Is IGF-1 LR3 legal?
Not FDA approved- FDA status
- IGF-1 LR3 is not FDA approved and is not on FDA’s 503A bulks list.
- Compounding
- US compounding pharmacies cannot routinely prepare it.
- Prescription
- There is no approved US prescription product for IGF-1 LR3.
- Online market
- Products sold online are labelled “for research use only”: not made, tested or labelled for human use, and often mislabelled.
- Sport
- Prohibited in sport under the World Anti-Doping Agency list.
US status checked October 2026 against FDA’s compounding lists. Sources at the foot of the page.
What is IGF-1 LR3?
IGF-1 LR3, also called Long R3 IGF-1, is an engineered version of insulin-like growth factor 1 (IGF-1). IGF-1 is the hormone that carries out much of growth hormone's effect on tissue growth. LR3 was designed so that it lasts longer and acts more strongly than the natural hormone.
It was developed in Australia as a supplement for cell culture, where it helps cells grow in industrial and laboratory settings. It is still sold mainly for that purpose, and labs continue to work on cheaper ways to produce it.1 Outside the lab, it is marketed online to bodybuilders for muscle growth and recovery. It is not an approved drug, and no clinical trial has tested it in people.5
- Anecdotal only
- In vitro only
- Animal models only
- Preliminary human
- Clinical trials
- Regulator approved
How IGF-1 LR3 works
Natural IGF-1 is mostly held in the blood by binding proteins, which act as a reservoir and limit how much reaches cells. IGF-1 LR3 is built to slip past those proteins. Two changes do this. One amino acid near the start is swapped, and a short extra chain of amino acids is added to the front. The result binds poorly to the binding proteins but still activates the IGF-1 receptor on cells.
Because more of it is free, it acts more strongly. Because it is not cleared as fast as free natural IGF-1, it stays active for many hours rather than minutes.
In more precise terms, LR3 replaces glutamic acid with arginine at position 3 and adds a 13-amino-acid extension at the N-terminus. It keeps full activity at the type 1 IGF receptor, which drives protein synthesis and cell proliferation through the PI3K-Akt and MAPK pathways. It also has some affinity for the insulin receptor, which explains its blood-sugar-lowering effect. In mouse macrophage precursors, LR3 behaved differently from native IGF-1, in part because it escaped a binding protein that the cells were secreting.6
IGF-1 analogues act at the end of the axis, directly on tissues, bypassing the pituitary and the liver.
What the research shows on IGF-1 LR3
Every published study of IGF-1 LR3 is in cells or animals. There are no human trials for muscle growth, recovery, fat loss or any other outcome. A 2026 review of performance-enhancing peptides that act on the growth hormone axis placed IGF-1 analogs among compounds with little or no human evidence, and stressed uncertainty about the products themselves.5
The animal work is varied. In mice prone to atherosclerosis, LR3 reduced narrowing of the arteries and made plaques more stable.2 In a mouse model of Alzheimer's disease, seven months of nasal LR3 improved body composition and changed plaque structure in the brain, but it did not protect memory or behavior.4 Researchers have also attached chemotherapy to LR3 to carry the drug into cancer cells, because many cancers carry extra IGF-1 receptors.3
That last point cuts both ways. The same paper notes that the IGF-1 receptor is overexpressed on many cancer cells and is linked to spread and resistance to cell death.3 A compound that strongly activates this receptor for many hours is a reasonable concern for anyone with an undiagnosed tumor.
The mouse results also show how hard it is to predict benefit. In the Alzheimer's model, LR3 changed brain tissue in ways that looked favorable under the microscope yet did not change the outcome that mattered.4 None of these studies looked at muscle growth in healthy adults. Claims about hypertrophy and fiber growth in humans rest on cell work and anecdote, not trials.
Studied for: Muscle hypertrophy research, Cell-culture growth supplement, Recovery.
IGF-1 LR3 reference data
| Molecular weight | 9,111 Da |
|---|---|
| CAS number | 946870-92-4 |
| FDA status | Not approved for any indication. |
| Prohibited in sport | Yes, under the WADA prohibited list |
IGF-1 LR3 dosage in published research
Once daily · usually run for about 4 weeks. A reference pattern, not a prescription.
Open this in the dosage calculator ↗
How IGF-1 LR3 is used in practice
In legitimate settings, IGF-1 LR3 is a cell-culture reagent. It is not part of approved clinical care, and reputable telehealth services and compounding pharmacies do not offer it.
In bodybuilding, it is bought online as a "research use only" powder, mixed with bacteriostatic water and injected, usually once a day in short cycles. Some users inject it near a target muscle. These practices come from forums and seller guidance rather than studies.
Product quality is a serious issue. LR3 is a large, folded protein of 83 amino acids. Making it correctly and keeping it stable takes proper manufacturing and cold storage. Online products are not made to pharmaceutical standards, and their identity, dose and sterility are unverified.5 IGF-1 and its analogs are prohibited in sport.
