Scientific context only. Not medical advice, not a recommendation to use.
At a glance
Synthetic analogue of insulin-like growth factor 1 (IGF-1) carrying an arginine substitution at position 3 and a 13-amino-acid N-terminal extension. These modifications lower binding to IGF-binding proteins and extend its duration of action relative to native IGF-1. LR3 IGF-1 is primarily an established cell-culture reagent (serum-free media, bioprocessing); it is NOT an approved human medicine. Use in the bodybuilding grey market is described; as an IGF-1 analogue, LR3 IGF-1 falls under the WADA anti-doping prohibition.
Researched for
Cell-culture supplement in serum-free mediaStimulation of cell proliferation and survival (in vitro)IGF-1 receptor pharmacology as a research tool
Official status
US: Unapproved
No FDA approval as a medicine. LR3 IGF-1 is sold as a laboratory chemical / cell-culture reagent ('not for human use'). As an IGF-1 analogue it is on the WADA prohibited list (category S2, prohibited at all times).
IGF-1 LR3 is a recombinantly produced variant of human IGF-1. Two changes define its properties: (1) at position 3, glutamic acid is replaced by arginine; (2) a 13-amino-acid sequence is added at the N-terminus ('Long'). Both modifications drastically reduce affinity for the six IGF-binding proteins (IGFBP-1 to -6) that normally bind native IGF-1 in the blood and regulate its availability at the receptor. As a result, a larger fraction of the molecule is freely available to bind the type-1 IGF receptor (IGF-1R) — the same receptor as native IGF-1. In preclinical models and cell culture, LR3 IGF-1 therefore acts as a more potent agonist than unmodified IGF-1. The downstream signalling pathway (PI3K/Akt and MAPK) is identical to that of IGF-1; the modification changes bioavailability, not the receptor target.
02
Evidence at a glance
Reading note. The distribution shows on which evidence tier each observation sits. Strong colours mark stronger evidence — weaker tiers are deliberately visible, not hidden.
4 observations · 3 tiers
Animal model
2
In vitro
1
Theoretical
1
03
What the studies show
Animal model
Ratte
Tomas FM, et al. 1996
Greater effect per molecule than native IGF-1 after injection in animal models, attributed to its low IGFBP binding
What does NOT follow: Animal finding. Superiority after injection was smaller than with continuous infusion; translation to humans is not established. No statement about human benefit or safety.
Animal model
Meerschweinchen
Conlon MA, et al. 1995
Promotion of organ growth in an animal model while simultaneously lowering circulating endogenous IGF-1, IGF-2 and IGFBP levels
What does NOT follow: Animal model. The paradoxical effect (growth despite falling endogenous IGF levels) reflects complex IGF-axis feedback — the long-term consequences of such a disturbance are not characterised. No human data.
In vitro
Zellkultur (CHO u. a.)
Prelle K, et al. 2001
Established use as a potent cell-culture supplement that enhances cell growth and protein yield in serum-free media (e.g. in CHO cell lines)
What does NOT follow: In-vitro use in industrial bioprocessing. This role as a laboratory reagent says nothing about the effect or safety of systemic use in humans.
Theoretical
—
Controlled human trials on the efficacy or safety of the LR3 analogue (muscle building, regeneration, clinical endpoints) are virtually absent
What does NOT follow: There are no published controlled human trials specifically on the LR3 analogue for sport or rehabilitation endpoints. Claims circulating in the grey market rely on animal/cell data and on IGF-1 biology in general, not on human studies of this substance.
04
Where studies disagree
Open question
Does the anabolic benefit of IGF-1 LR3 outweigh the theoretical cancer risk?
POSITION A
IGF-1 promotes muscle and tissue growth — the basis of the anabolic use expectation.
POSITION B
Elevated IGF-1 levels are epidemiologically associated with higher risk of several cancers; IGF-1 is strongly proliferative and anti-apoptotic.
CURRENT STATE · There are no controlled safety data on exogenous LR3 use in healthy people; the proliferative risk is real and unquantified.
05
Pharmacokinetics
Theoretical concentration curve at a half-life of 21 h. Pure pharmacokinetic model — not a dosing recommendation.
Risk notes for harm reduction — descriptive, not a usage or dosing guide.
⚠ Important — please read
This platform does NOT provide usage or dosing instructions. The points below describe risks and are meant to help avoid harm — they do not replace medical advice. Anyone who uses a substance should discuss it with a doctor.
There is no approved human use for this substance. What circulates online about amounts and frequency is self-experimentation without a safety net.
Online numbers are not a benchmark
Amounts from TikTok, YouTube and forums are mostly imitation rather than data — and are often wrongly derived from animal studies (µg/kg). Not a reliable benchmark for humans.
