Summary
MK-677 (ibutamoren) is not a peptide but an oral small molecule that activates the ghrelin receptor and raises growth hormone and IGF-1 for a full day after a single dose. It has more randomized trial data than any injectable GH secretagogue: two years of 25 mg daily in healthy older adults increased fat free mass by about 1.1 kg versus placebo but also raised fasting glucose and appetite, and a hip fracture trial was stopped early for a congestive heart failure signal. It has never been approved, FDA placed it in both 503A and 503B Category 2, and it is prohibited by WADA.
What is MK-677 (ibutamoren)?
MK-677 (ibutamoren) is an oral non peptide growth hormone secretagogue (small molecule ghrelin receptor agonist). It is also known as Ibutamoren, Ibutamoren mesylate, MK-0677, L-163,191, Nutrobal.
How does it work?
Ibutamoren is an orally active, long acting agonist of the growth hormone secretagogue receptor (GHS-R1a), the ghrelin receptor. It amplifies pulsatile GH release from the pituitary without changing GH pulse frequency, which raises IGF-1 into the young adult range in older people. As a ghrelin mimetic it increases hunger, and the GH rise reduces insulin sensitivity. Its half life supports once daily dosing.
| Cluster | Metabolic and growth hormone axis |
|---|---|
| Routes | Oral capsule or tablet, once daily (all trials and as sold) |
| Conditions studied | Growth hormone deficiency and GH secretagogue use; Muscle wasting and sarcopenia |
| Record | v3, draft, verified Sep 23, 2026 |
What does the evidence say about MK-677 (ibutamoren)?
Several randomized placebo controlled trials, mostly from the 1990s and 2000s. Nass 2008 (n = 65 healthy adults aged 60 to 81, 2 years): 25 mg daily increased fat free mass by about 1.1 kg and IGF-1 by roughly 50 to 60% versus placebo, without improving strength or function, while fasting glucose and insulin resistance increased. Svensson 1998 (n = 24 obese men, 8 weeks): fat free mass rose about 3 kg and energy expenditure increased, with no loss of fat. Murphy 1999: bone turnover markers rose in elderly adults. Sevigny 2008 (n = 563 Alzheimer patients, 12 months): no effect on disease progression. Adunsky 2011: a phase 2b hip fracture trial was terminated early for a potential congestive heart failure signal.
| Evidence type | Indexed studies | Participants (human) |
|---|---|---|
| Human randomized trials | 6 | 652 |
| Human observational studies | 0 | n/a |
| Animal studies | 0 | n/a |
| All indexed studies | 6 | 652 |
Human evidence
Chapman 1996 (healthy elderly, 4 weeks) showed 25 mg daily raised 24 hour GH and IGF-1 into the young adult range. Svensson 1998 (24 obese men, 8 weeks) found 25 mg daily raised GH and IGF-1, increased fat free mass by about 3 kg and basal metabolic rate, with no significant change in fat mass. Murphy 1999 found increased markers of bone formation and resorption in older adults. Nass 2008 (65 adults, 2 years) found 25 mg daily increased fat free mass by about 1.1 kg and appendicular lean mass versus placebo, increased fasting glucose by about 0.3 mmol/L, reduced insulin sensitivity, and caused more edema, appetite increase, and muscle pain, with no improvement in strength or function. Sevigny 2008 (563 patients with Alzheimer disease, 12 months) found no clinical benefit. Adunsky 2011 (hip fracture recovery) was stopped early due to a possible heart failure signal, which is the basis of FDA's Category 2 rationale.
Animal evidence
Ibutamoren was developed from earlier non peptide secretagogues in dog and rat models, where it produced sustained GH release and IGF-1 elevation with oral dosing. Animal data are pharmacological; the clinically relevant evidence is human.
