Editorial note: this article summarises published research on IGF-1 analogues. Baclabs does not sell IGF-1 LR3, IGF-1 DES or any peptide; we supply bacteriostatic water and reconstitution consumables. Nothing here is medical advice.
IGF-1 LR3 and IGF-1 DES are two engineered versions of insulin-like growth factor 1, both built to solve the same problem: native IGF-1 is almost entirely captured by IGF binding proteins (IGFBPs) as soon as it enters circulation, leaving very little free to activate receptors. LR3 solves it by adding bulk to the N-terminus; DES solves it by cutting three residues off. The consequences for duration, distribution and risk are not the same.
This article compares the two on structure, binding protein affinity and reported persistence, sets the widely repeated “bodybuilding protocol” figures against the only licensed IGF-1 product’s actual dosing, and is explicit about what has and has not been tested in humans. Short version: the structural and cell-culture pharmacology is real and published; the human hypertrophy evidence does not exist.
What IGF-1 LR3 actually is
Long R3 IGF-1 carries two modifications to the mature 70-amino-acid IGF-1 sequence. First, arginine replaces glutamate at position 3. Second, a hydrophobic 13-amino-acid extension is fused to the N-terminus, taking the chain from 70 to 83 residues. The analogue was designed and characterised by Francis and colleagues in Adelaide in 1992, who concluded that its enhanced potency came from reduced IGF-binding-protein capture rather than tighter receptor binding [3]. Later work from the same group measured the scale of that change: native IGF-1 binds IGFBP-3, IGFBP-4 and total rat plasma binding proteins with roughly 1,000-fold higher affinity than LR3, which in cultured L6 myoblasts translates into a 5- to 10-fold potency advantage for the analogue [8].
The best-known in vivo work is a guinea pig infusion study published in the Journal of Endocrinology in 1995. Long R3 IGF-I significantly increased the fractional weight of adrenals, gut, kidneys and spleen, while total circulating IGF concentrations were not increased by treatment [1]. Two things are worth pulling out of that: the responding tissues were viscera rather than skeletal muscle, and the analogue’s escape from binding proteins did not manifest as a higher measured IGF pool.
What IGF-1 DES actually is
Des(1-3)IGF-1 is the naturally occurring truncated form of IGF-1, lacking the N-terminal tripeptide Gly-Pro-Glu, probably produced by post-translational cleavage. It has been isolated from bovine colostrum, human brain and porcine uterine tissue. Because the glutamate at position 3 is gone, IGFBP binding falls sharply, and des(1-3)IGF-I is generally about 10-fold more potent than IGF-I at stimulating hypertrophy and proliferation of cultured cells [2].
DES is a smaller molecule than native IGF-1, not a larger one. That is the structural basis of the common claim that DES acts locally and briefly while LR3 acts systemically and for longer, a smaller, unbound growth factor with no half-life-extending modification would be expected to clear faster. That expectation is reasonable; it is not the same as a measured human pharmacokinetic profile, which does not appear to have been published for either analogue.
IGF-1 LR3 vs IGF-1 DES: the comparison table
| IGF-1 LR3 | IGF-1 DES | |
|---|---|---|
| Modification | Arg for Glu at position 3, plus 13-residue N-terminal extension [3] | N-terminal Gly-Pro-Glu tripeptide removed [2] |
| Chain length | 83 residues (70 + 13) [3] | 67 residues (70 − 3) [2] |
| IGFBP affinity | ~1,000-fold lower than IGF-1 [8] | Considerably reduced [2] |
| Relative in vitro potency | 5- to 10-fold greater than IGF-1 in L6 myoblasts [8] | ~10-fold greater than IGF-1 in cultured cells [2] |
| Occurs naturally | No, engineered | Yes, colostrum, brain, uterus [2] |
| Published human hypertrophy trial | None located | None located |
The IGF-1 LR3 bodybuilding protocol question
Search demand for an “IGF-1 LR3 bodybuilding protocol” is substantial, so it deserves a direct answer rather than a dodge.