IGF-1 LR3 risks and side effects
Low blood sugar is the most predictable acute risk, because LR3 acts partly like insulin and lasts many hours. Symptoms range from shakiness and sweating to confusion and loss of consciousness. The risk rises with fasting, heavy training and use alongside insulin or diabetes drugs. Reported adverse effects of GH-axis peptides also include fluid retention, joint and muscle pain and injection-site reactions.5 Users also describe headache and jaw pain.
The longer-term concern is unwanted growth. The worry that IGF-1 analogs could promote tumors is biologically plausible but unproven in humans.5 People with active or suspected cancer should not use it. It should also be avoided in pregnancy and by people with diabetes.
There are no human data on safe doses, long-term effects or drug interactions. Non-sterile products add the risk of infection and immune reactions.
Reported side effects
Alternatives to IGF-1 LR3
For muscle growth, progressive resistance training with adequate protein, calories and sleep remains the best-supported approach. For diagnosed hormone problems, approved treatments exist: testosterone for confirmed male hypogonadism, recombinant growth hormone for growth hormone deficiency, and mecasermin (Increlex), a recombinant IGF-1, for children with severe primary IGF-1 deficiency.
For recovery, sleep, nutrition and planned rest days have more support than any unapproved compound. Anyone curious about their own IGF-1 can have it measured with a simple blood test, and an abnormal result deserves a proper medical workup. Mecasermin is the closest approved relative. It shows what IGF-1 therapy looks like with proper oversight: its label lists active or suspected cancer as a contraindication, and it requires careful monitoring for low blood sugar.
The bottom line on IGF-1 LR3
IGF-1 LR3 is a well-established lab reagent and an untested human drug. It reliably activates the IGF-1 receptor for a long time, which is exactly why low blood sugar and unwanted tissue growth are real concerns. With no human trials and unverified products, the risks are easier to define than the benefits.
Questions for a clinician
- What evidence applies to my situation, and at what level?
- What established alternatives should I consider first?
- What monitoring would be necessary, and how often?
- Can this be prescribed at all where I live, or only sold for research?
IGF-1 LR3 FAQ
What is IGF-1 LR3?
An IGF-1 analog modified to evade binding proteins, giving it far longer activity than native IGF-1. It is classed as IGF & growth factors.
Is IGF-1 LR3 FDA approved?
No. IGF-1 LR3 is not approved by the FDA for any indication. Material sold online is labelled for research use only.
Is IGF-1 LR3 legal in the US?
IGF-1 LR3 is not FDA approved and is not on FDA’s 503A bulks list. US compounding pharmacies cannot routinely prepare it.
What dose of IGF-1 LR3 is used in research?
Published research and practitioner protocols report 20-50 mcg, once daily, typically for 4 weeks. This is a reference range, not a recommendation; dosing should be set by a licensed clinician.
How is IGF-1 LR3 reconstituted?
A 1 mg vial mixed with 1 mL of bacteriostatic water gives 1.0 mg/mL. At that concentration 20 mcg is 2.0 units on a 100-unit insulin syringe.
What are the side effects of IGF-1 LR3?
Reported side effects include hypoglycaemia, injection-site swelling, headache, jaw pain. Contraindications: active or suspected malignancy, diabetes, pregnancy.
What is the half-life of IGF-1 LR3?
The reported half-life of IGF-1 LR3 is ~20-30 hours.
Is IGF-1 LR3 banned in sport?
Yes. IGF-1 LR3 falls under the World Anti-Doping Agency prohibited list.
References
Regulatory and primary sources
- FDA: Bulk drug substances that may present significant safety risks (Category 2 and withdrawn nominations) ↗ · content current as of April 22, 2026; checked October 18, 2026
- FDA: Bulk drug substances used in compounding under section 503A ↗ · how the 503A categories work
- WADA Prohibited List ↗ · current year
- FDA: Unapproved drugs and "research use only" products ↗ · regulatory status of non-approved products
- CAS Registry Number 946870-92-4 ↗ · chemical identity
Published literature
- Recombinant expression of IGF-1 and LR3 IGF-1 fused with xylanase in Pichia pastoris.Appl Microbiol Biotechnol 2023.PubMed 37261455 · doi:10.1007/s00253-023-12606-0
- IGF-1 has plaque-stabilizing effects in atherosclerosis by altering vascular smooth muscle cell phenotype.Am J Pathol 2011.PubMed 21281823 · doi:10.1016/j.ajpath.2010.10.007
- Novel insulin-like growth factor-methotrexate covalent conjugate inhibits tumor growth in vivo at lower dosage than methotrexate alone.Transl Res 2009.PubMed 19446281 · doi:10.1016/j.trsl.2009.02.005
- 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.PubMed 39610283 · doi:10.1177/13872877241299056
- The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration.Front Endocrinol (Lausanne) 2026.PubMed 42395176 · doi:10.3389/fendo.2026.1822475
- Involvement of insulin-like growth factor-1 and its binding proteins in proliferation and differentiation of murine bone marrow-derived macrophage precursors.Endocrine 1998.PubMed 9867252 · doi:10.1385/ENDO:9:2:185
Literature retrieved from PubMed on October 16, 2026, favouring human studies and reviews. Numbered markers in the text show which paper supports which statement; uncited entries are background reading.