IGF-1 LR3
Long R3 Insulin-Like Growth Factor-1
Evidence grade 1 of 5, Untested. Read how the Atlas grades evidence.
Long R3 IGF-1 was engineered as a cell-culture supplement for bioprocessing, not as a human therapeutic, and it carries no human efficacy or safety trials for muscle growth or any clinical indication. Its use in bodybuilding rests on the known anabolic biology of native IGF-1 plus anecdote, so it grades grade 1 (animal and in-vitro rationale only), well below the FDA-approved recombinant IGF-1 drug mecasermin, which is a separate product approved only for severe primary IGF-1 deficiency in children.
- FDA
- Not approved for human use. Sold as a cell-culture research reagent labeled not for human consumption. The only FDA-approved recombinant IGF-1 is the separate native-sequence drug mecasermin (Increlex), approved in 2005 solely for severe primary IGF-1 deficiency in children.
- WADA
- Prohibited at all times under WADA S2.3 (growth factors); IGF-1 and its analogues are named on the list.
Reference only. Not medical advice.
What can go wrong
No human safety data; cancer-promotion concern given IGF-1 is associated with higher colorectal, breast, prostate and thyroid cancer risk; hypoglycemia; unapproved research-only material.
Talk to a clinician before taking this, particularly if you have any history of cancer. The Atlas can tell you what has been studied about IGF-1 LR3. It cannot tell you how it would interact with your body, your history, or anything else you are taking, and nothing on this page is a reason to start.
A modified IGF-1 with an extended half-life that acts downstream of growth hormone, directly stimulating muscle protein synthesis. A potent anabolic agent used mostly in bodybuilding, with a notably more concerning risk profile than the GH secretagogues.
A direct anabolic signal that skips the pituitary. Serious risk profile.
What people take it for
These are the reasons people give for taking it. They are not effects it has been shown to have.
How it is supposed to work
IGF1-LR3 is a long-acting, modified form of IGF-1, the growth factor that carries out much of what growth hormone does. It binds the IGF-1 receptor on muscle and connective tissue and switches on the pathways that build muscle: protein synthesis, the activation of muscle stem cells, and fiber growth, while also blocking muscle breakdown. Its engineering, an amino-acid swap plus an added tail, makes it last far longer than natural IGF-1 and slip past the proteins that normally keep IGF-1 in check, so it stays active and free for about a day. The catch is that IGF-1 is a general growth signal, and it does not only grow muscle.
IGF1-LR3 (Long R3 IGF-1) is an 83-amino-acid analog of IGF-1 with an arginine substituted at the third position and a 13-amino-acid extension added to one end. Those changes do two things: they extend its active life from minutes to roughly a day, and they lower its binding to the carrier proteins that restrain IGF-1, leaving more of it free and active. It is a recombinant protein, originally created as a research reagent before bodybuilding adopted it.
- Type
- Modified IGF-1 (83 aa)
- Acts on
- IGF-1 receptor
- Half-life
- ~20-30 hours
- Effect
- Muscle growth
- Approved
- No (research chemical)
- WADA
- Prohibited (S2)
It Grows More Than Muscle
IGF1-LR3 does build muscle, but the honest danger is that IGF-1 is a general grow-and-divide signal that cannot be aimed only at muscle, and that has three serious consequences. First, cancer: IGF-1 drives cell proliferation, higher IGF-1 levels are epidemiologically linked to colorectal, breast, prostate and thyroid cancers, and the IGF-1-excess condition acromegaly carries elevated cancer mortality, so chronically raising IGF-1 carries a real, mechanism-based cancer concern, especially with any tumor history. Second, acromegaly-like overgrowth: too much IGF-1 can enlarge the hands, feet and jaw, thicken soft tissue, and even enlarge internal organs. Third, low blood sugar: being insulin-like, it can drop glucose dangerously. On top of all that, there is very little human research on LR3 specifically, it is banned in sport, and it is an unapproved research chemical of uncertain quality.
Safety in detail
There are no human efficacy or safety trials of Long R3 IGF-1 for muscle growth or any indication, so its risk profile is inferred from IGF-1 biology and the mecasermin label rather than measured in users. The chief documented concern is that sustained high IGF-1 exposure is associated with increased risk of several cancers, alongside hypoglycemia; the material is a research reagent not manufactured or tested for human injection.
- The central concern is cancer: IGF-1 promotes cell proliferation and is epidemiologically tied to several cancers, so it should be avoided by anyone with a personal or family history of tumors.
- Sustained high doses can produce acromegaly-like overgrowth of bones (hands, feet, jaw), thickened tissue and even organ enlargement.
- Because it is insulin-like, it can cause hypoglycemia, sometimes dangerously.
- Its long half-life can desensitize IGF-1 receptors over time, which is why users cycle it.
- Joint pain, nerve compression, swelling, headaches and injection-site reactions are reported.
- It is prohibited in sport, is an unapproved research chemical, and gray-market product has uncertain identity and purity.
