoglycaemia history and a Laron syndrome diagnosis were reported as predictors of hypoglycaemia events, and hypoglycaemia events ran at 0.11 per patient per treatment year, with serious events at 0.01 (Bang et al., 2023).
• Cochrane review in preterm infants. Two randomised trials with 140 infants tested intravenous IGF-1 given as mecasermin rinfabate, an IGF-1 product. All evidence was of very low certainty. For severe retinopathy of prematurity the risk ratio was 1.27 (95% CI 0.61 to 2.65), and, in the larger trial of 121 infants, for mortality 1.69 (95% CI 0.71 to 3.99). In the larger trial of 121 infants, the risk of one or more serious adverse events was higher with IGF-1, with a risk ratio of 1.28 (95% CI 1.01 to 1.62). The pooled estimate across both trials was a risk ratio of 1.18 (95% CI 0.94 to 1.47); the larger-trial figure came from a post-hoc sensitivity analysis, and the review authors concluded they could not draw conclusions (Trzaski et al., 2026).
• Review of mecasermin. A 2009 review reported hypoglycaemia as the most frequent side effect, along with lymphoid tissue hyperplasia, body-fat accumulation and coarsening of facial features, and noted that the anti-apoptotic properties of IGF-I are implicated in cancer, a concern for long-term therapy (Rosenbloom, 2009).

Safety signals reported in the literature

Several strands of evidence bear on safety, and none of them is a clinical safety assessment of LR3. A table of the adverse findings, with populations and designs, is in the side-effects section.

Glucose and insulin. In animals, LR3 lowered glucose and insulin in calves given it by injection (Hammon and Blum, 1998), reduced glucose in heifers (Hill et al., 1999) and lowered insulin in pigs (Dunaiski et al., 1997). In humans treated with mecasermin, hypoglycaemia is the most frequently reported side effect (Rosenbloom, 2009).

Cancer biology. A pooled analysis of 17 prospective and two cross-sectional studies, covering up to 10,554 prostate cancer cases and 13,618 controls, found that men in the highest versus the lowest fifth of circulating IGF-I had an odds ratio of 1.29 (95% CI 1.16 to 1.43) for prostate cancer in the prospective studies. The authors described strong evidence that IGF-I is highly likely to be involved in prostate cancer development (Travis et al., 2016). This concerns naturally occurring levels, not an analogue. A review of IGF-I and the gut described evidence from laboratory, animal and population studies as suggestive of a role in some cancers, with causality unproven (Howarth, 2003). Together with the tumour-bearing rat result above, these papers explain why mitogenic questions remain open.

Reported adverse effects in self-administration contexts. The 2026 narrative review of GH-IGF-1 axis "research compound" peptides, which includes IGF-1 Long R3, reports adverse effects spanning endocrine and metabolic disturbances (prolactin and cortisol elevations, appetite changes and dysglycaemia), fluid retention, muscle and joint pain, and injection-site reactions. It also notes that there is no regulatory approval for physique or performance use and that product composition in unregulated supply chains is uncertain. The abstract reports these across the whole class of peptides and does not attribute each effect to IGF-1 LR3 (Dominikowski et al., 2026).

Anti-doping research reviews. A 2009 review by Guha and colleagues said that, as growth-hormone tests develop, athletes were likely to turn to IGF-I, and that detection was a challenge for anti-doping organisations. It stated that the long-term effects of IGF-I administration are unknown but likely to resemble the adverse effects of chronic growth hormone abuse (Guha et al., 2009). These were background statements by the authors, not trial results on LR3. A 2013 review noted that no test was yet in place for detecting IGF-I misuse at that time, that IGF-I analogues were advertised online and available on the black market, and that a marker-based test was under development (Guha et al., 2013). Current detection capability was not verified for this article.

What the research does not tell us

A fair reading of the literature, including the IGF-1 LR3 animal studies above, leaves a long list of open questions.

