Description
MK-677 (Ibutamoren, Ibutamoren Mesylate) is an oral ghrelin receptor agonist and growth hormone secretagogue. Despite being listed in the SARM category, MK-677 doesn’t act structurally or mechanistically via the androgen receptor; it activates the GHS receptor (ghrelin receptor) in the hypothalamus and pituitary.
Per study reports MK-677 stimulates pulsatile growth hormone secretion via the physiologic pathway. Unlike exogenous GH (rhGH), MK-677 preserves the natural negative feedback loop via IGF-1, preventing overstimulation. Studies show that older adults under MK-677 reach GH pulse amplitudes typical of young adults.
Pharmacokinetics are excellent: orally available with a 4-6 hour half-life. A once-daily dose suffices to elevate IGF-1 levels over 24h. Compared to GHRPs (peptide secretagogues like Ipamorelin), MK-677 is substantially more practical (oral vs subcutaneous).
In the landmark Nass 2008 study (Annals of Internal Medicine), MK-677 increased fat-free mass in older adults by 1.6 kg vs placebo over two years. Known effects in studies include increased appetite (ghrelin action), mild fluid retention and slight increase in fasting glucose (about 5 mg/dL).
You can order MK-677 as oral tablets in one bottle with 10mg or 25mg per tablet.
This information is for research and educational purposes only. No medical recommendations.
Risks & Safety
MK-677 sits in the mid range of the risk scale. As a ghrelin receptor agonist the compound acts via a physiologic pathway, but several accompanying effects are consistently documented in the studies.
Documented in studies and the literature:
- Appetite increase: as a direct ghrelin action, a markedly increased appetite is the most commonly documented effect.
- Water retention: mild fluid retention is described in the studies, especially at the start of use.
- Blood sugar: a slight rise in fasting glucose is documented, relevant in pre-existing insulin resistance research.
- Prolactin: a possible rise in prolactin levels is described in the literature.
- No HPG suppression: unlike true SARMs, MK-677 does not suppress the HPG axis.
Monitoring via bloodwork is recommended. This classification does not replace medical advice. Risk and responsibility for any actual use lie entirely with the buyer.
Studies
- Effects of an Oral Ghrelin Mimetic on Body Composition and Clinical Outcomes in Healthy Older Adults - Annals of Internal Medicine 2008, Nass et al: Two-year RCT on MK-677, gold-standard body composition study in healthy older adults.
- Stimulation of the growth hormone (GH)-insulin-like growth factor I axis by daily oral administration of a GH secretogogue (MK-677) in healthy elderly subjects - The Journal of Clinical Endocrinology & Metabolism 1996, Chapman et al: Daily oral MK-677 raises IGF-1 in elderly subjects into the range of young adults.
- MK-677, an Orally Active Growth Hormone Secretagogue, Reverses Diet-Induced Catabolism - The Journal of Clinical Endocrinology & Metabolism 1998, Murphy et al: MK-677 improves nitrogen balance under caloric restriction.
- Structural basis of human ghrelin receptor signaling by ghrelin and the synthetic agonist ibutamoren - Nature Communications 2021, Liu et al: Cryo-EM structures of the ghrelin receptor bound to Ibutamoren.
- LGD-4033 and MK-677 use impacts body composition, circulating biomarkers, and skeletal muscle androgenic hormone and receptor content: A case report - Experimental Physiology 2022, Cardaci et al: Case report on biomarker and body composition changes under MK-677.
