MK-677

Overview

MK-677 (ibutamoren) is an orally active, non-peptide growth hormone secretagogue that mimics ghrelin's action. Despite not being a peptide, it is commonly tracked alongside GH-releasing peptides due to its similar mechanism and use case. It elevates GH and IGF-1 levels without affecting cortisol.

Mechanism of Action

MK-677 activates the ghrelin receptor (GHS-R1a) in the pituitary and hypothalamus, stimulating GH release. Unlike GHRPs, it is orally bioavailable with a long half-life (~24 hours). It increases GH pulsatility and elevates IGF-1 levels persistently. It does not significantly increase cortisol or prolactin.

Research Summary

Multiple clinical trials in elderly and GH-deficient populations demonstrate sustained increases in GH and IGF-1, improvements in body composition, increased bone density, and improved sleep quality. A 2-year trial showed sustained IGF-1 elevation without tachyphylaxis. Not FDA-approved despite extensive human data.

Dosing Information

Reported Side Effects

• Increased appetite
• Water retention and bloating
• Drowsiness and lethargy
• Elevated fasting glucose
• Tingling or numbness in extremities
• Joint stiffness

Research References

• MK-677, an oral growth hormone secretagogue, reverses diet-induced catabolism (1998)
• Two-year effects of ibutamoren mesylate on growth hormone, IGF-I, body composition, and bone density (2008)
• Oral administration of growth hormone secretagogue MK-677 increases growth hormone and IGF-I in obese subjects (2001)