MK-677
An orally active growth hormone secretagogue that mimics ghrelin to stimulate GH and IGF-1 release.
What is MK-677?
MK-677 (Ibutamoren) is a non-peptide, orally active growth hormone secretagogue. While technically not a peptide, it is commonly discussed alongside peptides because it acts on the same ghrelin receptor (GHS-R1a) as peptide secretagogues like Ipamorelin. Its oral bioavailability makes it unique in the GH-optimization space.
What MK-677 Is Investigated For
MK-677 (ibutamoren) is a non-peptide, orally active ghrelin receptor agonist investigated for GH/IGF-1 elevation, body composition improvement, sleep quality, and muscle preservation — its oral bioavailability being its main practical differentiator from injectable peptide secretagogues like ipamorelin. The strongest evidence comes from Merck's substantial 1990s–2000s clinical program: the 2008 Nass 2-year RCT (n=65, healthy older adults) established sustained IGF-1 elevation and a ~1.6 kg fat-free mass gain, and multiple shorter trials showed 40–90% IGF-1 elevation, increased REM and stage IV sleep, and ghrelin-mediated appetite increase. The honest caveats are substantial: Merck's program never produced an approved indication (Alzheimer's trial failed, the CHF trial was halted early due to increased mortality in the MK-677 arm, and functional-performance benefits in elderly populations did not meet the regulatory bar despite body-composition changes). Glucose tolerance and insulin sensitivity reliably worsen with sustained use — this is the clearest duration-related safety signal. MK-677 is not FDA-approved, it is not a peptide (it is a small-molecule spiropiperidine metabolized by CYP3A4 with the associated drug-interaction profile), and the 'SARM' and 'oral HGH' framings common in research-chemical marketing are both wrong.
History & Discovery
MK-677 (ibutamoren, also coded MK-0677) was discovered and developed by Merck Research Laboratories in the mid-1990s, emerging from a medicinal-chemistry program aimed at finding orally bioavailable mimetics of the peptide GH secretagogues (GHRP-6, GHRP-2) that had previously demonstrated potent GH release but required injection. Merck chemists identified a non-peptide spiropiperidine scaffold that retained high-affinity agonism at the ghrelin receptor (GHS-R1a) — this structural class is important because it means MK-677, despite being grouped with peptide secretagogues functionally, is not itself a peptide. It is a small-molecule drug. Merck progressed MK-677 through a substantial clinical development program in the late 1990s and 2000s across multiple indications: frail elderly adults, hip-fracture recovery, growth hormone-deficient adults, pediatric GH deficiency, Alzheimer's disease, and obesity. The 2008 Nass et al. trial (a 2-year RCT in healthy older adults, n=65) remains the most-cited long-duration human dataset for the compound. Despite replicable increases in GH and IGF-1 across trials, Merck ultimately did not secure approval for any indication — the Alzheimer's trial failed, and the modest functional-performance outcomes in the elderly trials did not meet the bar for regulatory approval despite measurable body-composition effects. Development was effectively discontinued. A decade later, MK-677 was relicensed to Ammonett Pharma, which has pursued pediatric GH deficiency indications, but no approval has resulted as of 2026. MK-677 entered the 'research chemical' and performance-enhancement markets in the 2010s and is now one of the most widely sold non-approved GH-axis compounds online. It is frequently discussed alongside peptide secretagogues (ipamorelin, CJC-1295) because of its shared mechanism and overlapping use cases — though its oral bioavailability, long half-life (~24 hours), and non-peptide structure make it pharmacologically distinct.
How It Works
MK-677 mimics ghrelin, the hunger hormone, by activating the same receptor. This triggers the pituitary gland to release growth hormone. Unlike injectable peptides, it can be taken orally, which is its main practical advantage.
MK-677 is a non-peptide spiropiperidine that acts as a potent, long-acting, orally active agonist of the GHS-R1a receptor. It increases GH secretion by mimicking the GH-stimulating action of endogenous ghrelin. It produces sustained increases in IGF-1 levels without affecting cortisol. However, it also activates ghrelin's orexigenic (appetite-stimulating) pathways and can affect glucose homeostasis through GH-mediated insulin resistance.