• No human trials. No controlled human studies of IGF-1 LR3 were found in the records reviewed for this article. No human pharmacokinetic, dose-response or bioavailability data for it were found in the records reviewed, and none on muscle, fat or performance outcomes.
• Evidence hierarchy. The 2026 review ranks peptides from randomised-trial data down to no human studies (Dominikowski et al., 2026). Every LR3 paper above comes from animals, cells or laboratory chemistry, which is far from the human randomised-trial end of that range. The Cochrane review shows how even randomised IGF-1 trials can end with very low certainty (Trzaski et al., 2026).
• Species differences. Growth was restored in diabetic rats, not stimulated overall in guinea pigs, and inhibited in pigs. The papers do not show which of these patterns, if any, would resemble human biology.
• Route and formulation. Most evidence concerns injection, infusion, nasal delivery or cell culture. The one direct animal comparison among the studies reviewed here found no effect of fed LR3 on glucose and insulin in calves (Hammon and Blum, 1998), and the laboratory work shows pepsin cleaving LR3 (Bryant et al., 1996). The only positive oral-type result among the studies reviewed here is a local gut effect in artificially reared newborn rat pups. Whether intact LR3 survives the human gut and reaches the circulation is not known, and results cannot be assumed to apply to an oral capsule. For wider context on that question, see our article on whether oral peptides work.
• Long-term safety. Cancer risk with LR3 specifically was not found to have been studied in humans in the records reviewed for this article. The tumour-bearing rat data and the epidemiology of natural IGF-I levels are signals, not conclusions.
• Anecdotes. Forum and social-media accounts are not controlled data and are not used here.

IGF-1 LR3 results: what the studies actually measured

Anyone searching for IGF-1 LR3 results wants to know what happened when the analogue was tested. Each outcome below belongs to a named population of embryos, cells or animals, not to readers or any product, and no human trial of LR3 itself was found. Protocols are in the linked papers.

Growth and body weight. The outcome depended on the species. In streptozotocin-diabetic rats, LR3 and a second variant were reported to be 2.5 to 3 times more potent than natural IGF-I at restoring growth (Tomas et al., 1993). In female guinea pigs, a seven-day infusion did not significantly change weight gain or carcass composition, although adrenals, gut, kidneys and spleen formed a significantly larger fraction of body weight (Conlon et al., 1995). In finisher pigs in a four-day study, average daily gain and food intake fell (Dunaiski et al., 1997).

Hormones and metabolites. Mean plasma growth hormone fell by 23% in those pigs (Dunaiski et al., 1997). In neonatal calves, injected LR3 lowered plasma glucose and insulin, and fed LR3 had no effects (Hammon and Blum, 1998). In beef heifers on restricted feeding, an eight-hour intravenous infusion was followed by markedly lower plasma amino acids and glucose (Hill et al., 1999). In pigs and heifers alike, the animal's own circulating IGF-I fell during the infusion (Dunaiski et al., 1997; Hill et al., 1999).

Embryos and cells. In cultured bovine embryos, blastocyst total cell counts were 105 with LR3, 96 with IGF-I and 91 in controls (Prelle et al., 2001). In turkey muscle cells, a chicken version of LR3 was significantly less active than chicken IGF-I (Pesall et al., 2001).

Gut and brain. Newborn rat pups fed long R3 IGF-I showed the greatest villus height and cell counts of the groups compared (Staley et al., 1998). In Alzheimer's-model mice given intranasal LR3 for seven months, filamentous plaques were fewer, but cognition was not significantly altered (Engel et al., 2025).

Adverse findings and limits. In rats bearing a mammary tumour, tumour growth increased most with LR3 (Tomas et al., 1994); the side-effects section lists the rest. Most studies were short and each used a different species or model, and the abstracts offer only tentative explanations for why results differ (for example Conlon et al., 1995; Dunaiski et al., 1997), so the disagreement is unresolved. Among the records reviewed, the only direct comparison of fed and injected LR3 (calves) found no effect of fed LR3 on the plasma measures reported (Hammon and Blum, 1998), and the rat-pup diet study reported intestinal growth and local receptor and binding-protein markers rather than plasma or whole-body outcomes (Staley et al., 1998), so neither can be assumed to apply to an oral capsule.

IGF-1 LR3 side effects reported in the research

The table lists adverse or unfavourable findings, and other physiological changes that may bear on safety, in the records reviewed; the abstracts do not always describe these as adverse. None comes from a human study of LR3; each row describes only the named population. The narrative account of the animal findings is in the safety signals section.

One small trial found no evidence of hypoglycaemia or serious adverse events with mecasermin in 12 girls (Khwaja et al., 2014), so the picture varies between populations and products.

What case reports can and cannot show. None of the records reviewed is a case report of IGF-1 LR3 itself. A case report describes one person in one setting: it can flag that an event occurred, but not how often, whether the compound caused it, or what else the person was exposed to. The 2026 review adds that product composition in unregulated supply chains is uncertain (Dominikowski et al., 2026).

Data gaps. These records hold no human pharmacokinetic, dose-response, long-term safety or oral-capsule data for LR3. Mecasermin is a different molecule, so the infant and registry findings are not LR3 findings, and the table is not a prediction for any reader.

