MK-677: The Same Molecule Is in a Phase 3 Trial and on the Grey Market

01What it is

A small molecule, taken by mouth, not a peptide. Merck called it L-163,191. It is an agonist at the ghrelin receptor GHSR1a, and the human receptor has been solved with ibutamoren sitting in it. (PMID 34737341) Not a SARM, not a steroid, though it is usually sold beside them. The receptor was identified in 1996. (PMID 8688086) Ghrelin, the natural signal that fits it, was not characterised for another three years. The imitation was in hand before anyone had met the original.

02What the trials found

Two years, 65 older adults aged 60 to 81, randomised, double blind, placebo controlled, 25 mg daily. The longest human study of this compound. Fat free mass went -0.5 kg on placebo and +1.1 kg on MK-677, body weight 0.8 against 2.7 kg, visceral and total fat unchanged. (PMID 18981485) Then the sentence the study is famous for: "Increased FFM did not result in changes in strength or function."

Fat free mass is everything you are that is not fat, and most of that is water. That same trial reported swelling in the lower legs.

Two hip fracture trials, both inconclusive. Bach 2004: 161 patients over 65, six months, IGF-1 up 84 percent against 17, no difference in function. (PMID 15066065) Adunsky 2011: 123 patients, 25 mg a day for 24 weeks. IGF-1 up 51.4 ng/mL, the Short Physical Performance Battery up 0.7 points, stair climbing power flat. The trial stopped early over suspected congestive heart failure. (PMID 21067829)

Then Alzheimer's. 563 patients, 25 mg a day for 12 months, IGF-1 up 60.1 percent at six weeks and 72.9 percent at 12 months, no difference on any cognitive, functional or dementia measure. (PMID 19015485) The largest study ever run on this compound found nothing. Smaller work runs the same: 24 obese men, IGF-1 up about 40 percent (PMID 9467542), 22 haemodialysis patients up 65 percent (PMID 28340044).

Look at the pattern, not any one result. 40 percent, 51 ng/mL, 60, 65, 72.9, 84. IGF-1 is the one thing this compound never failed to raise, across six populations and three decades. Then every trial measured the thing it actually cared about and found nothing.

03The trial that is still running

Merck's MK-0677 and Lumos Pharma's LUM-201 are the same molecule, and a 2022 paper in Hormone Research in Paediatrics opens by saying so. (PMID 35354138) It is in phase 3 right now. NCT06948214, recruiting, start 20 May 2026, 150 treatment naive prepubertal children on oral LUM-201 at 1.6 mg per kilogram per day. At the same moment the same compound is an unapproved drug on the grey market.

The molecule did not change. The paperwork did.

The paediatric data is not flattering either. In 68 prepubertal children with growth hormone deficiency, six months gave a height velocity of 4.5 cm/year on placebo, 6.0 on 0.4 mg/kg/day and 6.9 on 0.8 mg/kg/day, against 11.1 for injected growth hormone. (PMID 33982679) Oral growth hormone, tested in the exact population it was built for, and losing.

04How it compares

MK-677 gets sold as the oral version of the peptides beside it.

Read the last column. None of it transfers sideways.

05Where 25 mg came from

In 1996 Chapman and colleagues ran a randomised, double blind, placebo controlled dose ranging study in 32 healthy adults aged 64 to 81, on 2, 10 or 25 mg once daily for 14 or 28 days. At 25 mg for two weeks, 24 hour growth hormone rose about 97 percent, and IGF-1 went from 141 to 265 µg/L by four weeks. (PMID 8954023)

That is the whole origin of 25 mg. It was the biggest of three doses tested, it produced the biggest numbers, and it became the standard adult dose. One bone study pushed 30 healthy elderly subjects to 50 mg for two weeks (PMID 10404019). Nothing higher has been published. Community convention is 10 to 25 mg at night, sourced from vendors and forums quoting each other.

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mg per day · log scale

derived from researchcommunity convention

1. 1Lowest arm of the 1996 dose ranging study · 2 mg per dayNobody uses it.
2. 2The one documented real world average · 6.7 mg per dayA 2026 hair testing paper. 600 mg over 90 days, an average, not a daily dose.
3. 3The community convention · 10 to 25 mg per dayWhere vendor pages and forums converge. No primary source. They cite each other.
4. 4Top arm of the 1996 study · 25 mg per dayThe number everything else rests on. Largest of three arms in 1996.
5. 5Highest dose in the published adult literature · 50 mg per dayOne bone programme, 30 elderly subjects, two weeks. Nothing higher is published.

The children get a rule. The adults get a number. A per kilogram dose is an instruction that still works on somebody it has never met. A flat 25 mg is a leftover from the last group it was measured in, 32 pensioners in 1996.

06What could go wrong

The 1996 study already found fasting glucose up significantly (PMID 8954023), and the two year trial saw insulin sensitivity down (PMID 18981485).

The obese men trial is the one to read. Fasting glucose and insulin were unchanged after eight weeks. A glucose tolerance test found impairment at two weeks and at eight. (PMID 9467542) The fasting labs missed what the challenge test caught. A clean fasting panel here is reassurance from a test known to understate this.