Evidence Snapshot
Human Clinical Evidence
Moderate to strong. Multiple human studies demonstrating GH and IGF-1 elevation, body composition effects, and sleep improvement.
Animal / Preclinical
Strong. Well-characterized pharmacology.
Mechanistic Rationale
Strong. GHS-R1a receptor pharmacology is well understood.
Research Gaps & Open Questions
What the current literature has not yet settled about MK-677:
- 01Long-term (>2 year) human safety beyond the 2008 Nass trial is not characterized; use extending for years — which is common in wellness and performance settings — has no published long-term pharmacovigilance data.
- 02Carcinogenicity — the sustained IGF-1 elevation over years raises a theoretical tumor-promotion concern that has not been resolved by dedicated long-duration human studies.
- 03Glucose-tolerance trajectory beyond 2 years is unknown; whether the insulin-resistance effect plateaus, progresses to overt diabetes, or reverses with continued exposure has not been studied.
- 04Whether cycled dosing (e.g., 12 weeks on, 4 off) actually reduces cumulative metabolic harm vs. continuous dosing has not been tested head-to-head.
- 05The 2008 trial's lack of functional-performance benefit despite lean-mass gain raises an unresolved question: does the body-composition effect translate to meaningful real-world outcomes in healthy aging, or is it a cosmetic endpoint?
- 06Cardiovascular safety signal from the CHF trial (increased mortality in MK-677 arm) has not been fully mechanistically explained — whether this represents a risk in broader populations is unclear.
- 07Pediatric long-term safety in GH-deficient children has limited data; the Ammonett program is active but results remain pending.
Forms & Administration
MK-677 is taken orally, typically once daily. This is its primary advantage over injectable GH secretagogues. Protocols should be determined by a qualified clinician with metabolic monitoring.
Dosing & Protocols
The ranges below reflect protocols commonly discussed in the literature and by clinicians — not a prescription. Actual dosing for any individual should be determined by a qualified healthcare provider who knows the patient.
Typical Range
Published human trials have used MK-677 in the 10–25 mg oral daily range, with 25 mg once daily being the dose used in the 2008 Nass 2-year RCT and most long-duration body-composition work. Commonly referenced wellness and performance protocols use 10–25 mg once daily, with 12.5 mg frequently cited as a compromise between efficacy and side-effect tolerability (appetite increase, water retention, glycemic effects scale with dose).
Frequency
Once-daily dosing is sufficient because the half-life is approximately 24 hours — steady-state plasma levels are achieved within about a week of daily dosing. Evening or bedtime administration is most commonly discussed, for two reasons: it aligns with the natural nocturnal GH pulse and can enhance slow-wave sleep; and it pushes peak appetite stimulation into overnight hours rather than during the day. Some users split the dose (morning + evening) to smooth plasma levels and reduce peak-trough appetite swings, but this offers no clear pharmacokinetic advantage. Unlike the peptide GHRPs, MK-677 does not stack synergistically with GHRH analogs the way ipamorelin does — the dual-pathway rationale still applies pharmacologically, but the oral/injectable mismatch and long half-life mean MK-677 is typically used as a standalone rather than in a CJC-1295 stack.
Timing Considerations
Time of day
Bedtime is the most common window to align with the nocturnal GH pulse, but MK-677's ~24-hour half-life means clock time matters less than with injectable GHRPs — consistency day-to-day matters more than the specific hour.
Relative to meals
With or without food. Some users report less next-morning grogginess or appetite-driven sleep disruption when dosed with a small protein-containing snack; others prefer a fully fasted dose.
Relative to exercise
Not tied to training. MK-677 is a daily chronic dosing drug, so workout timing doesn't meaningfully shape the pharmacokinetics.