Sterility & infection risk
Injection solutions prepared or stored non-sterile carry an infection and abscess risk. Contamination is common with grey-market product.
Unknown product quality
Research-/grey-market product is not quality-tested: identity, purity and actual content are often unknown, and counterfeits occur.
Mind interactions
Combinations with medications or pre-existing conditions can carry risks (see the Interactions section). Clarify with a doctor beforehand.
Warning signs — seek medical help
With persistent pain, redness/swelling at the injection site, fever, shortness of breath, racing heart, chest pain or allergic reactions, seek medical help immediately.
A doctor, not a forum
Concrete questions about use and amount belong in a conversation with a doctor — not in a comment thread.
07
Known adverse events from studies
Factual reporting of what studies observed. Not a safety statement for individual use.
Theoretical
Human pharmacovigilance data practically non-existent
As no approved human use exists, there is no systematic safety profile. Strong, sustained activation of the IGF-1 receptor carries a theoretical mitogenic (cell-growth-promoting) risk; possible insulin-like effects (e.g. on blood glucose) are mechanistically plausible but not clinically characterised. No statement about actual frequency or severity.
07b
Interactions & combinations
Documented interactions and contraindications from studies, prescribing information and guidelines. Where no data exists, this is stated.
Reporting of risks, NOT a combination guide. The absence of an entry does not mean „safe to combine“ but „not sufficiently studied“.
No documented interactions recorded
We have not yet found robustly documented interactions for this peptide. This does NOT mean none exist — the data is limited.
08
Risks & hygiene aspects in the literature
What regulatory and scientific literature reports on risks, sterility and identity in non-pharmaceutical sources — descriptive, not a hygiene guide.
Identity and purity problem on the grey market
Grey-market products sold as 'IGF-1 LR3' are not standardised. Without analytical testing (e.g. mass spectrometry), neither identity nor purity nor actual content can be verified; confusion with IGF-1, MGF or mixtures has been documented.
09
Regulatory voices
Direct statements from official assessment documents — paraphrased with date and source link.
WADAWorld Anti-Doping Agency
2026
Classification of IGF-1 and its analogues on the anti-doping prohibited list
All forms of exogenous IGF-1 are prohibited at all times, and any substance containing any form of exogenous IGF-1 should be considered prohibited.
Reading note. This section gathers popular claims from communities and forums. They are explicitly marked as weakest-tier evidence. Unblinded self-reports are particularly prone to placebo, recall and confirmation biases.
Why no amounts or protocols are listed here. We deliberately show only WHAT communities report — not in what amount or how it is used. Anecdotal "doses" or "biohacker protocols" are neither verified nor standardised nor safe; publishing them would be a usage guide, which we do not provide on principle. Specific amounts belong in a conversation with a doctor, not in a forum.
In bodybuilding forums IGF-1 LR3 is described as a 'longer-acting' and 'more potent' growth factor compared with native IGF-1 or MGF.
common, often compared with MGF and IGF-1
Not supported by studies: These claims improperly extrapolate animal/cell findings to humans. There are no controlled human trials on the efficacy or safety of the LR3 analogue for muscular endpoints. 'More potent in vitro' does not mean 'useful or safe in humans'.
11
Legal status by country
Country
Status
Note
Checked
United States
Unapproved
No FDA approval as a medicine. LR3 IGF-1 is sold as a laboratory chemical / cell-culture reagent ('not for human use'). As an IGF-1 analogue it is on the WADA prohibited list (category S2, prohibited at all times).
2026-06-07
Germany
Unapproved
No EMA/BfArM approval as a medicine. Sale as a 'research chemical' does not cover human use. As an IGF-1 analogue, WADA-prohibited (category S2, at all times). The legal framework for purchase and possession should be assessed case by case (German Medicines Act).
2026-06-07
12
Reconstitution calculator
Pure mg/mL maths — works like a calculator. Not a usage recommendation.
Peptides ship as a dry powder. Once dissolved in a liquid (reconstitution), this calculator answers a single question: how much substance is in one millilitre of solution afterwards?
1Enter the vial's substance amount (printed on the label).
2Enter how much solvent you add.
3Result = concentration in mg per mL.
Printed on the label
/
Liquid you add
=
2.50
mg / mL
5 mg in 2 mL gives 2.50 mg/mL — each millilitre contains 2.50 mg of substance.
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
Insulin-like growth factor I (IGF-I) and long R(3)IGF-I differently affect development and messenger ribonucleic acid abundance for IGF-binding proteins and type I IGF receptors in in vitro produced bovine embryos