IGF-1 LR3
updated
IGF-1 LR3 is an IGF-1 analogue, first made as a cell-culture reagent, whose added 13-amino-acid tail and position-3 swap let it escape binding proteins that restrain natural IGF-1. Bodybuilders use it for muscle growth, sometimes calling it safer than other IGF-1 forms. Animal studies show growth and metabolic effects, but no study has given it to people, and its potent signaling raises concerns about low blood sugar, tissue overgrowth and tumor biology. Graded F for potent growth-factor biology with no human record; mecasermin, the approved IGF-1 drug, is a different molecule.
long R3 insulin-like growth factor I analogue
- 13-residue N-terminal extension MFPAMPLSSLFVN
- Arg replaces Glu at native IGF-1 position 3
- Reduced IGF-binding-protein interaction in vitro
- No registered human trial in the cited records
How is IGF-1 LR3 different from native IGF-1?
It adds MFPAMPLSSLFVN to the N-terminus and replaces native Glu3 with Arg. Those changes reduce binding-protein interaction and alter potency and exposure. It is not mecasermin or ordinary recombinant IGF-1.
Correct folding and three disulfide bonds are part of the active identity. Purity percentage or nominal mass alone cannot show the right conformation and potency.
source: Primary paper · modified analogue in cells, Francis GL et al. Journal of Molecular Endocrinology, 1992.
source: Protein chemistry · disulfide folding, Milner SJ et al. Biotechnology and Bioengineering, 1998.
Has IGF-1 LR3 built muscle or improved recovery in people?
The cited records include no direct administered-human trial. Cell potency, animal growth studies, and clinical experience with native recombinant IGF-1 do not establish efficacy, pharmacokinetics, or safety for LR3.
Can mecasermin’s label be used for LR3?
No. Mecasermin is recombinant human IGF-1. LR3 has 14 sequence changes or additions designed to alter binding-protein control, so exposure and risk cannot be assumed equivalent.
source: PubMed and registry · no direct human trial, PubMed and ClinicalTrials.gov records for IGF-1 LR3, Long R3 IGF-I, Long R3 IGF-1, and LR3.
source: Primary paper · modified analogue in cells
source: Animal study · growth and nitrogen effects, Experimental IGF-I analogue research.
What does LR3 do in experiments?
LR3 can be more potent than native IGF-1 in cell systems that secrete IGF-binding proteins, while being less potent in systems without them. Animal studies show growth and metabolic activity. The cited experiments do not support a universal multiplier such as ‘three times stronger.’
source: Primary paper · modified analogue in cells
source: Animal study · growth and nitrogen effects
source: Animal study · analogue exposure, Experimental IGF-I analogue research.
What is known about IGF-1 LR3 side effects, and what are the main safety concerns?
The cited records provide no direct human rates. Potent IGF-receptor signaling raises plausible concerns about hypoglycemia, edema, intracranial pressure, tissue overgrowth, cardiac effects, and tumor biology, but exact LR3 risks and frequencies cannot be quantified from native IGF-1 labels or epidemiology.
- Glucose: direct LR3 dose-response and interaction data with insulin or glucose-lowering drugs are absent.
- Growth signaling: endogenous IGF-1 associations do not quantify cancer risk from LR3 exposure.
- Product quality: sequence, fold, aggregates, endotoxin, sterility, concentration, and bioactivity all need product-specific control.
Is IGF-1 LR3 FDA approved?
The cited FDA and clinical records include no approved IGF-1 LR3 drug, prescribing label, or registered human trial. WADA prohibits IGF-1 analogues for covered athletes.
source: PubMed and registry · no direct human trial
source: WADA 2026 · IGF-1 and analogues, World Anti-Doping Agency, effective 1 January 2026.
Studies and sources
Primary paper · modified analogue in cells
Protein-engineering and cell study
Francis GL et al. Journal of Molecular Endocrinology, 1992.
Long R3 IGF-I was engineered with a 13-amino-acid N-terminal extension and Arg replacing Glu at native position 3. It was more potent than IGF-I in cells that secreted IGF-binding proteins, but less potent in cells without them. The work was in vitro and did not administer the analogue to people.
- Participants / model
- Cultured cell systems with different IGF-binding-protein conditions
- Treatment
- Long R3 IGF-I and native IGF-I
- Study design
- Protein-engineering and comparative cell-bioactivity study
Protein chemistry · disulfide folding
Protein chemistry study
Milner SJ et al. Biotechnology and Bioengineering, 1998.
The study examined production and disulfide folding of recombinant Long R3 IGF-I. It supports the importance of manufacturing and conformational control but supplies no human efficacy or safety result.
- Participants / model
- Recombinant production and analytical systems
- Treatment
- Long R3 IGF-I folding and purification
- Study design
- Protein-process study
Animal study · growth and nitrogen effects
Animal study
Experimental IGF-I analogue research.
Long R3 IGF-I altered growth or nitrogen-related measures in an animal model. Species exposure and growth readouts do not establish human muscle benefit or safety.
- Participants / model
- Experimental animals
- Treatment
- Long R3 IGF-I
- Study design
- Controlled animal study
Animal study · analogue exposure
Animal study
Experimental IGF-I analogue research.
The analogue was administered in an animal metabolic or growth experiment. The result does not supply a human dose, glucose-risk estimate, or clinical outcome.
- Participants / model
- Experimental animals
- Treatment
- Long R3 IGF-I
- Study design
- Controlled animal study
PubMed and registry · no direct human trial
PubMed and ClinicalTrials.gov records
PubMed and ClinicalTrials.gov records for IGF-1 LR3, Long R3 IGF-I, Long R3 IGF-1, and LR3.
The cited records include no relevant registered human intervention trial or administered-human publication for IGF-1 LR3, Long R3 IGF-I, Long R3 IGF-1, LR3, or the extension sequence.
Read the original sourceWADA 2026 · IGF-1 and analogues
Sports rule
World Anti-Doping Agency, effective 1 January 2026.
IGF-1 and its analogues are prohibited under S2 for athletes covered by the Code.
- Study design
- Binding sport rule for covered athletes
Why is IGF-1 LR3 in F tier?
F reflects potent growth-factor biology without a direct human product record. Mecasermin and native IGF-1 use different molecules and cannot supply LR3 pharmacokinetics, efficacy, or safety.
how tiers are graded: methodology · every cited source · about reptides.
Research reference, not medical advice. Entries distinguish product labels, study doses and reported protocols. Check the linked source for the product, route and population.