MK-677

MK-677 (ibutamoren) is an orally active, non-peptide small molecule that raises growth hormone and IGF-1 levels by mimicking the natural hunger hormone ghrelin. Unlike most compounds on this site, it is not a peptide — it is a small synthetic drug candidate that can be taken as a pill rather than injected. It was studied by Merck and other developers in numerous published human clinical trials, including a well-known two-year study in older adults, but was never approved as a medicine anywhere due to safety findings including insulin resistance and fluid retention. It is currently being redeveloped by a different company for a specific pediatric use, while remaining unapproved for general sale; it is nonetheless sold as an unregulated supplement-style product and used off-label for bodybuilding and anti-aging purposes.

Research snapshot

Peptide category	Small-molecule ghrelin receptor agonist (not a peptide) — oral growth hormone secretagogue
Primary research interest	Growth hormone/IGF-1 elevation; historically studied for age-related frailty and adult growth-hormone-deficiency-like indications; now redeveloped for pediatric growth hormone deficiency
Highest available evidence	Tier 1 — numerous published human clinical trials, including a well-known two-year study in older adults
Human research available	Yes, extensive, including Merck-sponsored trials and current Phase 2 pediatric trials (OraGrowtH210, OraGrowtH212)
Development status	Original adult-indication program discontinued after safety findings; currently in active redevelopment for a pediatric indication under the code name LUM-201
Regulatory status	Never approved by the FDA, EMA, or any comparable regulatory body for any indication; not legally marketed as an approved drug or dietary supplement

Technical identity

Primary name	MK-677 (ibutamoren)
Alternative names	Ibutamoren mesylate; LUM-201 (current pediatric redevelopment code name)
Peptide sequence	Not applicable — this is a small molecule, not a peptide
Amino-acid length	Not applicable — this is a small molecule, not a peptide
Molecular formula	Commonly cited as C27H36N4O5S (free base); not independently re-verified in this pass
Molecular weight	Commonly cited around 528.7 g/mol (free base); not independently re-verified in this pass
CAS Registry Number	Commonly cited as 159752-10-0; not independently re-verified in this pass
PubChem CID	Not independently re-verified in this pass
Peptide class	Not applicable — small-molecule ghrelin receptor agonist
Primary biological target	Ghrelin receptor (GHS-R1a), stimulating pituitary growth hormone release and downstream IGF-1 production
Developer or originator	Originally developed by Merck; currently in clinical redevelopment by Lumos Pharmaceuticals
Development status	Not approved; active Phase 2 pediatric program ongoing under Lumos Pharmaceuticals

What is MK-677?

MK-677, also known by the generic name ibutamoren, is a small, orally active molecule that acts on the same receptor as the natural hunger hormone ghrelin. It is important to be clear about what it is not: it is not a peptide, not an injectable amino-acid chain, and not related structurally to compounds like GHRP-2 or GHRP-6, even though it produces a broadly similar downstream effect (raising growth hormone). It is a conventional small-molecule drug candidate that can be taken as an oral capsule.

MK-677 was originally developed in the 1990s, with early work associated with Merck (under the code names MK-677, MK-0677, and L-163,191), as part of a broader search for orally available growth hormone secretagogues that could avoid the need for injectable growth hormone or injectable GHRP peptides. It was studied in a substantial number of published human clinical trials over the following two decades, in populations including healthy older adults, children being evaluated for growth hormone-related conditions, patients recovering from hip fracture, and even a trial exploring whether it could slow the progression of Alzheimer’s disease (it did not show a clinical benefit for that indication).

Despite this substantial clinical trial history, MK-677 was never approved as a marketed drug by its original developers, and general development for adult indications appears to have been discontinued, reportedly due to safety signals including increased insulin resistance, fluid retention, and other metabolic effects seen in the sustained-use trials. More recently, a different company, Lumos Pharmaceuticals, has been developing an oral formulation of ibutamoren under the code name LUM-201 specifically for pediatric growth hormone deficiency and related short-stature conditions, running its own separate clinical trial program (including trials named OraGrowtH210 and OraGrowtH212). This redevelopment effort is distinct from, and more recent than, the original 1990s-2000s Merck-era research program.

How does it work?

Plain-English explanation

MK-677 works by mimicking the effect of ghrelin, the hormone that naturally rises when you’re hungry and, among other things, tells the pituitary gland to release growth hormone. Because MK-677 can be taken as a pill and stays active in the body for a long time, a single daily dose can produce a sustained rise in growth hormone and, downstream, IGF-1 — without requiring an injection.

Technical explanation

MK-677 is a potent, orally bioavailable, non-peptide agonist of the growth hormone secretagogue receptor (GHSR-1a), the same ghrelin receptor targeted by peptide GHRP-family compounds. Activation of GHSR-1a at the pituitary stimulates pulsatile GH release; clinical studies have reported that single or repeated MK-677 dosing can substantially increase GH secretion (some sources describe increases on the order of roughly 97% relative to baseline pulsatile secretion) and produce sustained elevations in IGF-1 with chronic daily dosing, distinguishing it from short-acting injectable secretagogues. Because it works through the ghrelin receptor rather than mimicking growth hormone itself, it also carries ghrelin’s associated downstream effects, including appetite stimulation and effects on glucose and insulin sensitivity, which have been documented in its clinical trial safety data.

