MK-677 (Ibutamoren): Research, Results & Side Effects

MK-677 (ibutamoren mesylate) is an orally active, small-molecule growth hormone secretagogue that mimics ghrelin at the growth hormone secretagogue receptor; it is not a peptide. Randomized human trials from the 1990s and 2000s show it reliably raises growth hormone and IGF-1 and increases fat-free mass, but those biochemical gains did not translate into better strength, function, or slower Alzheimer's progression. Its side effects include increased appetite, fluid retention, higher fasting glucose with reduced insulin sensitivity, and a heart-failure signal that stopped a hip-fracture trial early. It is not FDA-approved.

Educational content for licensed healthcare professionals. Not medical advice; dosing and treatment decisions belong to the prescribing clinician.

MK-677 at a Glance

What Is MK-677?

MK-677, also called MK-0677 or ibutamoren mesylate, was developed by Merck in the 1990s as an orally active compound that triggers pulsatile growth hormone release. It acts on the receptor that Merck scientists cloned in 1996 from pituitary and hypothalamus, the growth hormone secretagogue receptor [1]. Ghrelin, the stomach hormone later identified as that receptor's natural ligand, is why MK-677 is often called a "ghrelin mimetic" [2].

It is important to be accurate about chemistry: MK-677 is a small molecule, not a peptide. It is often sold alongside peptides and grouped with peptide secretagogues such as ipamorelin, but its oral bioavailability and long duration of action come from being a non-peptide drug. Its closest peptide counterpart is ipamorelin, which acts on the same receptor. The library entry is at MK-677 (Ibutamoren).

What the Human Trials Show

MK-677 has more randomized human data than most compounds in this category, which makes it possible to say clearly what it does and does not do.

Growth hormone and IGF-1. In a randomized trial in 32 healthy adults aged 64 to 81, two to four weeks of once-daily oral MK-677 enhanced pulsatile GH release and restored IGF-1 to young-adult levels, while fasting glucose rose [3]. In a two-year randomized, placebo-controlled trial in 65 healthy adults aged 60 to 81, MK-677 raised GH and IGF-1 to levels seen in healthy young adults [4].

Body composition. In that same trial, fat-free mass fell slightly on placebo but rose on MK-677, and body cell mass increased; abdominal visceral fat and total fat mass did not differ between groups, while limb fat increased more on MK-677 [4]. In 24 obese young men, eight weeks of MK-677 increased fat-free mass and transiently raised basal metabolic rate, without changing total or visceral fat [5]. In healthy volunteers on a calorie-restricted diet, MK-677 reversed diet-induced negative nitrogen balance [6].

Strength and function. In the two-year trial, the increase in fat-free mass did not produce changes in strength or function, though the authors noted the study was not powered for functional end points [4].

Hip fracture recovery. In a multicenter phase IIb trial in 123 older patients recovering from hip fracture, IGF-1 rose but most functional performance measures did not improve; gait speed improved, and the treated group had numerically fewer falls [7]. The trial was terminated early because of a safety signal of congestive heart failure in a limited number of patients, and the authors concluded MK-677 had an unfavorable safety profile in that population [7].

Alzheimer's disease. In a 12-month randomized trial of 563 patients with mild to moderate Alzheimer's disease, MK-677 raised IGF-1 substantially but had no effect on any measure of disease progression [8].

Sleep. A small crossover study in young and older adults reported increases in deep (stage IV) and REM sleep with MK-677 [9]. This is a small, early study and has not been confirmed in larger trials.

Bone. In a randomized trial of 292 postmenopausal women with osteoporosis, MK-677 increased markers of both bone formation and bone resorption. Combined with alendronate, it produced a larger gain in femoral neck bone density than alendronate alone, but not at the lumbar spine, total hip, or total body [10].

The pattern across trials is consistent: MK-677 engages its target and raises GH and IGF-1, but those biochemical changes have not translated into clinical benefit in the populations studied.

Side Effects

The side-effect profile comes from randomized trials rather than anecdote, which makes it more reliable than for most compounds in this category.

• Increased appetite. The most frequent side effect in the two-year older-adult trial; it subsided over a few months [4]. This follows from ghrelin-receptor agonism.
• Edema and muscle pain. Transient, mild lower-extremity edema and muscle pain were among the most common effects [4].

