New — Free Peptide Starter Guide (2026): 13 chapters, 34 cited studies

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Growth Hormone Peptides

MK-677 (Ibutamoren)

Also known as: Ibutamoren, Ibutamoren Mesylate, MK 677, L-163,191, Nutrobal

MK-677 (Ibutamoren) is an orally active, non-peptide ghrelin receptor agonist that increases growth hormone and IGF-1 levels. Unlike injectable GHRPs, it can be taken orally and has a 24-hour half-life, making it convenient for sustained GH optimization.

Half-Life

24 hours

Route

Oral

Category

Growth Hormone Peptides

Studies

50 references

Key Benefits

  • Increases lean muscle mass
  • Enhances bone density
  • Improves sleep quality and REM sleep
  • Accelerates recovery from training
  • Increases appetite
  • May improve skin elasticity and appearance
  • Supports fat loss while maintaining muscle
  • Oral administration — no injections required
  • 24-hour half-life allows once-daily dosing

Mechanism of Action

MK-677 is a selective, non-peptide agonist of the ghrelin receptor (GHSR-1a) and growth hormone secretagogue. It stimulates the pituitary gland to release growth hormone and increases IGF-1 levels without affecting cortisol. Its 24-hour half-life allows once-daily oral dosing. It amplifies the natural GH pulse, particularly during sleep, and increases GH pulsatility without blunting natural feedback mechanisms.

Dosing Protocols

Standard Protocol

Dose
10–25 mg
Frequency
Once daily
Timing
Before bedtime to coincide with nocturnal GH pulse
Cycle
8–12 weeks on, 4–8 weeks off

Start at lower doses (10 mg) to assess tolerance. Appetite increase and water retention are common initially and often subside. Taking before bed helps manage hunger increase during waking hours.

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Side Effects

  • Increased appetite (significant in some users)
  • Water retention and puffiness
  • Elevated blood glucose / insulin resistance (monitor in diabetics)
  • Lethargy initially
  • Numbness or tingling in extremities (carpal tunnel-like)
  • Possible prolactin elevation

Contraindications

Diabetes or blood sugar regulation issues (monitor closely). History of cancer. Competitive athletes (WADA banned). Edema or conditions affected by water retention.

Storage

Oral capsules/liquid: store at room temperature away from light and moisture.

Featured In Stacks

Anti-AgingIntermediate

Adult GH Deficiency & Hypopituitarism Support Protocol

A comprehensive growth hormone secretagogue protocol for adults with confirmed GH deficiency, hypopituitarism, or age-related somatopause. Restores the hypothalamic-pituitary GH axis through synergistic GHRH and ghrelin-receptor agonism, avoiding the risks of exogenous hGH administration.

Growth HormoneAdvanced

Advanced GH Pulse Optimization (GHRH+GHRP+MK-677)

The most comprehensive GH optimization protocol using two synergistic GHRH/GHRP pathways plus oral MK-677 for sustained baseline GH elevation. Produces physiological GH pulses without suppressing the natural GH axis.

Growth HormoneAdvanced

Advanced Growth Hormone Peptide Stack

The most comprehensive GH peptide stack available, layering a GHRH analog, a GHRP, and an oral GH secretagogue for synergistic 4-6x greater GH release than any single agent alone. Designed for body composition, fat loss, recovery, and anti-aging.

Fat LossIntermediate

Body Recomposition: Fat Loss + Lean Mass

Simultaneously reduce body fat and build lean muscle using complementary GH axis peptides and targeted lipolytic compounds. The gold standard body recomposition stack.

Clinical Research

50 studies
  1. 1.
    Knowing the minimal detectable dose can facilitate the interpretation of a hair test result: II. Case example with ibutamoren (MK-677), a growth hormone secretagogue

    Kintz P, Gheddar L · Clinica chimica acta; international journal of clinical chemistry · 2026PubMed Verified

  2. 2.
    Detection of the growth hormone secretagogue MK-0677 in equine hair following oral administration

    Viljanto M, Cutler C, Taylor P, Habershon-Butcher J, Gray B · Drug testing and analysis · 2023PubMed Verified

  3. 3.
    LGD-4033 and MK-677 use impacts body composition, circulating biomarkers, and skeletal muscle androgenic hormone and receptor content: A case report

