IGF-1 LR3 vs MK-677 (Ibutamoren)
IGF-1 LR3 (IGF-1 analog (Long R3 IGF-1 variant)) and MK-677 (Ibutamoren) (Orally active non-peptide growth-hormone secretagogue (ghrelin-receptor agonist)) are documented as co-studied in the PeptiDex library. This page puts the two entries side by side on class, molecular weight, half-life, origin, mechanism and studied research areas — every value taken from the entry it belongs to.
Why these two are co-studied
Cross-referenced for research context — not a usage or combination recommendation.
At a glance
| Attribute | IGF-1 LR3 | MK-677 (Ibutamoren) |
|---|---|---|
| Compound class | IGF-1 analog (Long R3 IGF-1 variant) | Orally active non-peptide growth-hormone secretagogue (ghrelin-receptor agonist) |
| Research category | Growth & GH-Axis | Growth & GH-Axis |
| Length (amino acids) | 83 amino acids | Not documented |
| Molecular weight | Approximately 9111 g/mol | 624.8 g/mol (free base); approximately 936.2 g/mol as the mesylate salt |
| Half-life | Substantially longer than native IGF-1; reported on the order of many hours (approximately 20-30 hours) due to reduced IGFBP binding | Approximately 24 hours (supports once-daily dosing in studies) |
| Origin | IGF-1 LR3 (Long R3 IGF-1) is a synthetic analog of insulin-like growth factor 1 with an arginine substituted for glutamate at position 3 and a 13-amino-acid N-terminal extension, giving an 83-residue peptide. It was originally developed for cell-culture applications. | MK-677 (Ibutamoren, development code MK-0677) is an orally active, non-peptide growth-hormone secretagogue developed by Merck. It is a spiroindane/spiropiperidine small molecule, not a peptide. |
“Not documented” means the PeptiDex entry records no value for that field. Nothing on this page is estimated, and no figure is carried over from one compound to the other.
How IGF-1 LR3 works
IGF-1 LR3 is an agonist of the IGF-1 receptor, driving the same anabolic and proliferative signaling as native IGF-1. The Arg3 substitution and N-terminal extension sharply reduce its affinity for IGF-binding proteins (IGFBPs), leaving more peptide free and biologically active and greatly extending its functional half-life relative to native IGF-1.
How MK-677 (Ibutamoren) works
MK-677 is an agonist of the growth-hormone secretagogue receptor (GHS-R1a, the ghrelin receptor), mimicking ghrelin to stimulate pulsatile GH release from the pituitary and raise circulating IGF-1. Unlike the peptide GHRPs, it is orally bioavailable and long-acting. It can also modestly increase cortisol and appetite via ghrelin-receptor signaling.
Mechanistic descriptions reflect published research-literature understanding and are quoted from each compound's own entry. Much peptide research is preclinical (in-vitro or animal-model); mechanism in humans may differ and is not established for many compounds.
Where each one appears in the literature
The research contexts each entry documents. Listing a research area is not a claim of efficacy or a therapeutic indication, and the two lists are not scored against each other.
IGF-1 LR3
MK-677 (Ibutamoren)
What sets each apart
IGF-1 LR3
IGF-1 LR3 is engineered for a long half-life via Arg3 substitution and an N-terminal extension that minimize IGFBP binding, contrasting with the short-acting, truncated IGF-1 DES.
MK-677 (Ibutamoren)
Unlike the peptide secretagogues in this class, MK-677 is a non-peptide, orally active, long-acting ghrelin-receptor agonist, making its route and pharmacokinetics fundamentally different.
Frequently asked questions
What is IGF-1 LR3?
IGF-1 LR3 (Long R3 IGF-1) is an 83-amino-acid analog of insulin-like growth factor-1 with an arginine substituted at position 3 and a 13-amino-acid N-terminal extension. It is an IGF-1 receptor agonist engineered for very low IGF-binding-protein affinity and greatly extended stability.
How does IGF-1 LR3 differ from IGF-1 DES?
Both reduce IGFBP binding, but IGF-1 LR3's modifications give it a long half-life (~20-30 hours) versus IGF-1 DES's ~20-30 minutes. LR3 is studied for sustained systemic IGF-1 receptor activation, whereas DES is studied for short, localized action.
Why does IGF-1 LR3 have such an extended half-life?
The Arg3 substitution plus the N-terminal extension sharply lower its affinity for IGF-binding proteins while improving metabolic stability, so the peptide circulates far longer than native IGF-1. The research literature reports it is roughly three times more potent than native IGF-1.
What is MK-677 (ibutamoren)?
MK-677 (ibutamoren) is an orally active, non-peptide growth hormone secretagogue that mimics ghrelin and binds the GHS-R1a receptor. Because it is a small molecule rather than a peptide, it survives digestion and is studied as an oral agent that raises GH and IGF-1 levels.
How does MK-677 differ from injectable GHRPs like ipamorelin?
MK-677 targets the same ghrelin receptor as injectable GHRPs but is a non-peptide small molecule with ~60-70% oral bioavailability, so it is taken by mouth rather than injected. Its long half-life sustains elevated IGF-1 across the day, unlike the discrete pulses from short-acting injectable GHRPs.
What does MK-677's long half-life imply for research?
MK-677 has a long biological half-life (reported ~24 hours of sustained IGF-1 elevation), which supports once-daily oral dosing in research protocols and produces a sustained elevation of GH/IGF-1 rather than a sharp pulse.
Answers are the ones published on each compound's own PeptiDex entry. They are educational summaries of research-literature context and are not medical advice.