Children and teenagers
The only legitimate pediatric IGF-1 use is mecasermin for a rare severe IGF-1 deficiency, given under pediatric endocrinology. Gray-market IGF1-LR3 for muscle has no place in anyone under 18; manipulating IGF-1 in a developing body is especially dangerous given its growth and cancer implications. Any pediatric IGF-1 therapy belongs strictly with specialists, never self-sourced.
What people get wrong
Nothing recorded here yet. There is almost certainly something people get wrong about this one, and the blank space means we have not written it down, not that the record is clean.
Who profits, and who pushes back
Nobody is named here yet, because we have not done that work on this entry. Read that as unfinished. Somebody almost certainly sells this, and somebody almost certainly disputes it. Assume both until we have checked.
IGF1-LR3 has no legitimate product behind it; the only approved IGF-1, mecasermin, is a separate rare-disease drug. Its market is gray: research-peptide vendors selling recombinant IGF1-LR3 and bodybuilding coaches and influencers promoting it as a potent muscle builder. The muscle-building marketing is loud, while the cancer and overgrowth risks, and the near-total absence of human data on the compound itself, go largely unmentioned.
How we got here
Long R3 IGF-1 began as a protein-engineering solution for biomanufacturing, not medicine. The native IGF-1 sequence was modified with an Arg-for-Glu swap at position 3 and a 13-residue N-terminal extension to extend half-life and lower binding-protein affinity, producing a supplement that boosts recombinant-protein yield in mammalian cell culture. It was commercialized as LONG R3 IGF-I through GroPep in Australia and later carried under Novozymes/Sigma and now Repligen for bioprocessing. Because that same longer-acting anabolic biology attracted bodybuilders, research-chemical vendors began reselling the E. coli reagent as an injectable performance peptide labeled not for human consumption, a repurposing that sits well apart from the separately approved native rhIGF-1 drug mecasermin (Increlex).
IGF1-LR3 began as a research reagent, a long-acting, binding-protein-resistant form of IGF-1 useful for cell-culture work. As IGF-1’s central role in growth hormone’s muscle effects became clear, and as recombinant IGF-1 (mecasermin) was approved for a rare childhood deficiency, the bodybuilding world adopted IGF1-LR3 as a potent anabolic. It spread through gray-market and research-chemical channels, its muscle reputation growing even as the cancer and overgrowth concerns inherent to elevating IGF-1, and the lack of human data on the compound itself, remained largely in the background.
- 1980s-1990sIGF-1 biology established as the mediator of much of growth hormone’s effect; IGF1-LR3 created as a long-acting research reagent.
- 2000sRecombinant IGF-1 (mecasermin) approved for a rare childhood IGF-1 deficiency.
- 2000s-2010sBodybuilding adopts IGF1-LR3 as a potent anabolic research chemical.
- 2010s-2020sPersistent gray-market use; IGF-1-cancer epidemiology sharpens the risk picture.
The numbers behind the grade
- Type
- Modified IGF-1
- Action
- Muscle growth
- Half-life
- ~20-30 hours
- Approved
- No
- WADA
- Prohibited (S2)
- Key risks
- Cancer, acromegaly
The people taking it
A long-standing and popular bodybuilding anabolic peptide, one of the core muscle-building research chemicals, known for potent effects and for serious, often-underestimated risks.
IGF1-LR3’s users are overwhelmingly bodybuilders and strength athletes seeking muscle growth and recovery, plus a broader anabolic and performance crowd and some anti-aging users drawn by IGF-1’s decline with age. It is a committed enhancement-user compound, not a wellness one, and its appeal rests on potent muscle effects while its serious risks are widely underappreciated.
Used gray-market in bodybuilding for muscle growth and recovery, on rodent data and IGF-1 biology rather than human trials. Not approved, banned in sport, and carrying serious growth-related risks.
Set against the alternatives
Against growth hormone, which sits upstream and raises IGF-1 while doing more besides, IGF1-LR3 delivers IGF-1 directly and lasts longer, but both carry the IGF-1-mediated risks, and some argue growth hormone is the more powerful tool. Against IGF-1 DES, a related variant that is shorter-acting but even more potently anabolic, the two hit the same receptor with different profiles. The crucial comparison, though, is to mecasermin, the FDA-approved recombinant IGF-1: it is a tightly supervised treatment for a rare childhood growth disorder, the legitimate face of IGF-1 therapy, and the opposite of unsupervised muscle use. And against Follistatin, the other anabolic peptide, IGF1-LR3 works by stimulating growth signaling rather than removing a brake. Its muscle effect is real; its inability to confine that growth is the problem.
What we do not know
- What the real cancer risk of chronically elevating IGF-1 is in users, given the strong mechanistic concern.
- How its effects and dangers differ from native IGF-1, with so little LR3-specific human data.
- Whether any muscle benefit could justify the growth and cancer risks.
- How much gray-market product is even genuine, active protein.
What could change
IGF-1 and cancer researchContinued work on how elevated IGF-1 affects cancer risk bears directly on its safety.Authenticity scrutinyGrowing awareness that much gray-market recombinant product may be substandard or fake.The approved contrastMecasermin remains the only legitimate IGF-1 therapy, underscoring how far muscle use departs from medicine.Persistent demandBodybuilding interest endures despite the risk profile.