Key studies
| Study | Design and population | Outcome | Grade |
|---|---|---|---|
| Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial2008 PMID 18981485 | Randomized, double blind, placebo controlled trial, 2 yearsn = 65 Healthy adults aged 60 to 81 | 25 mg daily increased fat free mass by about 1.1 kg and IGF-1 versus placebo; no strength or function benefit; fasting glucose and insulin resistance increased | Evidence: Human RCT evidence |
| Two-month treatment of obese subjects with the oral growth hormone (GH) secretagogue MK-677 increases GH secretion, fat-free mass, and energy expenditure1998 PMID 9467542 | Randomized, double blind, placebo controlled trial, 8 weeksn = 24 Obese men | Fat free mass increased about 3 kg and basal metabolic rate rose; no significant fat loss | Evidence: Human RCT evidence |
| 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 subjects1996 PMID 8954023 | Randomized, double blind, placebo controlled trial, 4 weeksHealthy elderly adults | 25 mg daily raised 24 hour GH secretion and IGF-1 into the young adult range | Evidence: Human RCT evidence |
| Oral administration of the growth hormone secretagogue MK-677 increases markers of bone turnover in healthy and functionally impaired elderly adults1999 PMID 10404019 | Randomized, double blind, placebo controlled trial, 9 weeksHealthy and functionally impaired elderly adults | Increased markers of bone formation and bone resorption | Evidence: Human RCT evidence |
| Growth hormone secretagogue MK-677: no clinical effect on AD progression in a randomized trial2008 PMID 19015485 | Randomized, double blind, placebo controlled trial, 12 monthsn = 563 Adults with mild to moderate Alzheimer disease | No effect on cognitive or functional progression despite IGF-1 increase | Evidence: Human RCT evidence |
| MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture: a multicenter, randomized, placebo-controlled phase IIb study2011 PMID 21067829 | Randomized, double blind, placebo controlled phase 2b trial, terminated earlyOlder adults recovering from hip fracture | Trial stopped early for a potential congestive heart failure safety signal; no functional benefit established | Evidence: Human RCT evidence |
Conditions studied
| Condition | Grade | Note |
|---|---|---|
| Growth hormone deficiency and GH secretagogue use | Evidence: Human RCT evidence | Not a peptide (oral small molecule ghrelin agonist); human trials in older adults; not approved. |
| Muscle wasting and sarcopenia | Evidence: Human RCT evidence | Added about 1.1 kg of fat free mass in older adults without a strength benefit and raised fasting glucose; a hip fracture trial stopped early over a heart failure safety signal; not a peptide and not approved. |
Is MK-677 (ibutamoren) legal in the United States?
FDA and compounding status
Not FDA approved for any use. FDA placed ibutamoren mesylate in 503B Category 2 on December 29, 2022 and in 503A Category 2 on September 29, 2023, citing the potential for congestive heart failure based on the terminated hip fracture trial. As of the FDA page current to April 22, 2026, it remains in both categories, so no licensed pharmacy or outsourcing facility can lawfully compound it. It was not among the substances withdrawn from Category 2 in April 2026. It is widely sold online as a research chemical or mislabeled supplement.
WADA status
WADA prohibited. Athletes subject to anti-doping testing should treat this as prohibited at all times unless the current prohibited list says otherwise.
Regulatory timeline
- WADA
WADA publishes the 2027 Prohibited List
WADA published the 2027 Prohibited List on September 21, 2026, and it takes effect January 1, 2027. The S2 peptide hormone and growth factor classes are unchanged. BPC-157 is still named under S0, and MOTS-c is still named under S4.4 as an activator of AMP-activated protein kinase. WADA added a note that many peptides without approval for human use fall under S0 or another section, and that a peptide not named on the list may still be prohibited. GLP-1 receptor agonists such as semaglutide and tirzepatide are still not on the list.
- WADA
WADA 2026 Prohibited List takes effect
The 2026 WADA Prohibited List took effect on January 1, 2026 and continues to prohibit the S2 peptide hormone and growth factor classes (GHRH analogs, growth hormone secretagogues, GH fragments, IGF-1 and analogs, MGF, thymosin beta-4 and derivatives, hCG and GnRH-class releasing factors in males), myostatin inhibitors, insulin and the AMPK activator MOTS-c under S4, desmopressin under S5, and BPC-157 under S0. GLP-1 receptor agonists such as semaglutide and tirzepatide are not on the list.
