The Pep Test Guide 2026
The Pep Test Guide 2026U.S. vendor guide
All compounds
HGH system

MK-677

Also known as: Ibutamors

Oral ghrelin receptor agonist. Increases IGF-1 in the long term. Non-peptide, Orally active.

MK-677

What is MK-677

MK-677 is an Oral active, non-peptidic ghrelin receptor agonist. Despite frequent classification in the peptide scene, MK-677 is chemically a small molecular compound, not a peptide. It acts on the same receptor as the body’s own ghrelin and triggers a release of growth hormone (GH) and insulin-like growth factor 1 (IGF-1).

MK-677 was originally developed by Merck (hence the MK prefix) in the 1990s as a potential therapy for age-related GH deficiency and sarcopenia. Clinical trials ran until phase 2/3, approval never took place. The drug was later licensed to Reverse Medical (now Lumos Pharma) and further developed under the name LUM-201 for pediatric growth disorders.

Chemical name: Ibutamors mesylate. CAS No: 159752-10-0. molecular weight: 624.8 g/mol. Important: MK-677 is not an anabolic and not a SARM, even if it often ends up in the same drawer.

Mechanism of action

Ghrelin is a gastric peptide that activates the GHSR-1a receptor (Growth Hormone Secretagogue Receptor). This activation in the hypothalamus and pituitary gland stimulates the pulsatile release of growth hormone. MK-677 mimics this effect, but is Orally bioavailable, which is not ghrelin itself.

GH levels typically increase within the first hour after taking them. IGF-1 is then produced via the liver. With prolonged use, IGF-1 levels increase by 40 to 90 percent compared to baseline, depending on the dose and individual.

In addition, MK-677 also activates the ghrelin receptor peripherally, which leads to classic ghrelin effects: increase in appetite, slight increase in cortisol and prolactin, as well as an influence on sleep architecture (more REM and deep sleep proportions in several studies).

Areas of application in research

  • Sarcopenia and age-related GH deficiency: Increase muscle mass and bone density in older adults
  • Pediatric growth disorders: Lumos Pharma develops LUM-201 for idiopathic short stature
  • Obesity and cachexia: Increase in appetite in chronic patients
  • Sleep architecture: Improvement of Deep Sleep Shares
  • Bone density: Studies in postmenopausal women with osteoporosis
  • Recovery after injury: GH-related regenerative effects

Study situation

The scientific basis is more solid than many other "research peptides" because MK-677 has been tested in regulated clinical trials.

Important works:

  • Murphy et al. (Journal of Clinical Endocrinology & Metabolism, 1998): One of the first studies on GH/IGF-1 increase in humans, dose-dependent effect detectable
  • Nass et al. (Annals of Internal Medicine, 2008): 12-month study in older adults, significant increase in fat-free mass, no effect on functional endpoints
  • Sigalos & Pastuszak (Sexual Medicine Reviews, 2018): Review on MK-677 and hormone effects
  • Adunsky et al. (Archives of Gerontology and Geriatrics, 2011): Study in hip fracture patients, mixed results

What is clear: MK-677 reliably increases GH and IGF-1. The fat-free mass increases. What remains unclear is whether these changes translate into functional improvements (strength, mobility, clinical outcomes). The wet study showed no clear advantage here. In addition, there are concerns about insulin resistance with prolonged use.

Mixing (reconstitution)

MK-677 is Orally active, therefore not classical mixing as with peptides. Typical pharmaceutical forms:

  • Powder weighed over fine balance (0,001 g resolution)
  • Solution in MCT oil, propylene glycol or ethanol
  • Prefabricated dropping solutions typically 10 or 25 mg/ml
  • Storage dark, cool, tightly sealed

In the case of own mixture of raw powder: accuracy is critical because the effective dose is in the milligram range.

Dosage range (research data)

Clinical studies used:

  • 10 mg daily (Nass et al., 12-month study)
  • 25 mg daily (often in the self-use community)
  • Up to 50 mg in individual studies, but without clear added value
  • Intake: once a day, in the evening preferred due to sleep effects
  • Cycle duration: continuously tested in studies up to 12 months

Due to a very long half-life, one dose per day is sufficient.

Side effects

From the clinical studies well documented:

  • Increased appetite (often, usually in the first month)
  • Water retention, slight oedema
  • Temporary lethargy and fatigue
  • Increased fasting blood sugar and reduced insulin sensitivity
  • Increase in cortisol and prolactin (clinically mostly not relevant)
  • Carpal tunnel-like symptoms at higher doses (GH effect)
  • Patients with heart failure potentially worsened symptoms (a study was therefore discontinued)

Theoretical risks: exacerbation of subclinical insulin resistance, possible promotion of hormone-sensitive tumors (caution when active disease).

Half-Life and Pharmacokinetics

Elimination half-life: around 4 to 6 hours, but GH/IGF-1 stimulation lasts 24 hours, so a daily dose is sufficient. Oral bioavailability is about 8 percent, which sounds low, but is sufficient because of the high potency and the GH pulse.

Metabolism via the liver (CYP3A4 involvement). Interactions with CYP3A4 inhibitors possible (ketoconazole, grapefruit juice theoretically relevant).

Steady-state after 2 to 3 days. Effect on IGF-1 shows measurable after 1 to 2 weeks, plateaued after 6 to 8 weeks.

Frequent questions

Is MK-677 a steroid? No. MK-677 is a ghrelin receptor agonist, not an anabolic steroid and not a SARM. It acts indirectly via the stimulation of the body’s own growth hormone.

How long a cycle? In studies, up to 12 months were continuously tested. In self-use typically 8 to 16 weeks, then rest, often due to water retention and appetite increase.

Do I have to watch for insulin resistance? Yes. With prolonged use MK-677 impairs the insulin sensitivity measurably. HbA1c and fasting blood sugar should be monitored, especially for prediabetes risk.

When do I take MK-677? Evening is common due to sleep effects and matching the natural GH peak at night. Some take it in the morning to avoid night effects.

Will I get hungry? Yes, the ghrelin effect significantly increases appetite, especially in the first 2 to 4 weeks. This is wanted in cachexia, undesirable in the cut.

Legal status U.S.

As of 2026: MK-677 has no pharmaceutical license in Germany, Austria and Switzerland. It is distributed in the research-use-only rail, which is a legal grey area.

WADA status: MK-677 is on the prohibited list, category S2 (peptide hormones, growth factors). For athletes under doping control clearly prohibited.

Own import: §73 AMG, not covered for therapy intention.

Related compounds

  • ipamoreline: peptidic ghrelin mimetic, injectable
  • GHRP-2 / GHRP-6Older ghrelin mimetics
  • CJC-1295GHRH analogue, often combined with ipamoreline
  • hexareline: Potent ghrelin mimetic, shorter application
  • tesamorelineGHRH analogue approved for HIV-related lipodystrophy

Note: All information is for research information only. These peptides are not approved as medicines in Germany. The contents do not replace medical advice. Application to humans is not legally covered in Germany.