MK-677 (Ibutamoren)
MK-677 is ibutamoren. It is an oral drug, not a peptide. In a controlled study, it made the body release more growth hormone. (PMID 18981485; read 25 Aug 2026). GSRS lists it as a chemical substance (GSRS; read 25 Aug 2026). The trial used a random draw with 65 healthy adults aged 60 to 81 (PMID 18981485; read 25 Aug 2026). At 12 months, fat-free mass rose 1.1 kg with MK-677 (same source and date). It fell 0.5 kg with placebo. The trial found no clear change in visceral or total fat. A separate Merck trial stopped early after a heart-failure signal (EudraCT 2005-002509-22; read 25 Aug 2026).
Which names and identifiers belong to MK-677?
GSRS gives the INN IBUTAMOREN (GSRS; read 25 Aug 2026). It gives UNII GJ0EGN38UL. Its primary CAS is 159634-47-6. It also lists L-163,191.
The human paper uses MK-677 (PMID 18981485; read 25 Aug 2026). A Merck report says MK-0677 is ibutamoren mesylate (EudraCT results; read 25 Aug 2026).
EU trial records give CAS 159752-10-0 for the mesylate salt. The live record also stores MK 677 and Nutrabol as lookup aliases. This page makes no product claim from either label.
What did the trial in older adults find?
The double-blind trial had 43 people on MK-677 and 22 on placebo (PMID 18981485; read 25 Aug 2026). The main test covered 12 months.
NIH grants DK-32632 and RR-00847 supported the work (full paper; read 25 Aug 2026). German Research Foundation grants Na 317/1-1 and Na 317/1-2 helped support one author. Merck supplied MK-677 and placebo. Two of ten authors worked at Merck Research Laboratories.
| Result at 12 months | Placebo | MK-677 | Source |
|---|---|---|---|
| Fat-free mass | -0.5 kg (95% CI -1.1 to 0.2) | +1.1 kg (0.7 to 1.5) | PMID 18981485 |
| Body cell mass | -1.0 kg (95% CI -2.1 to 0.2) | +0.8 kg (-0.1 to 1.6) | PMID 18981485 |
| Body weight | +0.8 kg (95% CI -0.3 to 1.8) | +2.7 kg (2.0 to 3.5) | PMID 18981485 |
| Visceral fat | +4.2 cm² (95% CI -6.2 to 14.5) | +8.4 cm² (1.6 to 15.3) | PMID 18981485 |
The fat-free-mass result had p < 0.001 (PMID 18981485; read 25 Aug 2026). The body-cell-mass result had p = 0.021 (same source and date). The weight result had p = 0.003 (same source and date).
Mean 24-hour growth hormone rose 1.8-fold (95% CI 1.56 to 2.0; p < 0.001; PMID 18981485; read 25 Aug 2026). IGF-I rose 1.5-fold (95% CI 1.4 to 1.6; p < 0.001; same source and date).
The visceral-fat result had p = 0.68 (PMID 18981485; read 25 Aug 2026). The trial missed that primary endpoint. Total fat did not clearly differ. Limb fat rose 1.1 kg with MK-677 and 0.24 kg with placebo (p = 0.001; same source and date). Thigh-muscle area did not rise. The gain in fat-free mass did not improve strength or function.
The NIH author copy has no conflict section. That is not a statement that no conflict existed.
What else did the same study record?
| Finding | Placebo | MK-677 | Source |
|---|---|---|---|
| Fasting-glucose change | 0.0 mmol/L (95% CI -0.3 to 0.2) | +0.3 mmol/L (0.1 to 0.4) | PMID 18981485 |
| More appetite | 8/22 (36%) | 29/43 (67%) | PMID 18981485 |
| Mild short-term oedema | 6/22 (27%) | 19/43 (44%) | PMID 18981485 |
| Short-term muscle pain | 2/22 (9%) | 14/43 (33%) | PMID 18981485 |
| Joint pain | 17/22 (77%) | 25/43 (58%) | PMID 18981485 |
| 24-hour cortisol change | -18 nmol/L (95% CI -55 to 19) | +47 nmol/L (28 to 71) | PMID 18981485 |
The glucose result had p = 0.015. Insulin sensitivity fell. Mean HbA1c fell 0.1 points with placebo and rose 0.2 points with MK-677 (p = 0.002; PMID 18981485; read 25 Aug 2026).
The appetite result had p = 0.02. Appetite went back to normal within three months for half of the affected MK-677 group. The oedema, muscle-pain, and joint-pain results were not clear group differences (PMID 18981485; read 25 Aug 2026).
The body of PMID 18981485 reports tongue adenocarcinoma in one MK-677 participant at 12 months. It reports a heart attack in another participant seven days after starting MK-677. Both left the trial. The paper also reports renal-cell carcinoma in one placebo participant.
At the end of year two, colon cancer was found in one participant. She had MK-677 in year one and placebo in year two. The paper reports these events without saying that MK-677 caused all of them (read 25 Aug 2026).
Why did the hip-fracture trial stop early?
Five EU country records mark trial 2005-002509-22 as ended early. Each records approval from its national drug agency. Merck sponsored the phase 2 trial.
Merck's public report says the trial stopped after a congestive heart failure signal (EudraCT results; read 25 Aug 2026). Four of five heart-failure cases were in the MK-0677 group.
| Merck safety result | MK-0677 | Placebo | Source |
|---|---|---|---|
| One or more adverse events | 48/62 (77%) | 33/60 (55%) | 2005-002509-22 report |
| Serious adverse events | 15/62 (24%) | 8/60 (13%) | 2005-002509-22 report |
| Stopped due to adverse events | 7/62 (11.3%) | 4/60 (6.7%) | 2005-002509-22 report |
| Heart-failure cases | 4 | 1 | 2005-002509-22 report |
One MK-0677 participant died after sepsis and pneumonia. The investigator did not link those events to the study drug. The report found higher blood pressure with MK-0677. It also found higher body weight (EudraCT 2005-002509-22; read 25 Aug 2026).
What EU status is established?
Ibutamoren has been studied in EU trials approved by national drug agencies. The 2005 trial ended early. The 2020 phase 2 record is completed (EudraCT 2020-000874-92; read 25 Aug 2026). The 2022 phase 2 record is also completed (EudraCT 2022-001695-34; same date).
The records do not show a current EU trial. They do not settle current EU approval for sale. The available EMA workbook is dated 5 December 2023.
The live register uses the field investigational. This page uses it only for the past trial records. It makes no claim about current sale approval.
What does evidence tier B mean here?
Controlled human studies exist. The record remains tier B (field checked 15 Aug 2026). No named use with current sale approval and phase 3 data is established here.
What does this register entry cover?
This entry covers identity, selected human results, measured harms, and the EU trial record. It does not establish what is in a product. No sourced first-observed month is used.