• Glucose and insulin sensitivity. Fasting glucose rose by about 0.3 mmol/L on average and insulin sensitivity decreased in older adults [4]. In obese young men, an oral glucose tolerance test showed impaired glucose homeostasis at two and eight weeks [5]. This matters for patients with prediabetes or diabetes.
• Weight gain. Body weight increased more on MK-677 than placebo over the older-adult trial [4].
• Cortisol. Cortisol rose modestly in older adults [4]; in obese young men the cortisol effect was transient [5].
• Heart failure signal. The hip-fracture trial was stopped early for congestive heart failure in a limited number of patients [7]. Given that fluid retention is a known effect, this is the most important safety signal for older or medically complex patients.

Regulatory Status in 2026

MK-677 is not FDA-approved for any indication. It is a small molecule, not a peptide, and FDA lists ibutamoren mesylate in 503A Category 2, substances that raise significant safety risks (FDA category list updated May 14, 2026), so it is not eligible for 503A compounding under FDA's interim policy. See our FDA peptide status tracker for changes. Our guide to which peptides can be compounded in 2026 explains how the interim categories work. MK-677 is also prohibited in sport by anti-doping authorities as a growth hormone secretagogue; tested athletes should check current rules.

How It Compares With Other GH-Axis Options

MK-677 is distinct from GHRH analogs such as sermorelin and tesamorelin, which act on a different receptor, and from peptide secretagogues such as ipamorelin, which share its receptor but are given parenterally and are short-acting. For the GHRH-versus-secretagogue distinction, see Sermorelin vs Ipamorelin.

Frequently Asked Questions

Is MK-677 a peptide?

No. MK-677 (ibutamoren) is a non-peptide small molecule taken by mouth. It acts on the same ghrelin receptor as peptide secretagogues like ipamorelin, which is why it is often grouped with them.

What does MK-677 actually do in human studies?

It raises growth hormone and IGF-1 and increases fat-free mass. In randomized trials it did not improve strength or function in healthy older adults, did not slow Alzheimer's disease, and did not improve most functional measures after hip fracture.

What are the main side effects of MK-677?

Increased appetite, mild leg swelling, muscle pain, weight gain, higher fasting glucose and reduced insulin sensitivity. A hip-fracture trial was stopped early because of a congestive heart failure signal in a limited number of patients.

Does MK-677 raise blood sugar?

Yes, in trials. Fasting glucose rose and insulin sensitivity decreased in older adults, and glucose tolerance worsened in obese young men. Prescribers typically weigh this carefully in patients with prediabetes or diabetes.

Is MK-677 FDA approved?

No. It is not approved for any indication, and FDA lists it in 503A Category 2 (significant safety risks). See our FDA peptide status tracker for current status.

What is the MK-677 dose?

This guide does not provide one. Dosing is a decision for the prescribing clinician, weighing the trial safety data above.

References

1. Howard AD, et al. A receptor in pituitary and hypothalamus that functions in growth hormone release. Science. 1996;273(5277):974-7. PubMed
2. Kojima M, et al. Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature. 1999;402(6762):656-60. PubMed
3. Chapman IM, et al. 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. J Clin Endocrinol Metab. 1996;81(12):4249-57. PubMed
4. Nass R, et al. Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Ann Intern Med. 2008;149(9):601-11. PubMed
5. Svensson J, et al. Two-month treatment of obese subjects with the oral growth hormone (GH) secretagogue MK-677 increases GH secretion, fat-free mass, and energy expenditure. J Clin Endocrinol Metab. 1998;83(2):362-9. PubMed
6. Murphy MG, et al. MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism. J Clin Endocrinol Metab. 1998;83(2):320-5. PubMed
7. Adunsky A, et al. MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture: a multicenter, randomized, placebo-controlled phase IIb study. Arch Gerontol Geriatr. 2011;53(2):183-9. PubMed
8. Sevigny JJ, et al. Growth hormone secretagogue MK-677: no clinical effect on AD progression in a randomized trial. Neurology. 2008;71(21):1702-8. PubMed
9. Copinschi G, et al. Prolonged oral treatment with MK-677, a novel growth hormone secretagogue, improves sleep quality in man. Neuroendocrinology. 1997;66(4):278-86. PubMed
10. Murphy MG, et al. Effect of alendronate and MK-677 (a growth hormone secretagogue), individually and in combination, on markers of bone turnover and bone mineral density in postmenopausal osteoporotic women. J Clin Endocrinol Metab. 2001;86(3):1116-25. PubMed

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