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Growth hormone axis

MK-677 (Ibutamoren)

Also called Ibutamoren mesylate, MK-0677, LUM-201

MK-677 (ibutamoren) is a pill, not a peptide, that copies ghrelin to raise growth hormone and IGF-1. Merck tested it in many human trials in the 1990s–2000s, but it never became an approved drug. A trial in hip-fracture patients was stopped early because of possible heart failure.

Late-stage trialsTested in large human trials (phase 2b/3) but not yet approved in the US.

All printable flashcards

Illustration only. MK-677 (Ibutamoren) is not a peptide.

Overview

MK-677 (ibutamoren) is a pill, not a peptide, that copies ghrelin to raise growth hormone and IGF-1. Merck tested it in many human trials in the 1990s–2000s, but it never became an approved drug. A trial in hip-fracture patients was stopped early because of possible heart failure.

How it works

Established: an orally active ghrelin-receptor (GHS-R1a) agonist that raises growth hormone pulses and IGF-1 levels. It also increases appetite and can raise blood sugar.

What research shows

  • Alzheimer's disease RCT (Sevigny 2008, n=563, 12 months): no benefit on cognition or function.
  • Healthy older adults (Nass 2008, n=71, 1 year): fat-free mass rose 1.1 kg; femoral neck bone density declined.
  • Hip fracture: Bach 2004 (n=161, 6 months) showed no overall functional benefit; Adunsky 2011 (n=123) stopped early for a heart-failure signal (6.5% vs 1.7%).
  • Children with GH deficiency (Bright 2021, n=68, 6 months): height velocity 6.0–6.9 cm/yr vs 4.5 on placebo and 11.1 on growth hormone.
  • Postmenopausal osteoporosis (Murphy 2001, n=292): femoral neck density improved only when combined with alendronate.

Doses studied in people

Study or labelDose usedSource
Adult RCTs (Alzheimer's n=563; older adults n=71; hip fracture n=161 and n=123; obese men n=24)25 mg orally once daily for 8 weeks to 12 months1
Pediatric GH deficiency RCT (Bright 2021, n=68)0.4 or 0.8 mg/kg/day orally for 6 months1
Adults with severe GH deficiency (Chapman 1997, n=9)10 or 50 mg/day orally, two 4-day periods1

Trial doses are summarized from FDA's 2024 review of the published literature; MK-677 is not approved at any dose.

Read this first: these are the amounts given to participants in published studies or written on official prescribing labels, reported for reference. They are not recommendations. Trial doses were chosen for specific patients under medical supervision, and a dose that is safe in one person can be harmful in another.

Weekly protocol

How the schedule looks week by week. Each chart says where it comes from: a prescribing label, a clinical trial, or a protocol commonly reported online.

Older-adult RCT (Nass et al., 2008)

Clinical trial

One week

D1D2D3D4D5D6D7

Once daily · Oral

Dose by week

25 mgwk 1–52
Course
12 months
Note
25 mg once daily is the dose used across the adult trials (8 weeks to 12 months) summarized by FDA. Not approved at any dose.
Source
FDA briefing document, Pharmacy Compounding Advisory Committee, Oct 29, 2024: ibutamoren mesylate (summary of published trials)

Reference only, not a recommendation. Label and trial schedules were set for specific patients under medical supervision. Use the calculator only to understand the arithmetic.

Safety

  • A hip-fracture trial (Adunsky 2011) was stopped early for a congestive heart failure signal (6.5% vs 1.7% on placebo); FDA lists potential heart failure as its main safety concern.
  • PCAC members cited fluid retention, heart failure and high blood sugar (Oct 2024).
  • Decline in femoral neck bone density over 1 year in healthy older adults.
  • Unknown long-term safety; FDA found bulk material poorly characterized.

Report side effects of any drug or product to the FDA through MedWatch. For a possible poisoning in the US, call Poison Control at 1-800-222-1222.

History

Synthesized by Merck in 1995; Merck stopped development in 1999. Lumos Pharma later licensed it as LUM-201 for pediatric growth hormone deficiency (phase 2). FDA placed it in 503B Category 2 (Dec 2022) and 503A Category 2 (Sept 2023).

Common questions

Is MK-677 an approved drug?

No. Merck stopped developing it in 1999, and a version called LUM-201 is still investigational for children with growth hormone deficiency 1. It is a pill, not a peptide 1.

What does the research show?

In a 12-month trial of 563 people with Alzheimer's disease, it gave no benefit on thinking or daily function 1. In healthy older adults, lean body mass rose 1.1 kg over a year, but hip bone density fell 1.

What doses were studied?

Adult trials used 25 mg by mouth once daily for 8 weeks to 12 months, and a children's trial used 0.4 or 0.8 mg/kg per day 1. These are research doses from FDA's 2024 review of the literature; MK-677 is not approved at any dose 1.

Is MK-677 safe?

A hip-fracture trial was stopped early when heart failure occurred in 6.5% of patients vs 1.7% on placebo, and FDA lists heart failure as its main safety concern 13. FDA advisers also cited fluid retention and high blood sugar 2.

Can pharmacies compound or sell MK-677?

FDA advisers voted 1 to 13 in October 2024 against adding it to the list pharmacies may compound from 2. It remains in FDA's Category 2 safety-risk group under both 503A and 503B 345. In August 2026 FDA warned online sellers that 'research use only' labels do not exempt products 7.

Is MK-677 banned in sport?

Yes. WADA prohibits it at all times and names ibutamoren among growth hormone secretagogues 6.

Related compounds

Growth hormone axisEarly human dataFlashcard

Ipamorelin

Ipamorelin acetate · NNC 26-0161

Ipamorelin is a small lab-made peptide (five building blocks) that copies the hunger hormone ghrelin to make the pituitary release growth hormone.

Growth hormone axisFDA-approvedFlashcard

Macimorelin

Macrilen · AEZS-130

Macimorelin is an oral ghrelin-like drug used as a one-time test for growth hormone deficiency in adults.

Growth hormone axisEarly human dataFlashcard

GHRP-2

Pralmorelin · KP-102

GHRP-2 is a small synthetic peptide that strongly triggers growth hormone release by acting on the ghrelin receptor.

Sources

  1. FDA briefing document, PCAC Oct 29, 2024: ibutamoren mesylate Regulatory
  2. FDA PCAC October 29, 2024 final summary minutes (ibutamoren, ipamorelin, kisspeptin-10, L-theanine votes) Regulatory
  3. FDA: Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks (content current as of 04/22/2026) Regulatory
  4. FDA: Bulk Drug Substances Nominated for Use in Compounding Under Section 503A (categories list, updated May 14, 2026) Regulatory
  5. FDA: Bulk Drug Substances Nominated for Use in Compounding Under Section 503B (categories list, updated March 21, 2025) Regulatory
  6. WADA 2026 Prohibited List (in force 1 January 2026) Regulatory
  7. Holland & Knight: Peptides at a Crossroads - HHS and FDA actions (Oct 2026) Regulatory

Last reviewed 2026-10-25 · How we research · Found an error? See our corrections policy.