Classification explainer

Is MK-677 a SARM? What ibutamoren is

By the Decadewise team Education only Last updated 30 July 2026 No dosing table on this page

Short answer

The classification: MK-677, also called ibutamoren, is a growth hormone secretagogue, an agonist at the ghrelin receptor. It is not a selective androgen receptor modulator, and none of the papers below reports androgen receptor binding.

What that means: it pushes the pituitary to release more of the growth hormone a body already makes, raising IGF-1. A SARM acts on a different receptor.

The trial record: randomized trials have run in healthy adults, growth hormone deficiency, obesity, hip fracture, osteoporosis, Alzheimer disease and dialysis. All twelve raised IGF-1. One added fat-free mass against placebo at a year (Nass, 2008). The disease trials mostly reported no functional benefit.

The safety finding: a 2011 hip-fracture trial was stopped early after a congestive heart failure signal, and its authors reported an unfavorable safety profile in that population (Adunsky, 2011).

Where regulators file it: the 2026 WADA Prohibited List names ibutamoren in the growth hormone releasing factors entry at S2.2.4, not in the anabolic agents section that holds SARMs.

On this page

Short answer What is ibutamoren? What a SARM is The trial record Is MK-677 a SARM? Is it legal to sell? Is it banned in sport? Why is it sold as one? What is unsettled The safety picture How this is sourced Related pages The disclaimer

What is ibutamoren, exactly?

The origin: the molecule was built at Merck and described in 1995 as L-163,191, a nonpeptide compound that released growth hormone from rat pituitary cells with an EC50 of 1.3nM. The oral activity reported in that paper was shown in dogs, where the compound raised growth hormone at oral doses as low as 0.125 mg/kg (Patchett, 1995).

The target: a year later the same group cloned the receptor these compounds hit, a G protein-coupled receptor in the pituitary and hypothalamus that functions in growth hormone release (Howard, 1996). The class name was already in use rather than coined there: Patchett's 1995 title calls the compound a growth hormone secretagogue, and Howard's abstract refers to molecules already "termed" that.

The natural ligand: in 1999 that receptor was matched to ghrelin, a stomach peptide that releases growth hormone (Kojima, 1999). So ibutamoren is a synthetic stand-in for a gut hormone, and the 2008 trial below is titled around exactly that phrase, an oral ghrelin mimetic.

What the molecule actually does: it does not supply growth hormone. It leans on the switch that releases it, and the earliest of the healthy older adult trials reported an increase in growth hormone pulse height and interpulse nadir without a significant change in the number of pulses (Chapman, 1996).

What a SARM is, and why this is a different drug

The SARM definition: a selective androgen receptor modulator is a nonsteroidal compound that binds the androgen receptor and aims for anabolic effect in muscle and bone while sparing other androgen-responsive tissue (Dalton, 2011).

The split: the two classes are described as acting at different receptors. One is a ghrelin receptor agonist upstream of growth hormone. The other is an androgen receptor ligand. No cross-binding study between them appears in the sources here.

Ibutamoren (MK-677)

Receptor: the growth hormone secretagogue receptor, the same one ghrelin binds.

Downstream: pituitary release of growth hormone, then a rise in circulating IGF-1, which all twelve trials in the table below report.

Anti-doping class: S2, peptide hormones, growth factors, related substances, and mimetics.

The SARM class

Receptor: the androgen receptor, which the 2011 trial paper describes SARMs as binding.

Downstream: androgen receptor signaling in muscle and bone.

Anti-doping class: S1.2, other anabolic agents.

The tell: the WADA list files the two under different sections with different headings and different named examples. It prints no rationale for where that boundary sits, so we report the filing and leave the reasoning to the document that never gives it.

The published human record

What the human trials measured

How to read this: each row is one randomized trial, with the amount it administered and the outcome it reported. Murphy 1999 is a single publication pooling three separate randomized studies, and the Svensson row has four further publications reporting other endpoints from the same 24-man group. The numbers belong to those trials and to their populations.