What circulates on forums and vendor pages is a cluster of claims, not data: daily microgram-scale LR3 doses over multi-week cycles, sometimes split across injection sites, and DES claimed as a pre-workout injection on the argument that its short action confines the effect to the trained muscle. These figures are unattributed community claims, and we do not reproduce them. We could not identify a peer-reviewed trial, a registry entry or a pharmacokinetic study in humans that generated any of them. They are not derived from dose-finding work, and there is no published human safety margin for them.
The contrast with the licensed comparator is stark. Mecasermin (Increlex) is recombinant human IGF-1, authorised for long-term treatment of growth failure in children and adolescents aged 2 to 18 with confirmed severe primary IGF-1 deficiency. Its dosing is 0.04 mg/kg twice daily to start, with an explicit ceiling: doses greater than 0.12 mg/kg twice daily should not be exceeded [4]. Terminal half-life after a single 0.12 mg/kg subcutaneous dose was approximately 5.8 hours in that paediatric population [4].
So the only IGF-1 product with an authorised dose is dosed by body weight, twice daily, with a hard maximum, under supervision, for a rare deficiency state. The analogues sold online are not that product, are engineered specifically to be less restrained than that product, and are dosed by figures nobody can source.
Hypoglycaemia is the concrete risk
IGF-1 shares substantial structural homology with insulin and activates overlapping downstream signalling. The Increlex product information treats hypoglycaemia as the central hazard: administration must occur shortly before or after a meal or snack, patients are told to avoid high-risk activities for 2–3 hours after dosing, and carers are trained to recognise severe episodes and administer glucagon [4].
Other documented effects include tonsillar hypertrophy in 9% of trial subjects, injection-site lipohypertrophy in 17%, headache in 44%, vomiting in 26%, intracranial hypertension in around 1%, and post-marketing reports of benign and malignant neoplasms [4][6]. An analogue designed to escape the binding proteins that buffer free IGF-1 has no reason to be gentler, and comes with no titration schedule or monitoring framework.
The neoplasia concern deserves naming: IGF-1 receptor signalling is mitogenic and anti-apoptotic, which is precisely why it drives growth. Chronic supraphysiological stimulation of that pathway in adults has not been studied for cancer risk.
Anti-doping and UK legal status
IGF-1 (mecasermin) and its analogues are named in WADA section S2, prohibited at all times and classed as non-specified substances [5][7]. Neither IGF-1 LR3 nor IGF-1 DES holds a UK marketing authorisation. Supplying either for human use engages the Human Medicines Regulations 2012 and falls within MHRA enforcement; material sold as “research use only” is not exempt from that framework once it is intended for a person.
Reconstitution and diluent choice
Both analogues are supplied lyophilised, typically in 1 mg vials, and require reconstitution before any laboratory use. The arithmetic is the same as for any peptide: concentration = milligrams in the vial ÷ millilitres of diluent, and on a U-100 insulin syringe each unit is 0.01 mL, so one unit carries the concentration divided by 100. Because the working quantities for IGF-1 analogues are in micrograms, a 1 mg vial is normally diluted more generously than a 5 mg or 10 mg vial of a GH secretagogue would be.
| Diluent added to 1 mg | Concentration | Per unit (U-100) | Units for 20 mcg | Units for 50 mcg |
|---|---|---|---|---|
| 1 mL | 1 mg/mL (1,000 mcg/mL) | 10 mcg | 2 | 5 |
| 2 mL | 0.5 mg/mL (500 mcg/mL) | 5 mcg | 4 | 10 |
Worked example: 1 mg + 2 mL bacteriostatic water = 0.5 mg/mL = 500 mcg/mL; each unit on a U-100 syringe holds 5 mcg, so 10 units contain 50 mcg. The quantities in the table are for illustrating the arithmetic, not a dosing recommendation; as discussed above, no human dose for either analogue has been established.