Cycle Length
Cycling is more commonly discussed for MK-677 than for the injectable secretagogues, precisely because its sustained (non-pulsatile) receptor occupancy raises more concern about pituitary desensitization and chronic metabolic adaptation. Typical protocols run 8–16 weeks on, followed by 4+ weeks off. Continuous multi-year use has been studied in the 2008 Nass trial without evidence of tachyphylaxis, but glucose tolerance and insulin sensitivity do show progressive deterioration over time — meaning 'the GH/IGF-1 effect is sustained' does not mean 'the metabolic cost stays flat.' For users with any baseline insulin resistance, shorter cycles are a prudent precaution.
Protocol Notes
MK-677 is an oral compound, supplied as capsules, tablets, or oral solution. Because it is not a peptide, it does not require reconstitution with bacteriostatic water and does not need to be injected. Oral bioavailability is approximately 30–60% depending on formulation and fed/fasted state. Most protocols call for taking it on an empty stomach or at bedtime to maximize the GH pulse (elevated insulin and circulating amino acids from a recent meal blunt GH response), though food does not meaningfully block the downstream IGF-1 elevation over days of steady-state dosing. Purity and dosing accuracy of research-chemical MK-677 vary substantially — third-party assay data has repeatedly shown underdosing and occasional cross-contamination in online-sourced product. This quality variance is a material safety concern independent of the pharmacology.
MK-677 is not FDA-approved for any indication. It is sold in the US exclusively as a research chemical labeled 'not for human consumption,' which is not an authorized channel for human use. The numbers above describe commonly-referenced protocols, not a prescription.
Timeline of Effects
Onset
Appetite increase is typically the first noticeable effect, often within 1–3 days of starting dosing — a direct consequence of ghrelin-receptor agonism and independent of the downstream GH/IGF-1 axis. Sleep changes (deeper slow-wave sleep, more REM) follow in the first 1–2 weeks. Body-composition changes (lean mass gain, modest fat-mass reduction) require 4–8+ weeks of consistent use before becoming visible. Water retention and mild extremity puffiness can appear within the first 2 weeks.
Peak Effect
Serum IGF-1 rises progressively over the first 4–8 weeks and plateaus at levels typically 40–90% above baseline (depending on dose and baseline). Body-composition benefits plateau around 3 months in the published literature. Continuous use beyond 6 months shows stable or slowly declining efficacy on subjective markers even as IGF-1 levels remain elevated — a pattern that some users describe as 'blunting' or tachyphylaxis, though whether this is true receptor desensitization or a ceiling effect on the downstream remodeling is unclear. Glucose tolerance tends to worsen progressively with continuous use — this is the clearest dose-duration-related side effect.
After Discontinuation
Endogenous GH pulsatility and ghrelin tone return to baseline within days. IGF-1 returns to pre-treatment levels over 2–4 weeks. Appetite normalizes quickly — often within 3–7 days. Any accumulated lean mass or fat-loss benefits wane over weeks to months depending on training, nutrition, and age. No HPG-axis suppression and no post-cycle therapy requirement. Insulin sensitivity generally recovers over 4–12 weeks off; users with baseline metabolic dysfunction may take longer to renormalize.
Monitoring & Measurement
Bloodwork & Labs
- •IGF-1 (serum) — reliably rises 40–80% within 4–8 weeks
- •Fasting glucose and HbA1c — this is the dose-limiting side effect for most users
- •Fasting insulin (HOMA-IR) — MK-677 produces insulin resistance before fasting glucose climbs, so insulin rises first
- •Lipid panel
- •Cortisol and prolactin — expected to remain within reference range at typical doses; a meaningful rise warrants attention
Functional & Performance Tests
- •DEXA scan — lean mass is the headline endpoint, and MK-677 drives the largest lean-mass gain of any oral secretagogue
- •Waist circumference
- •Grip strength
- •Ankle or pretibial edema check (pinch the skin at the tibia and look for indentation) — water retention is common in the first 2 weeks
- •Overnight sleep quality via wearable
When to Test
Baseline, 6 weeks, and 12 weeks. If you're insulin-resistant at baseline, add a glucose and insulin check at 2–4 weeks.