    Cardaci TD, Machek SB, Wilburn DT, Heileson JL, Harris DR, Cintineo HP et al. · Experimental physiology · 2022Case ReportPubMed Verified

  4. 4.
    Characterization of growth hormone secretagogue small molecule ibutamoren (MK-0677) and its possible metabolites in thoroughbred horses for doping control

    Philip M, Karakka Kal AK, Subhahar MB, Karatt TK, Mathew B, Koshy SA · Rapid communications in mass spectrometry : RCM · 2022PubMed Verified

  5. 5.
    Equine metabolism of the growth hormone secretagogue MK-0677 in vitro and in urine and plasma following oral administration

    Cutler C, Viljanto M, Taylor P, Habershon-Butcher J, Van Eenoo P · Drug testing and analysis · 2022PubMed Verified

  6. 6.
    Characterization of equine liver microsome-generated metabolites of growth hormone secretagogue small molecule ibutamoren

    Philip M, Karakka Kal AK, Subhahar MB, Perwad Z, Karatt TK · Rapid communications in mass spectrometry : RCM · 2021PubMed Verified

  7. 7.
    Skin Acceleration Levels Estimated by a Neck-surface Accelerometer during Phonation Are Affected by The Mechanical Properties of The Anterior Cervical Skin

    Umatani M, Ogawa M, Hosokawa K, Kato C, Okajima E, Iwahashi T et al. · Journal of voice : official journal of the Voice Foundation · 2023PubMed Verified

  8. 8.
    Brain and kidney GHS-R1a underexpression is associated with changes in renal function and hemodynamics during neurogenic hypertension

    Sales da Silva E, Ferreira PM, Castro CH, Pacheco LF, Graziani D, Pontes CNR et al. · Molecular and cellular endocrinology · 2020PubMed Verified

  9. 9.
    MK0677, a Ghrelin Mimetic, Improves Neurogenesis but Fails to Prevent Hippocampal Lesions in a Mouse Model of Alzheimer's Disease Pathology

    Tian J, Wang T, Wang Q, Guo L, Du H · Journal of Alzheimer's disease : JAD · 2019PubMed Verified

  10. 10.
    Effect of the Orally Active Growth Hormone Secretagogue MK-677 on Somatic Growth in Rats

    Lee J, Kwon A, Chae HW, Lee WJ, Kim TH, Kim HS · Yonsei medical journal · 2018PubMed Verified

  11. 11.
    MK-0677, a Ghrelin Agonist, Alleviates Amyloid Beta-Related Pathology in 5XFAD Mice, an Animal Model of Alzheimer's Disease

    Jeong YO, Shin SJ, Park JY, Ku BK, Song JS, Kim JJ et al. · International journal of molecular sciences · 2018PubMed Verified

  12. 12.
    The Safety and Efficacy of Growth Hormone Secretagogues

    Sigalos JT, Pastuszak AW · Sexual medicine reviews · 2018ReviewPubMed Verified

  13. 13.
    Oral ghrelin receptor agonist MK-0677 increases serum insulin-like growth factor 1 in hemodialysis patients: a randomized blinded study

    Campbell GA, Patrie JT, Gaylinn BD, Thorner MO, Bolton WK · Nephrology, dialysis, transplantation : official publication of the European Dialysis and Transplant Association - European Renal Association · 2018RCTPubMed Verified

  14. 14.
    Central Ghrelin Resistance Permits the Overconsolidation of Fear Memory

    Harmatz ES, Stone L, Lim SH, Lee G, McGrath A, Gisabella B et al. · Biological psychiatry · 2017PubMed Verified

  15. 15.
    Thyroid hormone modulates food intake and glycemia via ghrelin secretion in Zucker fatty rats

    Patel K, Joharapurkar A, Dhanesha N, Patel V, Kshirsagar S, Raval P et al. · Drug research · 2014PubMed Verified

  16. 16.
    Semagacestat, a γ-secretase inhibitor, activates the growth hormone secretagogue (GHS-R1a) receptor

    Schellekens H, McNamara O, Dinan TG, McCarthy JV, McGlacken GP, Cryan JF · The Journal of pharmacy and pharmacology · 2013PubMed Verified

  17. 17.
    MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture: a multicenter, randomized, placebo-controlled phase IIb study

    Adunsky A, Chandler J, Heyden N, Lutkiewicz J, Scott BB, Berd Y et al. · Archives of gerontology and geriatrics · 2011RCTPubMed Verified

  18. 18.
    Update on new therapeutic options for the somatopause

    Ceda GP, Dall'Aglio E, Morganti S, Denti L, Maggio M, Lauretani F et al. · Acta bio-medica : Atenei Parmensis · 2010ReviewPubMed Verified

  19. 19.
    Anabolic interventions in ESRD: light at the end of the tunnel?

