Comparison · Growth-hormone secretagogues
Ipamorelin vs MK-677
Both stimulate growth-hormone release via the ghrelin receptor, but the similarity ends there. Here's how Ipamorelin (peptide, injectable, short half-life) and MK-677 (oral, ~24 h half-life) actually differ in research.
At a glance
| Attribute | Ipamorelin | MK-677 |
|---|---|---|
| Class | Pentapeptide | Oral small molecule |
| Target | GHSR-1a | GHSR-1a |
| Half-life | ~2 hours | ~24 hours |
| Route | Subcut. injection (research) | Oral |
| Cortisol / prolactin | Minimal | Some appetite / water retention |
Mechanism
Both compounds bind the ghrelin receptor (GHSR-1a) on somatotrophs in the anterior pituitary, triggering a pulsatile growth-hormone release. Ipamorelin is selective and short-acting; MK-677 produces a sustained, day-long elevation of GH and IGF-1 in published studies.
Half-life & dosing pattern
Ipamorelin's ~2-hour half-life makes it suited to multiple daily doses or once-nightly use timed to natural GH pulses. MK-677's ~24-hour half-life enables once-daily oral dosing.
Research applications
Ipamorelin is favoured in research where investigators want a clean, ghrelin-receptor-selective probe without confounding cortisol or prolactin movement. MK-677 is favoured where chronic, steady IGF-1 elevation is the variable under study.
Side-effect signal in literature
Ipamorelin shows minimal cortisol/prolactin effects in published research. MK-677 has documented appetite stimulation (via ghrelin pathway), mild water retention and possible insulin sensitivity shifts in longer-term studies.
Frequently asked questions
Are Ipamorelin and MK-677 the same class?+
Both are growth-hormone secretagogues acting on the ghrelin receptor (GHSR-1a), but Ipamorelin is a peptide and MK-677 is an oral small molecule with very different pharmacokinetics.
Which has the longer half-life?+
MK-677 has a half-life of ~24 hours allowing once-daily dosing in studies; Ipamorelin is ~2 hours and is typically dosed multiple times per day in research protocols.
Does either raise cortisol or prolactin?+
Ipamorelin is notable for minimal effects on cortisol and prolactin in published research; MK-677 has shown some appetite and water-retention effects via ghrelin signalling.
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