Source comparison
Ghrelin Receptor MK-677 GHRP Activation vs Peptide GHRPs
Receptor Affinity 0.7 nM at GHS-R1a 0.2 nM at GHS-R1a 0.5 nM at GHS-R1a Peptide GHRPs bind slightly tighter, but practical difference is negligible at therapeutic doses Oral Bioavailability 60–65% <1% (requires injection) MK-677's small-molecule structure surv
This comparison does not assign a generated winner or score.
- Receptor Affinity
- 0.7 nM at GHS-R1a
- 0.2 nM at GHS-R1a
- 0.5 nM at GHS-R1a
- Peptide GHRPs bind slightly tighter, but practical difference is negligible at therapeutic doses
- Oral Bioavailability
- 60–65%
- <1% (requires injection)
- MK-677's small-molecule structure survives gastric acid. Peptides degrade before absorption
- Half-Life
- 4–6 hours
- 20–30 minutes
- 60–90 minutes
- Extended half-life allows once-daily dosing; peptides require multiple daily injections
- Receptor Desensitization
- Minimal after 6 months
- Moderate after 4–6 weeks
- Severe after 2–4 weeks
- MK-677 maintains efficacy long-term; peptide GHRPs lose potency with continuous use
- Appetite Stimulation
- Significant (+++/5)
- Moderate (++/5)
- Very Significant (++++/5)
- Minimal (+/5)
- All GHS-R1a agonists trigger appetite, but GHRP-6 and MK-677 are most pronounced
- IGF-1 Elevation
- +40–60% at 25mg
- +30–50% at 100mcg
- +35–55% at 100mcg
- MK-677 produces more sustained IGF-1 elevation due to prolonged GH secretion window
- The bottom line: MK-677 is the only orally active ghrelin receptor agonist with clinically meaningful bioavailability. Peptide GHRPs require injection and face rapid tolerance development, while MK-677 maintains efficacy across months of continuous use. For research protocols requiring sustained growth hormone elevation without daily injections, ghrelin receptor MK-677 GHRP activation is the most practical pathway.