    Hakim RM, Ikizler TA · American journal of kidney diseases : the official journal of the National Kidney Foundation · 2009PubMed Verified

  20. 20.
    Rejuvenation in older adults receiving oral ghrelin

    Webster J · Annals of internal medicine · 2009PubMed Verified

  21. 21.
    Rejuvenation in older adults receiving oral ghrelin

    Gaugg M · Annals of internal medicine · 2009PubMed Verified

  22. 22.
    Rejuvenation in older adults receiving oral ghrelin

    Rafael H · Annals of internal medicine · 2009PubMed Verified

  23. 23.
    Sarcopenia and the elusive fountain of youth

    Hanauer SB · Nature clinical practice. Gastroenterology & hepatology · 2009PubMed Verified

  24. 24.
    Growth hormone secretagogue MK-677: no clinical effect on AD progression in a randomized trial

    Sevigny JJ, Ryan JM, van Dyck CH, Peng Y, Lines CR, Nessly ML et al. · Neurology · 2008RCTPubMed Verified

  25. 25.
    Use of growth hormone secretagogues to prevent or treat the effects of aging: not yet ready for prime time

    Blackman MR · Annals of internal medicine · 2008PubMed Verified

  26. 26.
    Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial

    Nass R, Pezzoli SS, Oliveri MC, Patrie JT, Harrell FE Jr, Clasey JL et al. · Annals of internal medicine · 2008RCTPubMed Verified

  27. 27.
    Summaries for patients. Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults

    Annals of internal medicine · 2008PubMed Verified

  28. 28.
    Overlapping binding site for the endogenous agonist, small-molecule agonists, and ago-allosteric modulators on the ghrelin receptor

    Holst B, Frimurer TM, Mokrosinski J, Halkjaer T, Cullberg KB, Underwood CR et al. · Molecular pharmacology · 2009PubMed Verified

  29. 29.
    The effects of growth hormone and insulin-like growth factor-1 on the aging cardiovascular system and its progenitor cells

    Devin JK, Young PP · Current opinion in investigational drugs (London, England : 2000) · 2008ReviewPubMed Verified

  30. 30.
    (D)-2-tert-Butoxycarbonylamino-5,5-difluoro-5-phenyl-pentanoic acid: synthesis and incorporation into the growth hormone secretagogues

    Li J, Chen SY, Murphy BJ, Flynn N, Seethala R, Slusarchyk D et al. · Bioorganic & medicinal chemistry letters · 2008PubMed Verified

  31. 31.
    Growth hormone and insulin-like growth factor-I as an endocrine axis in Alzheimer's disease

    Gómez JM · Endocrine, metabolic & immune disorders drug targets · 2008ReviewPubMed Verified

  32. 32.
    Ghrelin receptor (GHS-R1A) agonists show potential as interventive agents during aging

    Smith RG, Sun Y, Jiang H, Albarran-Zeckler R, Timchenko N · Annals of the New York Academy of Sciences · 2007ReviewPubMed Verified

  33. 33.
    Highly potent growth hormone secretagogues

    Lu Z, Tata JR, Cheng K, Wei L, Chan WW, Butler B et al. · Bioorganic & medicinal chemistry letters · 2007PubMed Verified

  34. 34.
    Gateways to clinical trials

    Bayes M, Rabasseda X, Prous JR · Methods and findings in experimental and clinical pharmacology · 2006PubMed Verified

  35. 35.
    Impurity profile tracking for active pharmaceutical ingredients: case reports

    Zhou L, Mao B, Reamer R, Novak T, Ge Z · Journal of pharmaceutical and biomedical analysis · 2007PubMed Verified

  36. 36.
    Nonpeptide and peptide growth hormone secretagogues act both as ghrelin receptor agonist and as positive or negative allosteric modulators of ghrelin signaling

