MK-677 (Ibutamoren): Oral Ghrelin Mimetic Research and Risks

Abstract still life: a small spherical brass object resting in a ceramic spoon on linen — **MK-677 (Ibutamoren).** Illustration, not a product photo.

Research compound. Not approved by FDA Philippines for human use unless stated. Nothing here is a dosing recommendation or medical advice.

What it is

MK-677, also called ibutamoren, is not a peptide. It is a small-molecule drug, taken by mouth, that Merck developed in the 1990s as an oral alternative to injectable GH-releasing peptides. It mimics ghrelin at the growth hormone secretagogue receptor, so it sits in the same family as ipamorelin and GHRP-6, but it survives digestion and is absorbed from the gut.

It is often sold alongside SARMs in gym circles. That grouping is about marketing, not pharmacology: MK-677 does not touch the androgen receptor. We cover it here because it works through the same GH axis as the peptides in this library.

How it works

MK-677 activates the ghrelin receptor in the pituitary and hypothalamus, which increases the natural pulses of growth hormone. IGF-1 rises in turn. A review of the secretagogue literature reports a serum half-life of about 4.7 hours and high oral bioavailability, which is why one dose a day was enough in trials.

In the 1996 study in older adults, 25 mg daily nearly doubled mean 24-hour GH (up 97%) by making existing pulses bigger and raising the troughs between them, without adding new pulses. IGF-1 rose from 141 to 265 mcg/L over four weeks, into the range of young adults.

Because it also acts like ghrelin, the hunger hormone, increased appetite is its most noticeable effect.

What the research found

Human studies

Nass and colleagues (2008) ran the longest trial: two years, double-blind and placebo-controlled, in 65 healthy adults aged 60 to 81. After one year on 25 mg daily:

GH and IGF-1 rose to young-adult levels
fat-free mass rose 1.1 kg on MK-677 and fell 0.5 kg on placebo
body weight rose 2.7 kg on MK-677 vs 0.8 kg on placebo
abdominal visceral fat and total fat mass did not differ between groups, though limb fat rose more on MK-677
fasting glucose rose by an average of 0.3 mmol/L (5 mg/dL), insulin sensitivity fell and cortisol rose
LDL cholesterol fell slightly

The extra lean mass did not translate into better strength or physical function.

Chapman and colleagues (1996) tested 2, 10 and 25 mg daily in 32 adults aged 64 to 81 for up to four weeks. GH rose with dose. Mean fasting glucose on MK-677 rose from 5.4 to 6.8 mmol/L at four weeks, and prolactin rose 23% while staying in the normal range.

Copinschi and colleagues (1997) studied sleep. In 8 young adults, 25 mg at bedtime increased stage IV (deep) sleep by about 50% and REM sleep by more than 20% versus placebo. In 6 older adults, REM sleep rose by nearly 50%.

Adunsky and colleagues (2011) gave 25 mg daily or placebo to 123 older adults after hip fracture. IGF-1 rose, gait speed improved slightly, but most functional measures did not. The trial was stopped early because of a congestive heart failure safety signal in a limited number of patients, and the authors concluded MK-677 has an unfavourable safety profile in that population.

Side effects reported in studies

Increased appetite, the most common effect in the 2-year trial, which faded over a few months
Mild, temporary swelling of the lower legs and muscle pain
Higher fasting glucose and lower insulin sensitivity, seen in both the 4-week and 2-year trials
Rises in cortisol and prolactin, within the normal range in the 1996 study
Congestive heart failure signal in frail older hip fracture patients

The US FDA lists ibutamoren among bulk substances that pose significant safety risks for compounding, citing the potential for congestive heart failure in certain patients.

MK-677 vs ipamorelin

	MK-677	Ipamorelin
Type	Small molecule	Five amino acid peptide
Route	Oral	Injection
GH pattern	Raised all day with daily dosing	Single pulse, back to baseline within hours
Longest human trial	2 years (older adults)	7 days (surgical patients)
Known signals	Glucose, appetite, oedema, heart failure in hip fracture	Few data

Status in the Philippines

No MK-677 product is registered with FDA Philippines, and it has never been approved as a medicine anywhere. It is not a controlled substance under RA 9165. Locally it is sold as capsules or liquid through gym and research-chemical channels, often listed next to SARMs. Given the glucose findings, fasting glucose and HbA1c are the lab tests the trials point to; see bloodwork in the Philippines.

Storage

As a small molecule, MK-677 is more heat-tolerant than injectable peptides and does not need reconstitution. Keep capsules or liquid sealed, dry and away from direct sun. Liquid suspensions from research suppliers vary in formulation, so follow the label; refrigeration does no harm in a Philippine summer.

Doses used in published research

What investigators actually administered, as reported in the cited study. This is a record of the literature, not a recommendation.

Study	Population	Regimen
Nass et al., Ann Intern Med 2008	Healthy adults aged 60 to 81	25 mg by mouth once daily, up to 2 years
Chapman et al., J Clin Endocrinol Metab 1996	Healthy adults aged 64 to 81	2, 10 or 25 mg by mouth once daily, study periods of 14 and 28 days
Copinschi et al., Neuroendocrinology 1997	Healthy young adults 18 to 30; older adults 65 to 71	Young: 5 or 25 mg at bedtime for 7 days. Older: 2 mg then 25 mg at bedtime, 14 days each
Adunsky et al., Arch Gerontol Geriatr 2011	Older adults recovering from hip fracture	25 mg by mouth daily, planned 24 weeks; stopped early

Common questions

Is MK-677 a peptide or a SARM?

Neither. MK-677 (ibutamoren) is a small-molecule drug taken by mouth that mimics ghrelin at its receptor. It raises growth hormone through the pituitary, which is why it is grouped with GH peptides such as ipamorelin, but it has no amino acid chain and does not act on androgen receptors.

Does MK-677 raise blood sugar?

Yes, in trials. In the 2-year study in adults aged 60 to 81, fasting glucose rose by an average of 0.3 mmol/L (5 mg/dL) and insulin sensitivity fell. In a 4-week study in older adults, mean fasting glucose on MK-677 rose from 5.4 to 6.8 mmol/L.

Why was MK-677 never approved?

Its trials raised GH and IGF-1 and increased lean mass, but did not improve strength or function in healthy older adults. A hip fracture trial was stopped early because of a congestive heart failure safety signal in a small number of patients.

Does MK-677 improve sleep?

One small 1997 study found more deep sleep and REM sleep on 25 mg at bedtime, in 8 young and 6 older adults. It has not been confirmed in a larger trial.