Potential benefits and research applications

Increasing growth hormone and IGF-1 in healthy older adults (published human clinical evidence)

What is being investigated: whether daily oral MK-677 can restore GH/IGF-1 levels toward a more youthful range in older adults and produce meaningful changes in body composition. How the effect might occur: sustained GHSR-1a agonism driving repeated GH pulses and elevated IGF-1. Evidence: has been shown in a randomized, placebo-controlled two-year trial in 65 healthy adults aged 60-81 (Nass et al., 2008, Annals of Internal Medicine), which found that a 25 mg daily oral dose raised GH and IGF-I to young-adult ranges and increased fat-free mass relative to placebo, without significant change in total or visceral fat mass. Strength: this is one of the stronger, longer-duration published human trials for any compound discussed on this site. Limitation: the same trial documented meaningful adverse effects (see below), and the intervention did not improve total or visceral fat mass, limiting its case as a body-composition therapy.

Sleep quality (published human clinical evidence)

What is being investigated: whether MK-677 improves sleep quality, based on growth hormone’s natural role in sleep architecture. How the effect might occur: elevated GH/IGF-1 signaling affecting slow-wave sleep. Evidence: a published study (Copinschi et al.) reported that prolonged oral treatment with MK-677 improved sleep quality measures in the men studied. Strength: this represents genuine, if limited, published human clinical evidence for a specific sleep-related outcome. Limitation: this was a small, short-term study, and sleep-quality improvement has not been established as a validated general indication.

Growth hormone deficiency in children (ongoing human clinical trials, not yet approved)

What is being investigated: whether ibutamoren, redeveloped as LUM-201 by Lumos Pharmaceuticals, is a safe and effective oral alternative to injectable growth hormone for children with growth hormone deficiency or related short-stature conditions. How the effect might occur: sustained GHSR-1a stimulation supporting the child’s own GH secretion rather than replacing GH directly. Evidence: is being investigated in an active clinical trial program (including the OraGrowtH210 and OraGrowtH212 studies), which have been reported to meet primary and secondary endpoints in earlier-phase results. Strength: this is a genuine, currently active, registered clinical development program. Limitation: this program has not yet resulted in regulatory approval, and it applies to a specific pediatric formulation and dosing strategy that is not the same as adult off-label or bodybuilding use.

Alzheimer’s disease progression (published human clinical evidence of no benefit)

What is being investigated: whether raising GH/IGF-1 via MK-677 could slow cognitive decline in Alzheimer’s disease. How the effect might occur: theorized neuroprotective or metabolic effects of elevated GH/IGF-1 signaling. Evidence: a randomized clinical trial found no clinical benefit of MK-677 on Alzheimer’s disease progression. Strength: this is a clear negative finding from a controlled human trial, useful for correcting overstated claims. Limitation: none beyond the trial’s own scope; the finding does not generalize to unrelated proposed uses.

Muscle gain and anti-aging claims in healthy adults using unsupervised dosing (community-reported, largely unestablished)

What is being investigated: whether MK-677 meaningfully builds muscle or reverses aging-related decline when used by healthy adults outside a clinical protocol. How the effect might occur: theorized via the same GH/IGF-1 elevation demonstrated in the Nass et al. trial. Evidence: has been reported anecdotally in bodybuilding and longevity communities; the closest formal evidence is the Nass et al. trial, which showed a fat-free mass increase but no significant fat-mass reduction, alongside documented adverse effects. Strength: has not been established as a body-recomposition or anti-aging therapy beyond what that one trial showed, and that trial’s adverse-effect profile is directly relevant to anyone considering unsupervised long-term use. Limitation: unsupervised community dosing is not medically monitored for the glucose and insulin effects documented in the clinical literature.

What dosage information circulates?

Figures in this section summarize amounts and schedules reported in published research or circulating online. Their inclusion documents what is reported and does not establish that a regimen is verified, safe, effective, or appropriate.

Amounts studied in human research

The best-documented published human dosing for MK-677 is 25 milligrams taken orally once daily, used in the Nass et al. (2008) two-year randomized trial in 65 healthy older adults and in the Copinschi et al. sleep-quality study. Other published trials, including pediatric studies of the redeveloped LUM-201 formulation and earlier dose-ranging pharmacology studies, have used other doses and schedules; this session did not fully catalog every dose used across MK-677’s multi-decade trial history, and the exact doses used in the pediatric LUM-201 program in particular were not independently confirmed in this research pass.

Amounts studied in animal research

Not consistently reported. MK-677 has been used in various preclinical pharmacology studies characterizing GHSR-1a agonism, but a consolidated, independently verifiable set of animal dosing figures specific to MK-677 was not identified in this research pass.