    Holst B, Brandt E, Bach A, Heding A, Schwartz TW · Molecular endocrinology (Baltimore, Md.) · 2005PubMed Verified

  37. 37.
    Development of growth hormone secretagogues

    Smith RG · Endocrine reviews · 2005ReviewPubMed Verified

  38. 38.
    Ghrelin and des-acyl ghrelin both inhibit isoproterenol-induced lipolysis in rat adipocytes via a non-type 1a growth hormone secretagogue receptor

    Muccioli G, Pons N, Ghè C, Catapano F, Granata R, Ghigo E · European journal of pharmacology · 2004PubMed Verified

  39. 39.
    The effects of MK-0677, an oral growth hormone secretagogue, in patients with hip fracture

    Bach MA, Rockwood K, Zetterberg C, Thamsborg G, Hébert R, Devogelaer JP et al. · Journal of the American Geriatrics Society · 2004RCTPubMed Verified

  40. 40.
    Effect of ghrelin and synthetic growth hormone secretagogues in normal and ischemic rat heart

    Frascarelli S, Ghelardoni S, Ronca-Testoni S, Zucchi R · Basic research in cardiology · 2003PubMed Verified

  41. 41.
    The effect of treatment with the oral growth hormone (GH) secretagogue MK-677 on GH isoforms

    Svensson J, Boguszewski CL, Shibata F, Carlsson B, Carlsson LM, Bengtsson BA · Growth hormone & IGF research : official journal of the Growth Hormone Research Society and the International IGF Research Society · 2003RCTPubMed Verified

  42. 42.
    Pyrazolinone-piperidine dipeptide growth hormone secretagogues (GHSs). Discovery of capromorelin

    Carpino PA, Lefker BA, Toler SM, Pan LC, Hadcock JR, Cook ER et al. · Bioorganic & medicinal chemistry · 2003PubMed Verified

  43. 43.
    Ghrelin: endocrine and non-endocrine actions

    Broglio F, Arvat E, Benso A, Papotti M, Muccioli G, Deghenghi R et al. · Journal of pediatric endocrinology & metabolism : JPEM · 2002ReviewPubMed Verified

  44. 44.
    Ghrelin and des-acyl ghrelin inhibit cell death in cardiomyocytes and endothelial cells through ERK1/2 and PI 3-kinase/AKT

    Baldanzi G, Filigheddu N, Cutrupi S, Catapano F, Bonissoni S, Fubini A et al. · The Journal of cell biology · 2002PubMed Verified

  45. 45.
    The antiproliferative effect of synthetic peptidyl GH secretagogues in human CALU-1 lung carcinoma cells

    Ghè C, Cassoni P, Catapano F, Marrocco T, Deghenghi R, Ghigo E et al. · Endocrinology · 2002PubMed Verified

  46. 46.
    Spiro(indoline-3,4'-piperidine) growth hormone secretagogues as ghrelin mimetics

    Palucki BL, Feighner SD, Pong S, McKee KK, Hreniuk DL, Tan C et al. · Bioorganic & medicinal chemistry letters · 2001PubMed Verified

  47. 47.
    Highly potent growth hormone secretagogues: hybrids of NN703 and ipamorelin

    Hansen TK, Ankersen M, Raun K, Hansen BS · Bioorganic & medicinal chemistry letters · 2001PubMed Verified

  48. 48.
    Effects of oral administration of ibutamoren mesylate, a nonpeptide growth hormone secretagogue, on the growth hormone-insulin-like growth factor I axis in growth hormone-deficient children

    Codner E, Cassorla F, Tiulpakov AN, Mericq MV, Avila A, Pescovitz OH et al. · Clinical pharmacology and therapeutics · 2001RCTPubMed Verified

  49. 49.
    Growth hormone secretagogue receptor family members and ligands

    Smith RG, Leonard R, Bailey AR, Palyha O, Feighner S, Tan C et al. · Endocrine · 2001ReviewPubMed Verified

  50. 50.
    Effects of growth hormone and its secretagogues on bone

    Svensson J, Lall S, Dickson SL, Bengtsson BA, Rømer J, Ahnfelt-Rønne I et al. · Endocrine · 2001ReviewPubMed Verified

Medical disclaimer: This information is for educational purposes only and does not constitute medical advice. Many compounds listed are research chemicals not approved for human use. Always consult a qualified healthcare professional before starting any protocol.

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