The most common side effects in the two year trial were increased appetite, mild swelling in the lower legs, and muscle pain. (PMID 18981485) A forum log files those same three under week two going great. Nothing in the body is different. Only the column heading.

Adunsky stopped early over suspected heart failure and the authors called the safety profile unfavourable. That much is published. The widely repeated four cases against one on placebo is not. The abstract says only a limited number of patients and the full text is paywalled, so those numbers come from industry write-ups and I am not printing them as fact.

The other risks are not medical. Not approved by FDA, so it is not legal in supplements or any consumer product. WADA prohibits it at all times, under S2, added by name for 2024. It shows up in hair four weeks after a single 10 mg dose. (PMID 40882886)

FDA has also named it in a warning letter to a compounding pharmacy. Warning letter 594743, dated 1 April 2020, went to Tailor Made Compounding LLC of Nicholasville, Kentucky, and under the heading "Failure to Meet the Conditions of Section 503A" it lists this compound among the bulk substances the firm had compounded with, the stated ground being that products made from those substances are not eligible for the section 503A(a) exemptions, since the substance is not the subject of an applicable USP or NF monograph, is not a component of an FDA approved human drug, and does not appear on the 503A bulks list. That is one pharmacy being told about its own compounding, and not an action against the molecule or against anybody else selling it. Note the spelling, because it is how the letter gets missed: FDA writes MK 677, no hyphen, so a search on the hyphenated form used here can come back empty.

07What nobody knows

Whether it does anything in anyone young or trained. I found nothing randomised outside pensioners and patients.

The 24 hour half life and the 60 to 70 percent bioavailability on every vendor page have no primary human source I could find, and the pages contradict each other.

No published statement says why Merck stopped, so anyone telling you it was heart failure is extrapolating.

08My take

The interesting thing about MK-677 is not that the evidence is weak. It is that the evidence is unusually strong, and it says no.

Hundreds of people in randomised placebo controlled trials, a solved receptor structure, a sponsor, a live phase 3. And in adults it failed every trial that measured something a person would care about. The dose says the same thing. The children in that phase 3 get 1.6 mg per kilogram per day, and adults get the top arm of a study of 32 pensioners in 1996, carried forward ever since.

If you have taken MK-677 and had bloods drawn, I want to know one thing. Did anyone give you a glucose tolerance test, or only a fasting panel? The obese men trial is why that matters, and I have never once seen the distinction raised in a log.

Frequently asked

Is MK-677 a SARM?+

No. It is a small molecule taken by mouth, not a peptide and not a steroid. It is usually sold beside SARMs, which is where the confusion comes from.

Is MK-677 FDA approved?+

It is not approved by the FDA, so it is not legal in supplements or any consumer product. WADA prohibits it at all times under S2, added by name for 2024, and it has been detected in hair four weeks after a single 10 mg dose.

Is MK-677 still being developed, or did Merck drop it?+

Merck's MK-0677 and Lumos Pharma's LUM-201 are the same molecule, and a 2022 paper in Hormone Research in Paediatrics opens by saying so. NCT06948214 is recruiting, start date 20 May 2026, 150 treatment naive prepubertal children on oral LUM-201 at 1.6 mg per kilogram per day. As for Merck, no published statement says why they stopped, so anyone telling you it was heart failure is extrapolating.

Where did the 25 mg dose come from?+

One study. In 1996 Chapman and colleagues ran a randomised, double blind, placebo controlled dose ranging study in 32 healthy adults aged 64 to 81, on 2, 10 or 25 mg once daily for 14 or 28 days. 25 mg was the largest of the three doses tested, it produced the largest numbers, and it became the standard adult dose. The 10 to 25 mg at night that circulates as community convention has no primary source behind it, only vendors and forums quoting each other.

Does MK-677 actually build muscle?+

In the longest human trial, two years in 65 adults aged 60 to 81 on 25 mg daily, fat free mass changed by minus 0.5 kg on placebo and plus 1.1 kg on MK-677, body weight by 0.8 against 2.7 kg, with visceral and total fat unchanged. The authors report that the increased fat free mass did not result in changes in strength or function. Researching this entry, I found nothing randomised in young trained adults.

Does MK-677 raise blood sugar?+

The 1996 study found fasting glucose up significantly, and the two year trial found insulin sensitivity down. The trial to read is the one in 24 obese men: fasting glucose and insulin were unchanged after eight weeks, while a glucose tolerance test found impairment at two weeks and at eight. The fasting labs missed what the challenge test caught, so a clean fasting panel here is reassurance from a test known to understate this.

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This content is for educational and informational purposes only and is not medical advice. Peptides discussed are research compounds and may not be approved for human use. Nothing here should be used to diagnose, treat, cure, or prevent any disease. Always consult a qualified healthcare professional before starting any peptide, supplement, or protocol. Individual responses vary. Do not self-administer compounds without proper medical supervision.