MK‑677 (Ibutamoren)
Orally active non-peptide ghrelin receptor (GHSR-1a) agonist that raises the amplitude of pituitary GH pulses and thereby plasma IGF-1. Developed by Merck, never approved. NOT a SARM. The longest human dataset is the two-year Nass 2008 RCT in 65 older adults.
The links above are labelled third-party affiliate links. MolekulaX does not sell and does not verify product quality.
WHAT IS MK-677 (IBUTAMOREN)?
Detailed overview
MK-677 (ibutamoren, ibutamoren mesylate) is an orally active, non-peptide agonist of the ghrelin receptor (GHSR-1a). It acts at the hypothalamus and pituitary: it increases the amplitude of growth hormone pulses and thereby raises plasma IGF-1, while largely preserving the physiological pulsatile pattern. That last point is the meaningful difference from exogenous growth hormone, where continuous levels suppress endogenous secretion. It is worth stating clearly what this is NOT: MK-677 is not a selective androgen receptor modulator. It does not bind the androgen receptor, does not suppress the hypothalamic-pituitary-testicular axis, and requires no post-cycle therapy. Its placement next to SARMs comes from shop categorisation, not pharmacology. The human evidence rests on four studies. Murphy 1998 showed in a short caloric-restriction model that the compound reverses diet-induced nitrogen loss. Murphy 1999 demonstrated raised bone-turnover markers in older adults. Most important is Nass 2008, a two-year placebo-controlled trial in 65 healthy older adults: at 25 mg daily, GH and IGF-1 returned to the young-adult range and fat-free mass rose by roughly 1.1 kg, BUT fasting glucose and insulin resistance worsened, and that worsening did not resolve during the trial. Sevigny 2008 found no clinical benefit in 563 Alzheimer patients; that trial is chiefly valuable as a safety database. The overall picture: a real, measurable body-composition effect whose price is deteriorating carbohydrate metabolism. For anyone using it, glucose monitoring is not optional but a condition of use.
Mechanism
Non-peptide ghrelin receptor (GHSR-1a) agonist; raises GH pulse amplitude and IGF-1.
Body composition (Nass 2008)
About +1.1 kg fat-free mass at 25 mg/day over 2 years in older adults.
Critical adverse effect
Worsening insulin sensitivity and rising fasting glucose that did not resolve during the trial.
Half-life
~4-6 h, but the IGF-1 elevation is sustained, so once-daily dosing suffices.
Legal status
Never approved. WADA-banned (S2, GH secretagogues).
Data console
Lab data
Safety
Side effects, stop signs, contraindications
Side effects · 6
- Marked appetite increase: the direct, expected consequence of ghrelin receptor agonism. For many this is the strongest noticeable effect, and a serious drawback during a cutting phase.
- Worsening insulin sensitivity and rising fasting glucose: in the two-year Nass 2008 trial this was the most significant metabolic adverse effect, and it did not resolve during treatment.
- Water retention and peripheral edema: a classic accompaniment of GH axis activation, typically most pronounced in the first weeks.
- Carpal-tunnel-like complaints: numbness and paraesthesia in the hand from soft-tissue swelling, usually easing on dose reduction.
- Lethargy and daytime drowsiness, especially in the introductory phase; many therefore switch to evening dosing.
- Mild prolactin and cortisol elevation: usually clinically insignificant, but worth measuring if symptoms appear.
Contraindications · 5
- Diabetes, prediabetes or insulin resistance: MK-677 documentedly worsens glucose metabolism, an absolute contraindication.
- Active or treated malignancy: elevated IGF-1 carries a theoretical proliferative risk, avoid without oncology consultation.
- Heart failure or untreated hypertension: fluid retention places further load on the circulation.
- Pregnancy and breastfeeding: no safety data, use is prohibited.
- Competitive sport under testing: WADA bans GH secretagogues (S2), with the same sanction as growth hormone itself.
Related Performance Compounds
Same therapeutic category
Studies
Related research and clinical findings
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
MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism.
Murphy MG, Plunkett LM, Gertz BJ
Oral administration of the growth hormone secretagogue MK-677 increases markers of bone turnover in healthy and functionally impaired elderly adults. The MK-677 Study Group.
Murphy MG, Bach MA, Plotkin D
Growth hormone secretagogue MK-677: no clinical effect on AD progression in a randomized trial.
Sevigny JJ, Ryan JM, van Dyck CH
Telegram
Have a question about MK‑677 (Ibutamoren)?
Reach out to an advisor on Telegram. Performance compounds are presented with a harm-reduction approach, based on peer-reviewed evidence.
Personalized consultation
Want a detailed conversation tailored to your data?
Fill out the prep intake form (your goals, training and health data), and the advisor prepares from it to give genuinely personalized guidance.
Fill out the form~5–7 min · prep questionnaire · confidential · GDPR-compliant
The information here is for educational and scientific purposes only. Performance-enhancing compounds (AAS, prohormones, stimulants, doping agents) are illegal without prescription in Hungary and most of the EU, and carry serious health and legal risks. WADA bans them in competitive sport. This is NOT a usage guide, and we do not encourage any illegal use. If you do use them, medical supervision and regular bloodwork are ESSENTIAL. Severe endocrine, cardiovascular, hepatic and psychiatric side effects are possible.