MK-677 (Ibutamoren)

MK-677 is a non-peptide agonist of the growth hormone secretagogue receptor (GHSR1a), the same receptor activated by the endogenous hormone ghrelin. By activating GHSR1a on somatotroph cells in the anterior pituitary, MK-677 stimulates GH release in a pulsatile fashion that mimics physiological GH secretion. It also increases GH release by reducing somatostatin tone at the hypothalamic level. MK-677 has a plasma half-life of approximately 6 hours, with IGF-1 elevation sustained over 24 hours with daily dosing. Unlike exogenous GH, MK-677 preserves the normal feedback mechanisms of the GH axis. As a ghrelin mimetic, it also activates appetite pathways in the arcuate nucleus and vagal afferents, explaining the increased hunger commonly observed.

Nass et al. (2008) conducted a 2-year RCT in 65 healthy elderly adults showing MK-677 (25 mg/day) restored GH and IGF-1 to young-adult levels. Fat-free mass increased by approximately 1.1 kg but functional outcomes were not measured. Fasting glucose increased significantly and some subjects developed impaired glucose tolerance. Murphy et al. (1998) showed MK-677 reversed nitrogen wasting during caloric restriction in young men over 7 days. Bach et al. (2004) studied MK-677 in elderly hip fracture patients and found increased IGF-1 but failed to meet the primary composite functional endpoint. No Phase 3 efficacy trials have been completed. The consistent finding of worsened insulin sensitivity has limited clinical development.

MK-677 was developed by Merck but never received FDA approval. Clinical development did not advance beyond Phase 2. It is classified as an investigational compound. MK-677 is prohibited in sport by WADA under the category of GH secretagogues. It is widely available in grey-market online stores as a research chemical, often sold in capsule or liquid form. These products are not manufactured under GMP conditions and quality varies significantly.

Fasting glucose and HbA1c should be assessed at baseline and monitored regularly (every 3 to 6 months), especially in patients with metabolic risk factors. IGF-1 levels can confirm GH axis activation and guide dosing. Monitor for peripheral edema, weight changes, and appetite effects. Assess body composition if that is the treatment goal. Consider screening for occult malignancy before long-term use given sustained IGF-1 elevation.

These are general considerations for clinical awareness and do not constitute prescriptive monitoring recommendations for any individual patient.

MK-677 is a non-peptide small molecule with relatively good chemical stability compared to peptide secretagogues. Grey-market products are typically sold as capsules or oral solutions. Store at controlled room temperature (20 to 25 degrees C) in a dry location protected from light. No reconstitution is required for oral formulations. Formal pharmaceutical stability data are proprietary to Merck.

1. 1

   RCT

   Two-Year Effects of Oral MK-677 on GH, IGF-I, Body Composition, and Fat-Free Mass in Healthy Elderly Adults

   Nass R, Pezzoli SS, Oliveri MC, et al. (2008). Journal of Clinical Endocrinology & Metabolism

   Key findings: MK-677 increased GH and IGF-1 levels to those of young adults over 2 years. FFM increased by approximately 1.1 kg. Fasting glucose increased and insulin sensitivity declined.

   Limitations: Small sample (n=65). No functional outcomes measured. Concerning metabolic effects.

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2. 2

   RCT

   MK-677, an Oral Growth Hormone Secretagogue, Reverses Diet-Induced Catabolism

   Murphy MG, Plunkett LM, Gertz BJ, et al. (1998). Journal of Clinical Endocrinology & Metabolism

   Key findings: MK-677 reversed nitrogen wasting during caloric restriction, suggesting potential for combating catabolic states. GH and IGF-1 levels increased dose-dependently.

   Limitations: Short-duration study (7 days). Healthy young men on caloric restriction, not clinical catabolic patients.

3. 3

   RCT

   Oral Administration of MK-677 in Hip Fracture Patients

   Bach MA, Hansen TK, Frick G, et al. (2004). Journal of Clinical Endocrinology & Metabolism

   Key findings: MK-677 increased IGF-1 and improved functional performance in some measures in elderly hip fracture patients, but did not significantly improve the primary composite endpoint.

   Limitations: Failed primary endpoint. Modest sample size. Heterogeneous patient population.

4. 4

   review

   Growth Hormone Secretagogues: Mechanism of Action and Use in Aging

   Nass R, Thorner MO. (2002). Growth Hormone & IGF Research

   Key findings: Review of GH secretagogue pharmacology including MK-677. Discusses ghrelin receptor (GHSR) agonism, effects on GH pulsatility, and potential applications in age-related GH decline.

   Limitations: Narrative review. Authored prior to completion of long-term clinical trials.