- WADA
WADA 2025 Prohibited List keeps peptide hormones and growth factors banned at all times
The 2025 WADA Prohibited List took effect on January 1, 2025. Section S2 (peptide hormones, growth factors, related substances and mimetics) covers GHRH analogs such as CJC-1295, sermorelin, and tesamorelin, growth hormone secretagogues such as ipamorelin, GHRP-2, GHRP-6, hexarelin, and ibutamoren (MK-677), growth hormone fragments such as AOD-9604, growth factors including IGF-1 and its analogs, MGF, and thymosin beta-4 (TB-500), and chorionic gonadotropin and releasing factors such as gonadorelin and kisspeptin (prohibited in males). Myostatin inhibitors such as ACE-031 fall under S4, insulin under S4 metabolic modulators, desmopressin under S5, and BPC-157 remains an S0 non-approved substance.
- FDA
FDA places a batch of nominated peptides in 503A Category 2
In September 2023 FDA updated its 503A bulk drug substances category lists to place a group of nominated peptides in Category 2, which means FDA identified significant safety risks and the substances may not be used in 503A compounding while the evaluation continues. Kisspeptin-10 and ibutamoren (MK-677) were added on September 29, 2023 and remain in Category 2 on the FDA page current as of April 22, 2026. BPC-157, CJC-1295, ipamorelin, AOD-9604, dihexa, DSIP, epitalon, KPV, MOTS-c, selank, semax, melanotan II, LL-37, thymosin alpha-1, and thymosin beta-4 fragment (TB-500) were also placed in Category 2 under the 503A interim policy; that same page now lists them as nominated but withdrawn (see the April 2026 event). Hexarelin, PNC-27, and 5-amino-1MQ have never appeared on the FDA category lists.
Full tracker for MK-677 (ibutamoren) or the category-wide tracker.
What published studies of MK-677 (ibutamoren) used
Ranges below are reported from published studies and labeling only. PeptideAgent does not recommend doses or protocols.
Randomized trials used 25 mg orally once daily (Chapman 1996, Svensson 1998, Nass 2008, Sevigny 2008), with 2 mg and 50 mg arms in early studies. These are research doses from trials that did not lead to approval, not a therapeutic recommendation.
Routes reported
| # | Route |
|---|---|
| 1 | Oral capsule or tablet, once daily (all trials and as sold) |
MK-677 side effects
Side effects
| # | Reported side effect |
|---|---|
| 1 | Increased appetite (the most common effect across trials) |
| 2 | Higher fasting glucose and reduced insulin sensitivity (about 0.3 mmol/L glucose rise over 2 years in Nass 2008) |
| 3 | Edema and fluid retention |
| 4 | Muscle and joint pain |
| 5 | Congestive heart failure signal that halted a hip fracture trial (FDA Category 2 rationale) |
| 6 | Transient rise in cortisol and prolactin |
| 7 | Lethargy, numbness, and tingling reported anecdotally |
| 8 | No strength or functional benefit shown despite lean mass gain |
Interactions
| # | Interaction |
|---|---|
| 1 | Insulin and oral diabetes medications: raises blood glucose and can worsen control |
| 2 | Diuretics and heart failure medications: fluid retention and the heart failure signal are relevant |
| 3 | GHRH analogs and injectable GH secretagogues: additive GH exposure, untested |
| 4 | No formal human drug interaction studies published |
Contraindications
| # | Contraindication |
|---|---|
| 1 | Heart failure or reduced ejection fraction (trial terminated for heart failure signal) |
| 2 | Diabetes or prediabetes without close monitoring |
| 3 | Active cancer (IGF-1 elevation is a theoretical tumor growth concern) |
| 4 | Pregnancy and breastfeeding (no data) |
| 5 | Athletes subject to WADA testing (prohibited at all times under S2) |
How do people access MK-677 (ibutamoren) legally?