Practitioner and community-reported protocols

Bodybuilding, longevity, and peptide-community sources widely describe MK-677 doses in the range of roughly 10 to 25 milligrams taken orally once daily, most commonly at bedtime, for extended periods (often described as many months to indefinitely) — this is one of the few instances on this site where the community-repeated figure (25 mg once daily) directly overlaps with an actual published human clinical trial dose (the Nass et al. 25 mg regimen), rather than being an unsourced figure. That said, the community use of this dose is typically unsupervised and without the medical monitoring for glucose, insulin sensitivity, and fluid retention that the source clinical trial included, and lower community-reported doses (around 10 mg) do not have the same direct trial-dose correspondence and are best treated as self-titrated, unsourced practice.

Side effects, risks, and limitations

The published Nass et al. (2008) trial documented several adverse effects with sustained 25 mg daily dosing in older adults: increased appetite (which subsided after a few months in most participants), transient mild lower-extremity edema (fluid retention) and muscle pain/joint discomfort, a modest increase in fasting glucose, decreased insulin sensitivity, elevated cortisol levels, and changes consistent with increased bone remodeling. These are documented findings from a controlled human trial, not anecdotal reports, and they represent real considerations for anyone using MK-677 outside a monitored setting, since insulin resistance and edema in particular are relevant to people with pre-existing metabolic or cardiovascular conditions. Community reports add lethargy and increased hunger as commonly experienced effects consistent with the trial data. Long-term safety beyond the two-year trial window has not been established in controlled human research. Because MK-677 sold outside an approved clinical or pharmaceutical context is an unregulated product, additional general risks apply regardless of the molecule’s own pharmacology, including unverified purity, unverified concentration, and inconsistent labeling.

Regulatory and developmental status

MK-677 (ibutamoren) has never been approved by the FDA, the EMA, or any comparable regulatory body for any indication, and it is not legally marketed in the United States as an approved drug or dietary supplement. Its original adult-indication development program does not appear to have been completed or resubmitted for approval. It is currently in active clinical redevelopment by Lumos Pharmaceuticals under the code name LUM-201, specifically for pediatric growth hormone deficiency and related short-stature indications, with published Phase 2 results (OraGrowtH210 and OraGrowtH212) reported to have met their endpoints; this program has not yet resulted in approval as of the last review of this entry. Ibutamoren is also included on prohibited-substance lists for competitive sports (for example, as a banned growth hormone-related agent), separate from its regulatory status as an unapproved drug.

Frequently asked questions

What is MK-677 (ibutamoren)?

MK-677 is an orally active, non-peptide small molecule that raises growth hormone and IGF-1 by activating the ghrelin receptor. Unlike peptide GH secretagogues, it is taken as a pill rather than injected.

How does MK-677 work?

It activates the same ghrelin receptor (GHSR-1a) that peptide GHRPs target, causing the pituitary gland to release growth hormone, and it stays active in the body long enough to produce a sustained rise in GH and IGF-1 with once-daily oral dosing.

What dosage has been studied in clinical trials?

25 milligrams taken orally once daily is the best-documented published human clinical dose, used in a two-year trial in healthy older adults and in a separate sleep-quality study. Other doses have been used in other trials, including pediatric studies of the redeveloped LUM-201 formulation, which this session did not fully catalog.

What dosage commonly circulates online?

Community and vendor sources widely describe 10 to 25 milligrams once daily, usually at bedtime. The 25 mg figure specifically overlaps with an actual published clinical trial dose, though community use of it is unsupervised and unmonitored compared with that trial.

Has MK-677 been studied in humans?

Yes, extensively, including a two-year randomized controlled trial in older adults, a sleep-quality study, an Alzheimer’s disease trial that found no benefit, and an active pediatric clinical trial program under the name LUM-201.

What side effects have been reported?

A published clinical trial documented increased appetite, transient fluid retention and muscle/joint discomfort, increased fasting glucose, decreased insulin sensitivity, elevated cortisol, and increased bone remodeling markers with sustained daily use.

Is MK-677 approved for use?

No. It has never been approved as a drug for any indication. It is currently in active clinical development for a specific pediatric use under the name LUM-201, but that program has not yet led to approval.

How strong is the evidence for MK-677’s effects?

The GH/IGF-1-raising effect and its associated adverse effects are backed by real, published, controlled human trials, which is stronger evidence than exists for many other compounds discussed on this site. Claims of significant fat loss or broad anti-aging benefit in healthy adults are not supported by that same evidence and remain largely anecdotal.

What remains unknown about MK-677?

Long-term safety beyond the roughly two-year trial window has not been established, and the outcome of the ongoing pediatric LUM-201 development program, including whether it will lead to eventual approval, is not yet known.

Bottom line

MK-677 (ibutamoren) is a non-peptide, orally active growth hormone secretagogue with an unusually solid published human clinical trial history compared with most compounds discussed on this site, including a well-conducted two-year trial in older adults and an active pediatric redevelopment program. Its GH/IGF-1-raising effect is well established, but so are documented adverse effects — increased insulin resistance, fluid retention, and elevated cortisol among them — from the same controlled trial that supports its efficacy claims. It has never been approved as a drug, the community-standard 25 mg dose does happen to overlap with an actual clinical trial dose (unlike most “circulating” figures on this site), but self-administration outside a monitored clinical setting carries the same documented metabolic risks without the same oversight.