MK-677 (Ibutamoren) vs Tesamorelin
MK-677 (Ibutamoren) (Orally active non-peptide growth-hormone secretagogue (ghrelin-receptor agonist)) and Tesamorelin (GHRH analog (stabilized long-acting GHRH(1-44) analog)) 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 | MK-677 (Ibutamoren) | Tesamorelin |
|---|---|---|
| Compound class | Orally active non-peptide growth-hormone secretagogue (ghrelin-receptor agonist) | GHRH analog (stabilized long-acting GHRH(1-44) analog) |
| Research category | Growth & GH-Axis | Growth & GH-Axis |
| Length (amino acids) | Not documented | 44 amino acids |
| Molecular weight | 624.8 g/mol (free base); approximately 936.2 g/mol as the mesylate salt | Approximately 5136 g/mol |
| Half-life | Approximately 24 hours (supports once-daily dosing in studies) | Short in circulation (reported approximately 26-38 minutes) despite chronic dosing effects |
| Origin | 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. | Tesamorelin is a synthetic analog of human growth-hormone-releasing hormone (GHRH 1-44) with an N-terminal trans-3-hexenoyl modification that improves stability. It is marketed as Egrifta. |
“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 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.
How Tesamorelin works
Tesamorelin is an agonist of the GHRH receptor on anterior-pituitary somatotrophs, stimulating endogenous GH secretion and raising IGF-1. The N-terminal hexenoyl group protects it from rapid DPP-4 degradation, improving stability relative to native GHRH. By acting upstream, it stimulates physiologic GH release subject to normal feedback.
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.
MK-677 (Ibutamoren)
Tesamorelin
What sets each apart
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.
Tesamorelin
Tesamorelin is a stabilized GHRH(1-44) analog and, uniquely in this set, an FDA-approved medicine, distinguishing it from research-only GHRH analogs like sermorelin and CJC-1295.
Frequently asked questions
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.
What is tesamorelin?
Tesamorelin is a synthetic stabilized analog of the full 44-amino-acid human growth hormone-releasing hormone (GHRH). A trans-3-hexenoic acid group is attached to the N-terminus to resist enzymatic degradation, and it acts on the GHRH receptor to stimulate endogenous GH secretion.
Is tesamorelin an FDA-approved drug?
Yes. Tesamorelin (brand name Egrifta) is FDA-approved for the reduction of excess abdominal fat in HIV-infected patients with lipodystrophy. It is one of the few GHRH analogs to reach full FDA approval; an updated F8/WR formulation was approved in 2025.
How does tesamorelin differ from sermorelin and CJC-1295?
Sermorelin and CJC-1295 are based on the shorter GHRH(1-29) fragment, whereas tesamorelin is a stabilized analog of the full 44-amino-acid GHRH. Its N-terminal modification gives it greater stability than sermorelin while remaining a short-acting daily-dosed GHRH analog.
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.