Interpretation & Notes
MK-677 reliably lifts IGF-1 by 40–80% within 4–8 weeks and produces the largest lean-mass response of any oral secretagogue. The dose-limiting issue in most users isn't lack of effect — it's glycemic drift. Fasting glucose and HbA1c both tend to rise; if fasting glucose exceeds 110 mg/dL or HbA1c crosses 5.7, pull the dose back or discontinue. Water retention typically settles within 2 weeks; if ankle edema persists, the dose is likely too high. Unlike injectable peptides, MK-677 has drug-like small-molecule pharmacokinetics — interactions with CYP3A4 substrates and hepatic first-pass metabolism make it behave more like a pharmaceutical than a peptide. Labs available direct-to-consumer via LabCorp, Quest, Marek Health, and Ulta Lab Tests; interpret with a clinician, especially the insulin-resistance workup.
Common Questions
Who MK-677 Is NOT For
- •Active or recent-history cancer — GH and IGF-1 elevation may accelerate proliferation of existing malignancies; chronic IGF-1 elevation is a particular concern given MK-677's sustained dosing profile.
- •Pregnancy — no human pregnancy safety data; reproductive-toxicology characterization is absent.
- •Breastfeeding — no data on transfer into breast milk or effects on nursing infants.
- •Type 2 diabetes or significant insulin resistance — MK-677 reliably worsens glucose tolerance and insulin sensitivity; this is its most clinically relevant metabolic effect and is more pronounced than with injectable secretagogues.
- •Prediabetes or metabolic syndrome — same rationale; at minimum, use requires monitoring of HbA1c, fasting glucose, and insulin.
- •Pediatric use outside a diagnosed GH deficiency managed by a pediatric endocrinologist.
- •Active acromegaly or pituitary adenoma — further stimulation of GH-producing cells is contraindicated.
- •Congestive heart failure — the Merck trial in CHF patients was halted early due to increased mortality in the MK-677 arm, making this a specific and documented contraindication.
- •Uncontrolled hypertension or moderate-to-severe sleep apnea — GH-mediated fluid retention and upper-airway effects can worsen both.
- •Known hypersensitivity to spiropiperidine compounds or excipients.
Drug & Supplement Interactions
MK-677 has more documented interaction data than the peptide secretagogues because it went through a substantial Merck clinical program. Because it is a small-molecule compound metabolized hepatically, CYP450-mediated interactions apply that do not apply to peptide secretagogues. CYP3A4 is the primary metabolic pathway. Strong CYP3A4 inhibitors (ketoconazole, clarithromycin, ritonavir, grapefruit juice in large quantities) can substantially increase MK-677 exposure; strong inducers (rifampin, phenytoin, carbamazepine, St. John's Wort) can reduce it. Dose adjustment is theoretically warranted with co-administered CYP3A4 modulators, though no formal dose-adjustment guidance exists outside clinical-trial protocols. Glucose-regulating medications are the most clinically relevant interaction. Insulin, sulfonylureas, GLP-1 agonists, and SGLT2 inhibitors interact with MK-677's GH-mediated worsening of insulin sensitivity — patients on these agents may see elevated HbA1c and fasting glucose that require dose adjustment over weeks. Corticosteroids blunt somatotroph response and attenuate MK-677's GH effect. Somatostatin analogs (octreotide, lanreotide) pharmacologically antagonize it. Opioids and SSRIs have more documented ghrelin-pathway interactions with MK-677 than with injectable GHRPs — chronic opioid exposure can alter ghrelin tone, and serotonergic agents have been shown in preclinical work to modulate GHS-R signaling. Clinical significance is not precisely quantified. Oral estrogens reduce hepatic IGF-1 generation and can blunt the apparent IGF-1 response to MK-677 in labs. Any concurrent medications should be disclosed to the prescribing clinician.
Safety Profile
Common Side Effects
Cautions
- • May worsen insulin resistance
- • Not appropriate for diabetics without careful monitoring
- • Can significantly increase appetite
- • May elevate prolactin in some individuals
What We Don't Know
Long-term metabolic effects, particularly on insulin sensitivity, require further study. It has not received FDA approval.