IGF-1 analogues are relatively fragile proteins: they should not be shaken, and the diluent should be run down the vial wall rather than jetted onto the cake. Multi-dose vials need a preserved diluent so that repeated punctures do not seed bacterial growth. Baclabs supplies UK-stocked bacteriostatic water in 30 mL vials; the reconstitution guide covers the concentration arithmetic, bacteriostatic vs sterile water covers when a preservative is appropriate, and storage and shelf life explains the 28-day rule after first puncture.
For context on where these analogues sit relative to somatropin and myostatin regulators, see the muscle growth peptides hub. For the closely related IGF-1 splice-variant fragment, see MGF vs PEG-MGF.
Frequently asked questions
What is the difference between IGF-1 LR3 and IGF-1 DES?
LR3 adds a 13-amino-acid N-terminal extension and swaps arginine for glutamate at position 3, producing an 83-residue analogue with roughly 1,000-fold lower IGFBP affinity and longer persistence [3][8]. DES removes the first three residues (Gly-Pro-Glu), giving a smaller, naturally occurring form that is roughly ten times more potent than IGF-1 in cell culture but has no half-life extension [2].
What is the half-life of IGF-1 LR3?
No published human pharmacokinetic study of IGF-1 LR3 could be located. The rat work shows that reduced binding-protein capture changes plasma clearance relative to native IGF-1 [8]. For scale, licensed recombinant IGF-1 (mecasermin) has a terminal half-life of about 5.8 hours after a 0.12 mg/kg subcutaneous dose [4]. Widely quoted LR3 half-life figures of 20–30 hours are community claims, not measured values.
Is there an evidence-based IGF-1 LR3 bodybuilding protocol?
No. The daily dose ranges repeated on forums and vendor pages have no traceable source. There is no published controlled human trial of IGF-1 LR3 for hypertrophy, no dose-finding study and no safety data at those exposures. The only IGF-1 dosing supported by regulatory review is mecasermin at 0.04–0.12 mg/kg twice daily for severe primary IGF-1 deficiency [4].
Does IGF-1 DES cause localised muscle growth?
The idea rests on DES clearing quickly and so acting near the injection site. That is a plausible inference from its structure, but it has not been demonstrated in humans. The one in vivo study we located for an IGFBP-evading analogue found increased weights of adrenals, gut, kidneys and spleen rather than skeletal muscle [1].
Can IGF-1 analogues cause hypoglycaemia?
Yes, that is the expected class effect. The licensed IGF-1 product carries detailed hypoglycaemia warnings including meal timing, a 2–3 hour restriction on high-risk activity after dosing, and glucagon training for carers [4]. Analogues engineered to evade binding proteins would be expected to raise free IGF-1 activity further, with no established titration or monitoring framework.
References
- Long R3 insulin-like growth factor-I (IGF-I) infusion stimulates organ growth but reduces plasma IGF-I, IGF-II and IGF binding protein concentrations in the guinea pig. Journal of Endocrinology, 1995
- Des(1-3)IGF-I: a truncated form of insulin-like growth factor-I. Cytokine & Growth Factor Reviews, 1996
- 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. Francis GL et al. Journal of Molecular Endocrinology, 1992
- Increlex (mecasermin) Summary of Product Characteristics. European Medicines Agency
- WADA Prohibited List S2: Peptide hormones, growth factors, related substances and mimetics. Drugs.com summary of the WADA list
- INCRELEX (mecasermin) injection, for subcutaneous use, US prescribing information. FDA, 2025
- The Prohibited List. World Anti-Doping Agency
- Effects of interactions between IGFBPs and IGFs on the plasma clearance and in vivo biological activities of IGFs and IGF analogs. Growth Regulation, 1993
Disclaimer: This content is for educational purposes only and does not constitute medical advice. Bacteriostatic water is supplied for reconstitution of substances intended for research and for use as directed by a healthcare professional. Peptides and medicines discussed here may be unlicensed in the UK or prescription-only; consult a qualified clinician before using any medicine. Baclabs does not sell peptides.