MK-677 for muscle and strength

The unusual one on this shelf

Two clarifications before anything else, because both are routinely got wrong.

MK-677 is not a peptide. It is an orally active non-peptide small molecule — a growth hormone secretagogue that mimics ghrelin, prompting the pituitary to release growth hormone.⁴ It is sold in peptide shops and discussed in peptide forums, but chemically it belongs to a different category entirely, which is also why it works as a tablet rather than an injection.

Unlike most of this shelf, it has real human trials. Merck developed it and took it into multi-year randomised studies. So for once we are not writing about an evidence vacuum. We are writing about what happens when a compound is properly tested — which turns out to be less flattering than the vacuum.

It does the hormonal thing, reliably

The pivotal study is a two-year, double-blind, placebo-controlled trial in 65 healthy adults aged 60 to 81, taking 25 mg of MK-677 daily.¹

It worked, at the level of hormones. Daily administration "significantly increased growth hormone and insulin-like growth factor I levels to those of healthy young adults," and did so in the normal pulsatile pattern rather than as a flat elevation.¹ In the later hip-fracture trial, IGF-1 rose by 51.4 ng/ml against placebo.²

If raising growth hormone were the goal, this compound would be an unambiguous success. It is not the goal. It is a surrogate for the goal.

What you actually gain

Here is the full body-composition result from that two-year trial, which is the single most useful thing on this page.

Work through the arithmetic, because nobody selling this does. Participants gained 2.7 kg of body weight. About 1.1 kg of it was fat-free mass — and 0.8 kg of that was intracellular water. Meanwhile limb fat rose by 1.1 kg, more than four times the placebo group's gain.

So the weight gained was roughly as much fat as lean, much of the lean was water, and one of the trial's two primary endpoints — reducing abdominal visceral fat — showed no significant difference at all.

Increased fat-free mass did not result in changes in strength or function. Nass et al., Annals of Internal Medicine, 2008¹

The trial that was stopped

The functional question was tested more directly in 123 elderly hip-fracture patients, randomised to 25 mg/day of MK-677 or placebo.² This population had the most to gain: recovering from fracture, losing function, exactly the people a muscle-preserving drug should help.

Gait speed improved modestly (p=0.011). Stair-climbing power did not (p=0.292). The authors state that there was "no improvement in MK-0677 treated patients in several other functional performance measures," and that "the increase in plasma IGF-1 levels was not paralleled by improvement in most functional performance measures."²

Then the trial ended before it was supposed to.

Trial was terminated early due to a safety signal of congestive heart failure in a limited number of patients... MK-0677 has an unfavorable safety profile in this patient population. Adunsky et al., Archives of Gerontology and Geriatrics, 2011²

That sentence is why MK-677 is not a prescription drug today. Merck had a compound that reliably raised growth hormone, ran it in the population that needed it most, and stopped the study over cardiac safety. The FDA cites this specific trial in its own assessment.³

The metabolic bill

The two-year trial also recorded what else changed while fat-free mass was going up.¹

Fasting blood glucose rose by an average of 0.3 mmol/L — about 5 mg/dL — and insulin sensitivity decreased (P=0.015). Cortisol rose by 47 nmol/L (P=0.020). Bone mineral density changes consistent with increased bone remodelling occurred. The most frequent side effects were increased appetite, which subsided over months, and transient mild lower-limb oedema and muscle pain.

Reduced insulin sensitivity is the one to sit with. It is a persistent, direction-of-travel-toward-diabetes change, reported in the trial most often cited as evidence the compound is safe and effective. It appears in essentially no marketing.

Where regulators landed

MK-677 occupies a stricter regulatory position than most compounds we have covered, and the distinction matters.

The FDA placed ibutamoren mesylate in category 2 — bulk drug substances that may present significant safety risks — for 503A compounding on 29 September 2023 and for 503B on 29 December 2022. Unlike BPC-157 and TB-500, whose nominations were later withdrawn, ibutamoren remains in category 2 today. FDA's stated rationale names the potential for congestive heart failure and cites the terminated hip-fracture trial directly.³

Sport Integrity Australia, the Australian government's anti-doping body, lists ibutamoren under WADA class S2.2.4 — prohibited at all times, in and out of competition — and states that no therapeutic use exemption would be granted for it. It is not on the Australian Register of Therapeutic Goods, has not been approved for human use, and their assessment notes plainly that this means "there is no toxicity data, and the extent of potential side effects remain unknown."⁴

Three claims, three answers

Read the three together and the compound's actual profile appears. It reliably moves hormones. It reliably moves a body-composition number that partly reflects water. It has not been shown to make anyone stronger or more capable — in either trial that looked.

Safety and unknowns

• Adverse events reported

  Increased appetite (subsiding over months), transient mild lower-extremity oedema, muscle pain, raised fasting glucose, decreased insulin sensitivity, raised cortisol, and bone remodelling changes.¹ Most seriously, a congestive heart failure signal sufficient to terminate a randomised trial early.²

• Longest human exposure studied

  Two years, in 65 healthy older adults.¹ This is by some distance the best-characterised compound on our peptides shelf — which is what makes the findings above meaningful rather than absent.

• Known interactions and at-risk groups

  The documented cardiac signal arose in elderly hip-fracture patients.² Anyone with cardiac risk, impaired glucose tolerance, or diabetes should treat the insulin-sensitivity finding as directly relevant. Trial populations were older adults; effects in young healthy people taking it for physique are not characterised.

• Regulatory status

  Not approved for human use in the US or Australia. Currently in FDA category 2 for both 503A and 503B compounding, on congestive-heart-failure grounds.³ Prohibited by WADA at all times under S2.2.4, with no therapeutic use exemption available.⁴

• What has not been characterized

  Effects beyond two years. Effects in young healthy adults — the group actually buying it. The magnitude and reversibility of the insulin-sensitivity change with long-term use. Whether the cardiac signal extends beyond frail elderly populations. And, as always for a substance sold as a research chemical, what any given product contains.

How this was graded

Two reasons this stays at Emerging despite unusually good individual trials. The verified pooled population is 188, just under the floor. And both pivotal trials trace to Merck's development programme for the compound — under our definition of an independent group, that is closer to one programme than to two unaffiliated confirmations. Good trials are not the same as replicated trials.

Bottom line

Sources

1. Nass R, Pezzoli SS, Oliveri MC, Patrie JT, Harrell FE Jr, Clasey JL, Heymsfield SB, Bach MA, Vance ML, Thorner MO. Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Annals of Internal Medicine. 2008;149(9):601–611. PMID 18981485
2. Adunsky A, Chandler J, Heyden N, Lutkiewicz J, Scott BB, Berd Y, Liu N, Papanicolaou DA. MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture: a multicenter, randomized, placebo-controlled phase IIb study. Archives of Gerontology and Geriatrics. 2011;53(2):183–189. ClinicalTrials.gov NCT00128115. PMID 21067829
3. US Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. Ibutamoren mesylate, category 2 — 503A added 29 September 2023, 503B added 29 December 2022. Content current as of 22 April 2026. fda.gov
4. Sport Integrity Australia. Ibutamoren (MK 677) information. sportintegrity.gov.au

Search results for this compound are dominated by vendor and marketing pages. Under our sourcing standard none are usable as evidence for any mark, and none were used here.