MK-677 in published randomized trials

Source	Population	What the trial gave	Reported result
Copinschi, 1996	9 healthy young men	placebo, 5mg or 25mg by mouth at bedtime for 7 consecutive days, in a three-period cross-over	the amount of growth hormone secreted was similar in all three conditions, but pulse frequency rose at both amounts; IGF-1 up in a dose-dependent manner, IGF binding protein-3 up only at 25mg; 24-hour cortisol measures unchanged
Chapman, 1996	32 healthy adults aged 64 to 81	2, 10 or 25mg by mouth once daily, 14 and 28 day periods	at 25mg, mean 24-hour growth hormone up 97 percent at 2 weeks; IGF-1 141 to 265 micrograms per liter by week 4; fasting glucose 5.4 to 6.8mmol per liter at 4 weeks
Chapman, 1997	9 men aged 17 to 34 with severe growth hormone deficiency, all treated with growth hormone in childhood	10mg or 50mg by mouth once daily for 4 days, over two periods separated by at least 28 days	after 10mg, IGF-1 up 52 percent and 24-hour mean growth hormone up 79 percent against baseline; after 50mg, 79 percent and 82 percent; fasting and postprandial insulin and postprandial glucose rose significantly
Murphy, 1998	8 healthy volunteers aged 24 to 39, held at 18 kcal per kg per day for two 14-day periods	25mg by mouth once daily during the last 7 days of each diet period, two-period cross-over	mean daily nitrogen balance 0.31g per day against -1.48g per day on placebo; IGF-1 264 against 188 nanograms per mL over the last 5 days of treatment; IGF binding protein-3 also higher
Svensson, 1998	24 obese men aged 18 to 50 with a body mass index above 30	25mg by mouth daily for 8 weeks, parallel groups of 12	IGF-1 up about 40 percent; fat-free mass up; total and visceral fat not significantly changed; basal metabolic rate up at 2 weeks but not at 8; oral glucose tolerance testing showed impaired glucose homeostasis at 2 and 8 weeks
Murphy, 1999	187 adults aged 65 or older, pooled from three placebo-controlled studies lasting 2 to 9 weeks	5, 10, 25 or 50mg by mouth daily	IGF-1 up 55 to 94 percent; in the 105 functionally impaired subjects at 9 weeks, osteocalcin up 29.4 percent, bone-specific alkaline phosphatase up 10.4 percent and urinary N-telopeptide up 22.6 percent
Murphy, 2001	292 women aged 64 to 85 with low femoral neck bone density	25mg by mouth daily, alone or with alendronate 10mg, 12 months of treatment and 18 months of density measurement	IGF-1 up 39 to 45 percent; femoral neck density up 4.2 percent on the combination against 2.5 percent on alendronate alone; no added gain at the lumbar spine, total hip or total body
Bach, 2004	161 hip-fracture patients aged 65 or older, recruited after surgery	daily by mouth for 6 months, then 6 months of follow-up; the paper's abstract does not print the amount	IGF-1 up 84 percent against 17 percent on placebo; no significant difference against placebo on the functional performance measures or on the overall Sickness Impact Profile score
Nass, 2008	65 healthy adults aged 60 to 81	25mg by mouth once daily; 2-year trial with the primary endpoints at 1 year	growth hormone and IGF-1 rose to the levels of healthy young adults; at the 1-year primary analysis: fat-free mass +1.1kg against -0.5kg on placebo; body weight +2.7kg against +0.8kg; fasting glucose +0.3mmol per liter; insulin sensitivity decreased
Sevigny, 2008	563 patients with mild to moderate Alzheimer disease	25mg by mouth daily for 12 months	IGF-1 up 60.1 percent at 6 weeks and 72.9 percent at 12 months; no significant difference against placebo on any of the four efficacy measures
Adunsky, 2011	123 hip-fracture patients, 62 on MK-677 and 61 on placebo	25mg by mouth daily, in a 24-week study	IGF-1 up 51.4 ng per mL against placebo; gait speed better by a 0.7 score difference; stair climbing power not significant; the trial was terminated early after a congestive heart failure safety signal
Campbell, 2018	26 hemodialysis patients enrolled, 22 completed	25mg by mouth daily, one month on the drug and one month on placebo with a one-month washout between them	IGF-1 rose 65 percent more than on placebo, 95 percent confidence interval 33 to 104 percent; the authors report no serious adverse effects attributable to the drug

Every report listed carries the randomized controlled trial publication type on its PubMed record and had a placebo comparison. The primary endpoint differs from row to row, so the rows are not measuring the same thing.

