MK-677

MK-677 binds the growth hormone secretagogue receptor, GHS-R1a, on the pituitary and in the hypothalamus, the same receptor ghrelin and the GHRP peptides use. The pituitary answers with more growth hormone, released in pulses as it normally is. Growth hormone then signals the liver to make IGF-1, which carries much of its effect on tissues.

A 1997 University of Virginia study showed both the power and the limits of that chain. Nine young men with severe growth hormone deficiency, all treated with growth hormone as children, took MK-677 or placebo for four days, with blood drawn every 20 minutes for 24 hours before and after. Average 24-hour growth hormone rose by about 80 percent and IGF-1 rose in every subject.

The detail worth noticing is who responded most. The growth hormone rise was largest in the men who were least deficient to begin with. MK-677 amplifies a pituitary’s own output, so it needs a pituitary with something left to amplify. In healthy older adults with working pituitaries, a later trial found it brought growth hormone and IGF-1 up to the levels of healthy young adults.

The same receptor carries other messages. It drives appetite, it can nudge the stress axis, and growth hormone itself opposes insulin. In the four-day study, fasting and after-meal insulin and after-meal glucose rose, an early sign of the metabolic trade-off the longer trials would confirm.¹⁶¹¹

The cleanest early test of MK-677 as an anabolic drug came from Merck in 1998. Eight healthy volunteers aged 24 to 39 followed a strict low-calorie diet for two 14-day periods, taking MK-677 or placebo during the second week of each. Dieting alone made them lose body protein, measured as nitrogen lost in urine.

MK-677 reversed that. During the treatment week, average nitrogen balance was slightly positive on the drug and clearly negative on placebo, meaning the body held on to protein despite the calorie cut. IGF-1, which had fallen with dieting, rose back above its starting level on MK-677, and the volunteers had no clinically significant adverse effects.

A Swedish trial the same year tried it in 24 obese men aged 18 to 50 for eight weeks. IGF-1 rose about 40 percent and fat-free mass increased, but no significant change in total or visceral fat was detected. Resting metabolic rate rose at two weeks and was no longer different at eight. An oral glucose tolerance test showed worse glucose handling at both checkpoints, while the cortisol rise was only transient.

Read together, the short trials show an anabolic, protein-sparing drug with no demonstrated fat loss, and the obesity trial found blood sugar harder to control. The longer studies that followed measured different outcomes, but those threads keep surfacing.⁸⁹

The landmark study appeared in Annals of Internal Medicine in 2008. A University of Virginia team randomized 65 healthy adults aged 60 to 81 to daily MK-677 or placebo in a two-year, double-blind trial. The question was whether restoring youthful growth hormone could stop the slow loss of muscle that leads to frailty.

The hormones did exactly what was hoped. Growth hormone and IGF-1 rose to the range of healthy young adults. Over a year, fat-free mass rose by 1.1 kg on MK-677 and fell by 0.5 kg on placebo. Body weight rose by 2.7 kg on the drug against 0.8 kg on placebo, and some of the gap was fat, since limb fat rose more on MK-677 while abdominal visceral fat did not differ.

Then came the result that matters most. The extra fat-free mass did not translate into any change in strength or function. The authors noted their trial was not large or long enough to judge functional outcomes, which is fair, but the people who took the drug for a year were not measurably stronger.

Side effects were mostly mild. Appetite rose and settled within a few months, and mild leg swelling and muscle pain came and went. Fasting glucose rose by about 5 mg/dL, insulin sensitivity fell and cortisol rose, while LDL cholesterol dipped slightly and bone mineral density changed in a way consistent with faster remodeling. Two-year exploratory analyses confirmed the one-year picture.¹¹

Growth hormone and deep sleep are tightly linked, and a 1997 Brussels study asked whether MK-677 would change sleep itself. Eight young adults aged 18 to 30 took MK-677 or placebo for three 7-day periods in a crossover design, and six adults aged 65 to 71 took two 14-day courses of the drug, compared with their own baseline.

In the young adults, the higher dose increased stage IV sleep, the deepest stage, by about 50 percent and REM sleep by more than 20 percent compared with placebo. Nights with abnormal sleep patterns fell from 42 percent to 8 percent. In the older adults, REM sleep rose by nearly half and arrived sooner after falling asleep.

The authors suggested MK-677 might improve sleep quality and correct the age-related fall in growth hormone at the same time. The study was small and short, though, and the abstracts of the long trials cited here do not report sleep outcomes, so this remains a promising early signal.⁷

Most older adults admitted with a broken hip lose function, and earlier studies hinted MK-677 might help recovery. A multicenter phase IIb trial tested that in 123 elderly hip fracture patients, 62 on MK-677 and 61 on placebo, for 24 weeks.