Typical cost: Not available through licensed US channels. Products sold as research chemicals are not lawful for human use and are not verified for identity or purity.
Verified access options
Step 1
No lawful United States access path identified on the last verified date.
Step 2
Not available as an FDA approved product; FDA placed ibutamoren in both 503A and 503B Category 2, and it may not lawfully be sold as a dietary supplement.
Step 3
Products labeled research use only are not lawful for human use and are not verified for identity or purity.
Access paths are verified against public regulatory records and prescriber licensing. We never list unlicensed vendors.
Compare MK-677 (ibutamoren)
What's actually offered, and what that means for you
Licensed compounding pharmacies, clinics, and telehealth prescribers openly offer many unapproved peptides, and prescribers write prescriptions for them. That does not make MK-677 (ibutamoren) lawful. MK-677 (ibutamoren) is not FDA approved and not on the 503A bulks list, so a pharmacy has no lawful basis to compound it. [7] [8]
Enforcement is uneven. FDA mostly acts through warning letters to compounders and online sellers, Category 2 safety listings, and import alerts that let it detain shipments, rather than stopping every pharmacy. State pharmacy boards oversee pharmacies day to day, and their rules differ. [7] [10] [11] [12] [13]
What changes for you
- No FDA review of the product: FDA does not check a compounded drug's safety, effectiveness, or quality before it is sold. [13]
- Identity, purity, sterility, and dose accuracy can vary from batch to batch. [7]
- Insurance rarely covers it, so you usually pay cash.
- For tested athletes, MK-677 (ibutamoren) is prohibited at all times on the WADA list, whatever the source. [9]
What to check
These checks lower some risks, but they do not make an unlawfully compounded product lawful or safe. Check for:
- A 503A pharmacy licensed in your state (your state board of pharmacy publishes license lookups). [13]
- A real evaluation by a licensed prescriber, not just an online form.
- A certificate of analysis for the specific batch.
Frequently asked questions
What is MK-677?
MK-677, also called ibutamoren, is an oral small molecule, not a peptide, that activates the ghrelin receptor and makes the pituitary release growth hormone. Taken once a day in trials, it raised 24 hour growth hormone and IGF-1. It was studied for age related muscle loss, hip fracture recovery, and Alzheimer disease but never approved. FDA lists it in Category 2 for compounding because of a heart failure signal, and it is prohibited in sport. [3] [5] [6] [7] [9]
Is MK-677 legal in the United States?
It is not an approved drug and cannot lawfully be compounded or sold as a supplement. FDA placed ibutamoren in 503B Category 2 in December 2022 and 503A Category 2 in September 2023 because of a heart failure signal, and it remains there as of April 2026. Possession is not a crime, but products sold online are unapproved drugs. [7] [8]
Does MK-677 build muscle?
It adds a little lean mass, not strength. In a 2 year randomized trial of 65 healthy older adults, 25 mg daily increased fat free mass by about 1.1 kg versus placebo and raised IGF-1 substantially, but strength and physical function did not improve. An 8 week study in obese men found about 3 kg more fat free mass and higher energy expenditure with no fat loss. Some of the lean mass gain is water. [1] [2]
What are the side effects of MK-677?
Increased appetite, fluid retention and edema, muscle pain, and higher fasting glucose with reduced insulin sensitivity were seen in the 2 year trial. The most serious concern is cardiac: a randomized hip fracture trial was stopped early because of a potential congestive heart failure signal, and FDA cites that trial in its Category 2 rationale. Tingling, lethargy, and vivid dreams are reported anecdotally. [1] [6] [7]
Is MK-677 a pill or an injection?