The trial that stopped: the 2011 hip-fracture study was terminated early after a congestive heart failure safety signal in a limited number of patients, and its authors concluded that MK-677 has an unfavorable safety profile in that patient population (Adunsky, 2011). It is the only report on this page that ended that way.

What the larger trials found: the two hip-fracture studies and the Alzheimer study randomized 847 patients between them, and every one of them raised IGF-1. Bach reported no significant difference against placebo on its functional measures, Adunsky reported a gait-speed difference but not an improvement in most of the others, and Sevigny reported no difference on any of its four efficacy measures. Target engagement is not the same as an outcome.

The result that gets left off: the Nass trial found the added fat-free mass did not translate into a measured change in strength or function, and the authors flagged that the study was not powered to settle functional endpoints.

The other direction: Chapman and Nass both reported fasting glucose moving up, Chapman at 4 weeks and Nass at the 1-year analysis. That is a reported finding in those populations, not a prediction about anyone reading this.

Is MK-677 a SARM?

No. A SARM binds the androgen receptor; ibutamoren binds the growth hormone secretagogue receptor, which is the receptor for ghrelin. The two classes also sit in separate sections of the WADA Prohibited List. The United States Anti-Doping Agency draws the same line on its own SARMs page, which puts SARMs in the category of other anabolic agents under section S1.2 and then lists ibutamoren separately, among prohibited substances it says are sometimes marketed as SARMs.

Why the mix-up matters: the classes carry different physiology, so a claim carried across from one to the other has no basis. Growth hormone and androgen signaling are not interchangeable.

Is MK-677 legal to sell in the United States?

Not as a supplement and not as a drug. FDA has stated that ibutamoren is an active ingredient not approved by FDA, so its safety and efficacy have not been established, and that ibutamoren is excluded from the dietary supplement definition under section 201(ff)(3)(B)(ii) of the Federal Food, Drug, and Cosmetic Act because it was authorized for investigation as a new drug before any food or supplement marketing.

The enforcement record: a warning letter dated 12 December 2025 named MK-677 among products marketed as SARMs and called them unapproved new drugs. A second letter dated 19 December 2025 went to a firm whose children's growth products were found on laboratory analysis to contain undeclared ibutamoren mesylate.

What that second letter tells you: the compound turns up in products that never named it. Regulators found it by testing, not by reading a label.

Is MK-677 banned in sport?

Yes, at all times, in and out of competition. The 2026 WADA Prohibited List names ibutamoren (MK-677) at S2.2.4, in the growth hormone releasing factors entry, alongside anamorelin, capromorelin, ipamorelin, lenomorelin, macimorelin and tabimorelin. Every substance in the S2 class is a non-specified substance under the list, and the list took effect on 1 January 2026.

The section it is not in: S1.2, other anabolic agents, is where the named SARMs sit. Two different sections, two different mechanisms.

Why is MK-677 sold next to SARMs?

Because the retail category and the pharmacological one do not line up. When a testing group bought 44 products sold online as SARMs and analyzed them, only 23 contained any SARM, and another 17 contained a different unapproved drug, with ibutamoren named among them alongside GW501516 and SR9009 (Van Wagoner, 2017).

The label problem inside that same set: the stated amount matched the analyzed amount in only 18 of 44 products, and 11 contained substances that were not on the label at all.

The reading: a product sold under a class name is not evidence that it holds that class of molecule. It is evidence of what the seller typed.

What the record does not settle

The gaps we can name on this compound:

Function. The Nass two-year trial reported more fat-free mass and no measured gain in strength or function, and its authors said the study lacked power to answer that question. The three clinical trials that did take function or cognition as an endpoint did not report the improvement they were looking for.
Cardiac risk. The 2011 hip-fracture trial stopped early on a congestive heart failure signal in a limited number of patients, and FDA names an increased potential for congestive heart failure among reported effects. No trial in the table was designed to measure cardiac outcomes, so the size of that risk is not settled by this record.
Long-term use. FDA has stated plainly that the long-term effects of ibutamoren are unknown.
Glucose. Chapman and Nass both reported fasting glucose rising, and Nass reported insulin sensitivity falling. What that means over longer periods is not reported by either.
Contents. The 2017 analysis measured what 44 internet-sold products actually contained against what their labels claimed, and found the two agreed on amount in 18 of 44.