Legal Status
United States
MK-677 is not FDA-approved for any indication and is not a controlled substance at the federal level. It has historically been sold in the US as a 'research chemical' labeled not for human consumption — not an authorized channel for human use — and the FDA has issued warning letters to companies marketing it as a dietary supplement. Its regulatory status shifted in April 2026: on April 15, HHS Secretary Kennedy directed the FDA to remove MK-677 from Category 2 (bulk drug substances presenting significant safety risks), effective April 22, 2026. MK-677 is in the second PCAC review cohort scheduled for completion by end of February 2027 (alongside Cathelicidin LL-37, Dihexa acetate, injectable GHK-Cu, and Melanotan II). Removal from Category 2 is not authorization to compound, and the PCAC previously voted against MK-677 for the 503A Bulks List on cardiac-safety grounds — so reinstatement is not assured. Marketing MK-677 for human use remains legally precarious pending the February 2027 PCAC decision.
International
The European Medicines Agency and UK MHRA have not authorized MK-677. Australia's TGA classifies it as a prohibited substance (Schedule 10) when sold for human use. The UK has included MK-677 under general consumer safety enforcement. Canada treats it as an unapproved drug. Several jurisdictions have pursued enforcement against online sellers marketing it as a supplement.
Sports & Competition
MK-677 is explicitly prohibited under WADA's S2 category (Peptide Hormones, Growth Factors, Related Substances and Mimetics) — although MK-677 is not a peptide, the S2 category explicitly covers 'ghrelin receptor agonists' and 'growth hormone secretagogues,' which catches MK-677 directly. Prohibited at all times, in and out of competition. LC-MS/MS detection in urine is well-established and can identify use for at least several days after discontinuation. Athletes subject to WADA code must avoid it.
Regulatory status changes over time. Verify current local rules with a qualified professional.
Myths & Misconceptions
Myth
MK-677 is a peptide.
Reality
It is not. MK-677 is a non-peptide small-molecule spiropiperidine. It is grouped with peptide secretagogues because it acts at the same ghrelin receptor (GHS-R1a), but structurally and pharmacokinetically it is a conventional small-molecule drug — orally bioavailable, hepatically metabolized via CYP3A4, and with a ~24-hour half-life rather than the minutes-to-hours half-life of peptide GHRPs. This distinction matters for drug interactions and for regulatory categorization.
Myth
MK-677 is a SARM.
Reality
It is not a selective androgen receptor modulator. MK-677 has no direct action at the androgen receptor and does not affect testosterone production. It is often bundled with SARMs in research-chemical retail catalogs, but the pharmacology is entirely different — MK-677 works through GH/IGF-1, not androgen signaling.
Myth
MK-677 is FDA-approved for adult GH deficiency.
Reality
It is not approved for any indication. Merck developed it through Phase II/III for multiple indications including GH deficiency, frail elderly, and Alzheimer's, but none resulted in approval. It is not a licensed drug in any major jurisdiction.
Myth
MK-677's appetite increase only affects users psychologically — it's just 'thinking about food more.'
Reality
The appetite increase is a direct pharmacological effect of ghrelin-receptor agonism — the same receptor that drives endogenous hunger signaling. Users routinely report a meaningful and sometimes difficult-to-manage increase in food-seeking behavior, not a cognitive reframing. This is why MK-677 is particularly poorly suited for cutting-phase body-composition goals despite its lean-mass preservation effects.
Myth
MK-677 is 'like oral HGH.'
Reality
It produces elevated GH and IGF-1 levels via endogenous pathways and preserves feedback regulation, which is mechanistically different from flat exogenous rhGH dosing. But the comparison oversimplifies: MK-677's sustained receptor occupancy produces a flatter GH profile than injectable GHRPs, its glycemic cost is higher than rhGH at comparable IGF-1 elevation, and the small-molecule pharmacokinetics and drug-interaction profile make it behave like a drug, not a peptide. 'Oral GH secretagogue' is accurate; 'oral HGH' is misleading.