IGF-1 rose by about 51 ng/mL over placebo, so the drug engaged its target. Gait speed improved modestly. Stair-climbing power was not significantly better, several other performance measures showed no improvement, and a trend toward fewer falls did not reach significance.

The trial was stopped early because of a safety signal of congestive heart failure in a limited number of patients. The investigators concluded that MK-677 has an unfavorable safety profile in this population, and FDA’s compounding page cites this trial for its heart failure concern.

Why heart failure would appear is not settled. One plausible link, and it is only a hypothesis, is fluid retention, since growth hormone holds salt and water and leg swelling was common even in healthy older adults on MK-677. In frail patients with less cardiac reserve, a little extra fluid can matter a great deal.¹²¹³¹¹

The largest MK-677 trial cited here was not about muscle. In animals, IGF-1 helps clear beta-amyloid, the protein that builds up in Alzheimer’s disease, and IGF-1 levels fall with age and fall further in Alzheimer’s. Merck randomized 563 people with mild to moderate Alzheimer’s to MK-677 or placebo for 12 months.

IGF-1 rose 60 percent within six weeks and 73 percent by a year. On all four measures of thinking, daily function and overall change, the MK-677 group did no better than placebo. The authors noted that despite clear evidence the drug engaged its target, it did not slow the disease.

Line the big trials up and the pattern is hard to miss. In healthy older adults, lean mass rose and strength did not. After hip fracture, IGF-1 rose and most function did not. In Alzheimer’s, IGF-1 rose by nearly three-quarters and the disease went on. Each time, MK-677 did precisely what it was designed to do on the lab report.

That is the most useful thing MK-677 can teach anyone interested in growth hormone. IGF-1 is a messenger. Raising it tells tissues to grow, but whether they can depends on loading, protein, sleep, insulin sensitivity and the disease in front of you. A rising IGF-1 confirms the drug is working on its receptor, and it tells you very little about whether you are getting better.¹⁰¹¹¹²

The everyday side effects come straight from the biology. Appetite rises, usually settling over a few months. Mild leg swelling and muscle pain are common early on, and body weight climbs, partly as fat.

Blood sugar is the consistent metabolic cost. In the two-year trial fasting glucose rose by about 5 mg/dL and insulin sensitivity fell. The eight-week obesity trial found worse glucose tolerance, and even the four-day study saw insulin and after-meal glucose rise. Cortisol results vary by study, from no change in some to a modest, lasting rise in the two-year trial.

The serious concern is the heart. The hip fracture trial stopped early for a congestive heart failure signal, and FDA’s compounding page lists ibutamoren mesylate for both 503A and 503B because of the potential for congestive heart failure in certain patients.

Anyone with heart failure, heart disease or leg swelling, diabetes or prediabetes, a personal history of cancer, a pregnancy or a place in tested sport should take MK-677 to a clinician as a question first.^119681213

Each human MK-677 study here that measured glucose handling found it got worse, though none establishes a validated monitoring protocol. As general baseline context for a clinician, fasting glucose, fasting insulin and HbA1c describe that system, and HbA1c gives a three-month average that one morning reading cannot.

Cortisol findings varied across studies, rising modestly in the two-year trial and only briefly in the obesity trial, so a single value is context rather than a routine check. A clinician weighing MK-677 will also want your heart history, blood pressure and any swelling on the record.

This is how Vitals Vault approaches anything in the growth hormone family. A blood panel at Quest Diagnostics comes first, a licensed clinician reviews your results and history and decides what, if anything, fits, and any course ends with a retest of the same markers.¹¹⁹⁶¹²

MK-677 is not an FDA-approved drug. FDA’s April 2026 compounding page lists ibutamoren mesylate for both 503A and 503B, citing the potential for congestive heart failure. The enforcement discretion FDA granted on October 29, 2026 covers six peptides, and MK-677 is not among them.

In sport, growth hormone secretagogues fall in the S2 class of the World Anti-Doping Agency’s Prohibited List, which applies in and out of competition.

Capsules and liquids sold online for research use only are not made for people and fall outside FDA’s policy.¹³¹⁴¹⁵

MK-677 is an oral ghrelin mimic with a longer human trial record than most growth hormone secretagogues. It reliably raises growth hormone and IGF-1 and adds lean mass. In trials, it did not make people stronger, improve most measures of function after a fracture or slow Alzheimer’s. It also raises appetite and blood sugar, and in frail older patients it carried a heart failure signal.

If MK-677 interests you, look past the IGF-1 number. The better question is what result you actually want, whether strength, sleep, body composition or something else, and whether anything in the trials shows MK-677 moving that result rather than just the hormone.¹¹¹²¹⁰