Comparison
GHRP-6 vs. IGF-1 LR3
Two peptides side-by-side — identity, evidence base, legal status and known adverse events.
Identity
Category
Growth
Growth
CAS no.
87616-84-0
143045-27-6
Molecular weight
873.02 g/mol
9117.6 g/mol
Half-life
0.4 h
21 h
Sequence
His-D-Trp-Ala-Trp-D-Phe-Lys-NH2MFPAMPLSSLFVNGPRTLCGAELVDALQFVCGDRGFYFNKPTGYGSSSRRAPQTGIVDECCFRSCDLRRLEMYCAPLKPAKSAMechanism of action
GHRP-6
GHRP-6 is a high-affinity agonist of the growth-hormone secretagogue receptor 1a (GHSR-1a) — the same receptor later shown to bind the endogenous hormone ghrelin. The identification of GHRP-6 as a pharmacological anchor led to cloning of GHSR in 1996 and the discovery of ghrelin itself in 1999. GHRP-6 stimulates pituitary GH secretion via a pathway independent of GHRH and can be combined synergistically with GHRH. Via GHSR in the hypothalamus it additionally activates NPY/AgRP neurons, producing an orexigenic (appetite-stimulating) effect in animal models.
IGF-1 LR3
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.
Evidence base
Highest evidence
Human trial
Animal model
Studies
4
4
of which in humans
2
0
Effects recorded
4
4
Open conflicts
1
1
Documented adverse events
2
1
Legal status
Full entries
Frequently asked questions
- What is the difference between GHRP-6 and IGF-1 LR3?
- GHRP-6 is classified as "Growth", while IGF-1 LR3 is classified as "Growth". GHRP-6: Synthetic hexapeptide that founded the class of growth-hormone-releasing peptides (GHRPs). Cyril Bowers identified GHRP-6 in the late 1970s as the first orally and parenterally active GH secretagogue with no structural similarity to GHRH. Never approved as a medicine; downstream analogs (GHRP-2, hexarelin, ipamorelin) were pursued clinically. IGF-1 LR3: 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. This page contrasts both neutrally and source-based — with no usage or dosing recommendation.
- Which peptide is better supported by science, GHRP-6 or IGF-1 LR3?
- The highest available evidence level is "Human trial" for GHRP-6 and "Animal model" for IGF-1 LR3. A higher evidence level means more robust data, but says nothing about suitability for an individual. The full body of evidence is on each peptide's own page.
- What is the legal status of GHRP-6 and IGF-1 LR3 in Germany and the United States?
- Germany: GHRP-6 — Unapproved, IGF-1 LR3 — Unapproved. United States: GHRP-6 — Unapproved, IGF-1 LR3 — Unapproved. These are factual summaries with source and review date on the individual pages.