Myth
MK-677 is undetectable in drug testing.
Reality
LC-MS/MS methods for detecting MK-677 and its metabolites in urine are well-established in anti-doping labs, including equine-sports testing. It is explicitly prohibited under WADA S2 and athletes have tested positive. Detection windows extend to several days after discontinuation.
Published Research
23 studiesLGD-4033 and MK-677 use impacts body composition, circulating biomarkers, and skeletal muscle androgenic hormone and receptor content: A case report
Characterization of growth hormone secretagogue small molecule ibutamoren (MK-0677) and its possible metabolites in thoroughbred horses for doping control
Structural basis of human ghrelin receptor signaling by ghrelin and the synthetic agonist ibutamoren
Characterization of equine liver microsome-generated metabolites of growth hormone secretagogue small molecule ibutamoren
Effect of the Orally Active Growth Hormone Secretagogue MK-677 on Somatic Growth in Rats
The Safety and Efficacy of Growth Hormone Secretagogues.
MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture: a multicenter, randomized, placebo-controlled phase IIb study.
Growth hormone secretagogue MK-677: no clinical effect on AD progression in a randomized trial.
Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial
Definitive 2-year RCT (n=65, ages 60-81) showing MK-677 increased fat-free mass by ~1.6 kg and sustained elevated GH/IGF-1 levels over 2 years in healthy older adults, though without significant improvements in functional performance or fat mass.
The effect of treatment with the oral growth hormone (GH) secretagogue MK-677 on GH isoforms
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
Effect of alendronate and MK-677 (a growth hormone secretagogue), individually and in combination, on markers of bone turnover and bone mineral density in postmenopausal osteoporotic women
Discrepancy between serum leptin values and total body fat in response to the oral growth hormone secretagogue MK-677
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.
Treatment of obese subjects with the oral growth hormone secretagogue MK-677 affects serum concentrations of several lipoproteins, but not lipoprotein(a)
Treatment with the oral growth hormone secretagogue MK-677 increases markers of bone formation and bone resorption in obese young males
Two-month treatment of obese subjects with the oral growth hormone (GH) secretagogue MK-677 increases GH secretion, fat-free mass, and energy expenditure
Pivotal body composition RCT demonstrating that 2 months of MK-677 in obese subjects increased fat-free mass by 3.0 kg, basal metabolic rate, and 24-hour GH secretion, with IGF-1 rising ~40% — establishing the compound's core metabolic effects.
MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism.
Prolonged oral treatment with MK-677, a novel growth hormone secretagogue, improves sleep quality in man
Clinical study showing MK-677 increased REM sleep duration by ~50% and stage IV sleep by ~20% in both young and older adults, providing direct evidence for the sleep-enhancing effects frequently reported by users.
Oral administration of growth hormone (GH) releasing peptide-mimetic MK-677 stimulates the GH/insulin-like growth factor-I axis in selected GH-deficient adults
Determination of a novel growth hormone secretagogue (MK-677) in human plasma at picogram levels by liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry
Stimulation of the growth hormone (GH)-insulin-like growth factor I axis by daily oral administration of a GH secretogogue (MK-677) in healthy elderly subjects
Effects of a 7-day treatment with a novel, orally active, growth hormone (GH) secretagogue, MK-677, on 24-hour GH profiles, insulin-like growth factor I, and adrenocortical function in normal young men
Early characterization study in healthy young men showing 7 days of oral MK-677 increased mean 24-hour GH concentrations by 97%, raised IGF-1 by 55%, and elevated cortisol modestly, helping define the compound's endocrine profile.
Quick Facts
- Class
- Growth Hormone Secretagogue
- Tier
- B
- Evidence
- Moderate
- Safety
- Moderate Data
- Updated
- Apr 2026
- Citations
- 23PubMed
Also known as
Tags
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Evidence Score
Clinical Trials
View Clinical TrialsLinks to ClinicalTrials.gov for reference. Listing does not imply endorsement.