IGF-1 LR3 vs MK-677 vs HGH (somatropin): how they differ

These three act at different points of one hormone axis. Growth hormone (GH) stimulates liver synthesis of IGF-I (Rosenbloom, 2009). IGF-1 LR3 is an analogue of IGF-I itself, with high receptor affinity and low binding-protein affinity (Staley et al., 1998). MK-677 is an oral ghrelin mimetic that raised GH secretion in a randomised trial (Nass et al., 2008).

The evidence bases differ in kind. LR3 rests on animal, embryo and cell work. MK-677, as summarised in our MK-677 clinical trials article, has human randomised trials, though a 2018 review says few long-term, rigorously controlled studies of the secretagogue class exist (Sigalos and Pastuszak, 2018).

No head-to-head trial of IGF-1 LR3, MK-677 and growth hormone appears in the records reviewed, so this article does not rank them. The table shows differences in mechanism and type of evidence, not in outcome. The HGH column rests on reviews of growth hormone; the records reviewed hold no somatropin-specific study. This is general information, not legal or medical advice.

IGF-1 LR3 in the UK: legal and anti-doping status in brief

This is general information, not legal advice. It summarises verified statements from official sources, and each is limited to what the source says.

• Anti-doping. The WADA 2026 Prohibited List, in effect from 1 January 2026, names "Insulin-like growth factor 1 (IGF-1, mecasermin) and its analogues" under S2, peptide hormones, growth factors, related substances and mimetics, which are prohibited at all times, in and out of competition (WADA Prohibited List 2026). The list does not name LR3 specifically. Because LR3 is an IGF-1 analogue, it is understood to fall under that entry, but that is an inference. UK Anti-Doping explains that the List is updated each year and takes effect on 1 January, and that if a prohibited in-competition substance is found in an athlete's system they may face a ban regardless of when it was taken (UK Anti-Doping).
• Medicines law. Under regulation 46 of the Human Medicines Regulations 2012, a person may not sell or supply, or offer to sell or supply, an unauthorised medicinal product (regulation 46). Regulation 220 restricts the sale or supply of medicinal products that are not subject to general sale to registered pharmacy premises under pharmacist supervision (regulation 220).
• What counts as a medicine. According to the MHRA guidance linked here, a medicinal product is any substance presented as having properties of preventing or treating disease in human beings, or one that may be used by or administered to humans to restore, correct or modify a physiological function through a pharmacological, immunological or metabolic action (MHRA borderline products guidance). Whether a given product is a medicine is a question the MHRA decides on its presentation and function, so a label alone does not settle it. No authoritative UK page naming the legal classification of IGF-1 LR3 was found for this article.
• Enforcement. In a 2021 press release, the MHRA said that medicines without a marketing authorisation cannot be guaranteed to meet quality and safety standards, and it called selling unlicensed or prescription medicines a serious criminal offence (MHRA press release). That case concerned steroids and prescription medicines, not IGF-1 LR3.

Full breakdown with sources: Is IGF-1 LR3 legal in the UK?

About the Free Muscle IGF-1 LR3 listings

Free Muscle sells research compounds and gym apparel online at freemuscle.co.uk. The IGF-1 LR3 listing is the IGF-1 LR3, 60 capsules product page.

Research compounds sold by Free Muscle are supplied for laboratory research use only and are not for human consumption. They are not authorised as medicines by the MHRA, EMA or FDA, are not food supplements, and are sold only to adults aged 18 or over. Nothing on this page is medical or dosing advice.

• Batch testing. Every batch of research compounds is assayed for identity and purity by Janoshik Analytical, an independent laboratory. The Certificate of Analysis for a batch is sent on request: email the batch number printed on the label together with the product name. Details are on the lab tests page. For background, see our guides to reading a certificate of analysis and to Janoshik Analytical.
• Delivery. UK delivery is free and tracked, in plain packaging. Standard UK delivery takes 2 to 5 working days, and orders placed before 2pm UK time Monday to Friday are processed the same working day (shipping information).
• Returns. Unopened items in their original packaging can be returned within 30 days, as set out in the returns guarantee.
• Other listings. Browse the wider peptides collection for other research compounds.

Frequently asked questions

What is IGF-1 LR3?

It is a modified analogue of insulin-like growth factor 1, with arginine at position 3 and an N-terminal extension (Tomas et al., 1993), and with low binding-protein affinity (Staley et al., 1998). It has been used in cell-culture experiments (Prelle et al., 2001; Pesall et al., 2001) and in animal studies.

What does "long R3 IGF" mean?

"Long" refers to the N-terminal extension and "R3" to the arginine at residue 3. The same molecule appears in the literature as LR3-IGF-1, Long(R3)-IGF-1 and long R3 IGF-I.

How is IGF-1 LR3 different from natural IGF-1?

