IGF-1 LR3[Long R3 insulin-like growth factor 1]
Compound snapshot
Class
Research peptide
FDA approved
No
Clinical development
Phase 2
Last reviewed
September 2026
Research areas
Growth hormone axis / Body composition / Recovery
Regulatory status
Research use only — not approved
Internet attention
Moderate
Registry query
IGF-1 LR3
An engineered 83-amino-acid analogue of human IGF-1 with an N-terminal extension and an amino-acid substitution designed to reduce binding to IGF-binding proteins. It is not the approved prescription drug mecasermin.
Reality check — what we actually know
Supported by human evidence
- No adequately powered randomised human trials establish the outcomes this compound is marketed for.
Animal research only
- Useful as a laboratory reagent for studying IGF-1 receptor signalling without as much binding-protein interference
- Promotes anabolic and cell-growth signals in cultured cells and animal models
- Bodybuilding claims about muscle growth are extrapolated from preclinical biology, not controlled human trials
Mechanistically plausible
- Activates the IGF-1 receptor and downstream PI3K-Akt-mTOR and MAP-kinase pathways involved in cell survival, protein synthesis and growth. Reduced binding-protein affinity may leave more active compound available than with native IGF-1.
Common internet claims
- Online discussion frequently presents IGF-1 LR3 as a proven treatment rather than a research compound.
Not established
- Human efficacy for the outcomes commonly claimed
- Optimal route, quantity and duration in humans
- Long-term human safety
Evidence distribution
Each band is a live PubMed search for IGF-1 LR3, filtered to that kind of study. Top is the strongest evidence; the base is reasoning, not proof. A band with no records means that kind of study has not been published for this compound yet.
Mechanism and reported findings
Activates the IGF-1 receptor and downstream PI3K-Akt-mTOR and MAP-kinase pathways involved in cell survival, protein synthesis and growth. Reduced binding-protein affinity may leave more active compound available than with native IGF-1.
- Useful as a laboratory reagent for studying IGF-1 receptor signalling without as much binding-protein interference
- Promotes anabolic and cell-growth signals in cultured cells and animal models
- Bodybuilding claims about muscle growth are extrapolated from preclinical biology, not controlled human trials
Strength of the evidence: Preclinical and laboratory evidence only. No completed controlled human trials establish the safety or effectiveness of IGF-1 LR3. Mecasermin has human evidence for a narrow paediatric deficiency indication, but those results cannot be transferred to LR3.
Safety and known cautions
Can plausibly cause dangerous low blood sugar and stimulate growth in existing tumours or abnormal tissues. Long duration and unregulated purity add uncertainty. It is prohibited in sport and is not a substitute for medically prescribed mecasermin.
Evidence at a glance
No single score, on purpose. The line beside each bar shows how much reported outcomes vary between studies.
Development stage
- Discovery
- Preclinical
- Phase 1
- Phase 2Current
- Phase 3
- Regulatory review
- Approved