A pill. Unlike the injectable growth hormone peptides, ibutamoren was taken by mouth once a day in its trials, and because it is long acting a single daily dose kept growth hormone and IGF-1 raised. Being oral does not make it lawful or safer: it is unapproved, in Category 2 for both compounding pathways, and raised glucose and appetite in trials. [1] [3] [7]
How much does MK-677 cost?
There is no licensed price. FDA has treated products containing ibutamoren as unapproved drugs, and purity is not verified. Products sold as research chemicals are not lawful for human use and are not verified for identity or purity. [7]
Is MK-677 banned by WADA?
Yes. Ibutamoren is named explicitly under section S2 (growth hormone secretagogues) of the WADA Prohibited List and is prohibited at all times. It is orally active and detectable in urine, and several athletes have been sanctioned for it. [9]
MK-677 vs ipamorelin: which is better?
They act on the same ghrelin receptor. MK-677 is oral and long acting, with far more trial data, including the 2 year lean mass study and the heart failure signal. Ipamorelin is an injectable peptide with only small pharmacology studies and no outcome data. MK-677 raises glucose and appetite more because it stimulates the receptor all day. Both are in FDA Category 2 and both are WADA prohibited. [1] [7]
Does MK-677 help with sleep, bone density, or aging?
Evidence is thin. Bone turnover markers rose in older adults over 9 weeks in one trial, but fracture or bone density outcomes were not shown. The 2 year trial in older adults found no functional benefit. A 12 month trial in 563 people with Alzheimer disease found no effect on progression. Sleep effects come from small older studies and anecdote, not outcome trials. [1] [4] [5]
Decisions about starting, stopping, or combining any treatment belong with a licensed clinician who knows your history.
From the blog
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hCG, GLP-1 drugs, teriparatide, and tesamorelin have human trials and a lawful route. PT-141 is off-label for men, and kisspeptin and melanotan II have no lawful path. Ranking, legality, and WADA.
- Peptides for muscle growth, ranked by human evidence
MK-677, sermorelin, tesamorelin, CJC-1295, IGF-1 LR3, and more ranked by human evidence. None is approved for muscle growth, and all ten are banned in tested sport.
Sources
Numbered citations above point to these primary sources. PubMed entries link to the indexed abstract.
- [1]Nass R et al. Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Ann Intern Med 2008PubMed 18981485, 2008
- [2]Svensson J et al. Two-month treatment of obese subjects with the oral GH secretagogue MK-677 increases GH secretion, fat-free mass, and energy expenditure. J Clin Endocrinol Metab 1998PubMed 9467542, 1998
- [3]Chapman IM et al. Stimulation of the GH-IGF-I axis by daily oral administration of a GH secretogogue (MK-677) in healthy elderly subjects. J Clin Endocrinol Metab 1996PubMed 8954023, 1996
- [4]Murphy MG et al. Oral administration of the growth hormone secretagogue MK-677 increases markers of bone turnover in healthy and functionally impaired elderly adults. J Bone Miner Res 1999PubMed 10404019, 1999
- [5]Sevigny JJ et al. Growth hormone secretagogue MK-677: no clinical effect on AD progression in a randomized trial. Neurology 2008PubMed 19015485, 2008
- [6]Adunsky A et al. MK-0677 (ibutamoren mesylate) for the treatment of patients recovering from hip fracture: a multicenter, randomized, placebo-controlled phase IIb study. Arch Gerontol Geriatr 2011PubMed 21067829, 2011
- [7]FDA: Certain bulk drug substances for use in compounding may present significant safety risks (Category 2 list, content current as of April 22, 2026)FDA, 2026
- [8]FDA: Bulk drug substances used in compounding under section 503A of the FD&C ActFDA, 2026
- [9]WADA Prohibited List, section S2 peptide hormones, growth factors, related substances and mimetics (ibutamoren named)WADA, 2026
- [10]FDA: Compounding inspections, recalls, and other actions (warning letters to compounders)FDA
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<a href="https://peptideagent.ai/peptides/mk-677">MK-677 (ibutamoren): evidence, legality, and access</a>, PeptideAgent, updated September 23, 2026.