Legal status
IGF1-LR3 is not approved for human use and is sold as a research chemical, not for human consumption, in the US and most countries. It is used gray-market by bodybuilders and is banned in sport. The only approved IGF-1 therapy is mecasermin, a prescription drug for a rare childhood condition, which is unrelated to muscle use.
Status current as of July 2026. Regulatory positions change, sometimes quickly.
The market for this
What follows describes how this is bought and sold. It is not a buying guide and it is not an endorsement of any seller.
There is no approved way to obtain IGF1-LR3 for muscle; it is sold only as research-use-only material, which is not for human use, is banned in sport, and has uncertain quality. Given the cancer, overgrowth and hypoglycemia risks, the honest guidance is to avoid it; the approved IGF-1 drug is reserved for a specific rare disease under specialist care.
Gray-market vials are priced like other research peptides, but for a recombinant protein the low cost is a warning sign for authenticity and potency. There is no legitimate product to price against for muscle use.
Almost all IGF1-LR3 is recombinantly produced overseas, predominantly in China, and sold as research material with no quality assurance and a real chance the product is not genuine, active protein. A certificate of analysis is the minimum check and cannot fully validate a recombinant protein.
China and research vendorsThe dominant source of recombinant IGF1-LR3, sold as research-use-only material, with real questions about whether vials contain genuine, active protein.Authenticity concernsAs a recombinant protein, it is harder to verify than a simple peptide, so quality and potency vary widely.No legitimate channelThe approved IGF-1 drug runs through an entirely separate, regulated rare-disease pathway.
At a glance
- Action
- Downstream of GH
- Half-life
- Extended vs native IGF-1
- Use
- Elite bodybuilding
- Risk
- Hypoglycemia, cancer promotion
What this entry does not yet cover
What follows is unfinished work on our side, not a finding about IGF-1 LR3.
Nothing outstanding on this one.
Sources
Long R3 IGF-1 is a recombinant IGF-1 analog engineered and sold as a cell-culture supplement for bioprocessing, marketed for research rather than human therapeutic use
LR3 IGF-1 is an 83-amino-acid analog with an Arg substitution at position 3 and a 13-residue N-terminal extension, giving longer half-life and low IGFBP affinity; produced in E. coli and supplied as a research protein for cell culture
LONG R3 IGF-I improves CHO cell-culture volumetric productivity by up to 62 percent over unsupplemented culture, confirming its intended role as a bioprocessing reagent
Exogenous IGF-1 and its analogues are prohibited at all times under WADA Prohibited List section S2, growth factors sub-class S2.3
S2.3 of the WADA list names Insulin-like growth factor 1 (IGF-1, mecasermin) and its analogues as prohibited growth factors at all times in and out of competition
Drugs.com, WADA S2 Peptide Hormones, Growth Factors and Related Substances
The only FDA-approved recombinant human IGF-1 product is mecasermin (Increlex), approved 30 August 2005 solely for growth failure in children with severe primary IGF-1 deficiency, a separate product from the unapproved LR3 analog
Increlex (mecasermin) label confirms rhIGF-1 is indicated only for severe primary IGF-1 deficiency, with hypoglycemia and neoplasia among labeled warnings, underscoring that no IGF-1 product is approved for muscle growth
A UK Biobank analysis of roughly 400,000 people, published in Cancer Research, found higher circulating IGF-1 associated with increased risk of colorectal, breast, prostate and thyroid cancer
Pooled analysis of 17 prospective studies (4,790 cases) found women with high circulating IGF-1 had about 30 percent higher breast-cancer risk than women with low IGF-1
Endogenous Hormones and Breast Cancer Collaborative Group, Lancet Oncology (PMC)
IGF-1 signaling is mitogenic and anti-apoptotic and promotes cell-cycle progression, angiogenesis and metastasis, the mechanistic basis for the cancer-promotion concern with sustained IGF-1 exposure
Review of GH, GH secretagogues and IGF-1 in sport confirms IGF-1 and analogues are prohibited and details detectability and therapeutic-use-exemption context
Growth hormone, secretagogues and IGF-1 in sports, ScienceDirect
The studies that matter
Rodent anabolic studiesvarious
IGF1-LR3 is reported to be roughly 2.5 times more muscle-building than native IGF-1 in rodents, acting through the IGF-1 receptor and Akt pathway to drive hypertrophy and muscle stem-cell proliferation.
LR3-specific human dataminimal
Very few studies examine IGF1-LR3 itself in humans, so its risks are largely extrapolated from IGF-1 biology rather than directly measured.
IGF-1 and cancer epidemiology2000s-2020s
Higher circulating IGF-1 is associated with increased risk of several cancers, including colorectal, breast, prostate and thyroid, in the general population.
Acromegaly outcomesvarious
Chronic IGF-1 excess, as in acromegaly, is linked to elevated rates of tumors and is a leading contributor to mortality, a warning about sustained IGF-1 elevation.
Approved IGF-1 (mecasermin)established
Recombinant IGF-1 is FDA-approved as mecasermin for a rare severe childhood IGF-1 deficiency, the only legitimate IGF-1 therapy, and very different from bodybuilding use.