It was designed to have much lower affinity for IGF-binding proteins, measured as at least three orders of magnitude lower in one embryo-culture study (Prelle et al., 2001); one cell study found that such changes may also alter receptor binding (Pesall et al., 2001).

Has IGF-1 LR3 been tested in humans?

No human clinical trials of LR3 were found in the records reviewed for this article. The human clinical data found concern mecasermin or a related IGF-1 product given by injection or infusion, which are different molecules. The 2026 review of GH-IGF-1 axis peptides sorts them into evidence tiers running from randomised-trial data to a complete absence of human studies and names IGF-1 LR3 among the analogues it covers; its abstract does not say which tier LR3 sits in (Dominikowski et al., 2026).

Why do the route of administration and the formulation matter in research?

In calves, injected LR3 changed glucose and insulin while fed LR3 did not (Hammon and Blum, 1998). Results from one route cannot be assumed for another, including an oral capsule.

Why do IGF-1 LR3 animal studies disagree with each other?

The studies used different species, disease models, feeding states and infusion designs, so they are not directly comparable, and the abstracts reviewed here do not identify which factor explains the differences. Dunaiski et al. noted that analogues which stimulate growth in the rat inhibit it in the pig, and suggested that suppressed growth hormone may contribute in pigs (Dunaiski et al., 1997).

Is IGF-1 LR3 covered by anti-doping rules?

The WADA 2026 Prohibited List names IGF-1 and its analogues under S2, prohibited at all times. LR3 is not named individually, so its inclusion is an inference from "and its analogues". Athletes should check with UK Anti-Doping. This is general information, not legal advice.

What side effects of IGF-1 LR3 are reported in the research?

No human study of LR3 was found. In animals, reported findings include increased tumour growth in tumour-bearing rats (Tomas et al., 1994), reduced daily gain and growth hormone in pigs (Dunaiski et al., 1997), and lower glucose and insulin in calves given LR3 by injection (Hammon and Blum, 1998). A 2026 review lists endocrine, fluid-retention, muscle-pain and injection-site effects for the peptide class without attributing them to LR3 (Dominikowski et al., 2026). See the side-effects table.

What results did IGF-1 LR3 studies report?

Results differed by species and design: growth was restored in diabetic rats (Tomas et al., 1993), not stimulated overall in guinea pigs (Conlon et al., 1995) and reduced in pigs (Dunaiski et al., 1997). Embryo and cell studies also reported different patterns (Prelle et al., 2001; Pesall et al., 2001). These are findings for the named animals and cells, and the results section sets them beside the adverse findings. Adverse findings in the same literature include increased tumour growth in tumour-bearing rats (Tomas et al., 1994) and lower daily gain in pigs (Dunaiski et al., 1997); see the side-effects section.

How does IGF-1 LR3 compare with HGH and MK-677?

They act at different points of the GH-IGF-1 axis. LR3 is an IGF-I analogue, MK-677 is an oral ghrelin mimetic (Nass et al., 2008), and growth hormone stimulates liver IGF-I synthesis (Rosenbloom, 2009). No head-to-head trial was found, so none is ranked above another. See the comparison table, our MK-677 article and our HGH article.

What is the half-life of IGF-1 LR3?

No half-life figure for LR3 appears in the abstracts reviewed for this article, and no human pharmacokinetic data were found. The papers do report that circulating natural IGF-I fell during LR3 infusion in pigs and heifers (Dunaiski et al., 1997; Hill et al., 1999).

Is IGF-1 LR3 legal in the UK?

This article found no authoritative UK page naming the legal classification of IGF-1 LR3. Under regulation 46 of the Human Medicines Regulations 2012, an unauthorised medicinal product may not be sold or supplied, and whether a product is a medicine is a matter for the MHRA. Free Muscle has a separate UK legal status guide, which is general information only. This is general information, not legal advice.

Is IGF-1 misuse tested for in sport?

WADA's 2026 list names IGF-1 and its analogues under S2, prohibited at all times. Athletes should check with UK Anti-Doping. As historical background, a 2013 review said no test was yet in place for IGF-I misuse, while a marker-based test was under development (Guha et al., 2013). Current detection capability was not verified for this article.

Does this article give instructions or doses for IGF-1 LR3?

No. This article publishes no dosing or protocol. IGF-1 LR3 is sold for laboratory research use only, to customers aged 18 or over, and nothing here is medical advice. The protocols used in the animal and cell studies are in the linked papers.

Where can I see a batch certificate for a Free Muscle research compound?

Email the batch number printed on the label with the product name, and the Certificate of Analysis from Janoshik Analytical is sent on request. The lab tests page explains the process.

Related reading

• Short overview: IGF-1 LR3: a cell-culture reagent, not a supplement

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