No approved product containing ibutamoren exists in the United States.

The safety picture, from the record

What the trials and the agency report: in healthy older adults the most frequent reported side effects were increased appetite, transient mild lower-limb swelling and muscle pain, with fasting glucose rising and insulin sensitivity falling over two years. The sharpest signal in the record comes from a different population: the 2011 hip-fracture trial was terminated early after a congestive heart failure safety signal, and its authors concluded that the compound has an unfavorable safety profile in those patients. FDA's own description names water retention, fatigue, altered glucose metabolism and, in some people, an increased potential for congestive heart failure, and says long-term effects are unknown. Whether any of that applies to one person is a question for a doctor with their labs in hand, not for this page.

How this page is sourced

Primary documents, with one exception: the pharmacology comes from the papers cited below, the anti-doping classification from the official 2026 Prohibited List text, and the regulatory position from FDA warning letters, each read directly. The exception is the USADA page, a secondary source carrying exactly one statement on this page, the one attributed to it by name.

How the trial list was assembled: we searched for the string (MK-677 OR MK-0677 OR ibutamoren) AND randomized controlled trial[pt] in PubMed on 30 July 2026, esearch HTTP 200, and it returned 19 records, every abstract of which we read. Three of the 19 are not a randomized trial of this compound in adults: one enrolled growth hormone deficient children, one is a review article that carries the randomized-trial index tag anyway, and one tested hexarelin rather than MK-677. Four more report additional endpoints from the same 24-man group as the Svensson row. That leaves the twelve trials in the table above, which is all of them the query reached. It is not a claim about work the query does not reach, and it is not a systematic review.

What we got wrong until 30 July 2026, stated plainly: this paragraph used to say the table carried the trials in older or clinical adult populations, and the table held seven rows. The same query returned adult trials in growth hormone deficiency, obesity, caloric restriction, healthy young men and hemodialysis that the table did not carry, so the completeness claim was false as written. Five trials were added and the accounting above replaces the claim. Every citation on the page was genuine before the correction, which is exactly why nothing looked wrong.

Twenty sources: seventeen papers with DOIs and PubMed IDs, one international standard, one entry holding two dated FDA warning letters, and one anti-doping agency page.

The standard: the full sourcing and citation-verification standard for this site, including who checks a page before it ships, lives on the methodology page.

Last reviewed: 29 July 2026.

1
Patchett AA, Nargund RP, Tata JR, et al. Design and biological activities of L-163,191 (MK-0677): a potent, orally active growth hormone secretagogue. Proc Natl Acad Sci U S A. 1995;92(15):7001-7005. doi:10.1073/pnas.92.15.7001. PMID 7624358.
2
Howard AD, Feighner SD, Cully DF, et al. A receptor in pituitary and hypothalamus that functions in growth hormone release. Science. 1996;273(5277):974-977. doi:10.1126/science.273.5277.974. PMID 8688086.
3
Kojima M, Hosoda H, Date Y, Nakazato M, Matsuo H, Kangawa K. Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature. 1999;402(6762):656-660. doi:10.1038/45230. PMID 10604470.
4
Copinschi G, Van Onderbergen A, L'Hermite-Balériaux M, et al. 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. J Clin Endocrinol Metab. 1996;81(8):2776-2782. doi:10.1210/jcem.81.8.8768828. PMID 8768828. Record and pagination confirmed through CrossRef on 30 July 2026, HTTP 200.
5
Chapman IM, Bach MA, Van Cauter E, et al. 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. J Clin Endocrinol Metab. 1996;81(12):4249-4257. doi:10.1210/jcem.81.12.8954023. PMID 8954023.
6
Chapman IM, Pescovitz OH, Murphy G, et al. 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. J Clin Endocrinol Metab. 1997;82(10):3455-3463. doi:10.1210/jcem.82.10.4297. PMID 9329386. Record and pagination confirmed through CrossRef on 30 July 2026, HTTP 200.
7
Murphy MG, Plunkett LM, Gertz BJ, et al. MK-677, an orally active growth hormone secretagogue, reverses diet-induced catabolism. J Clin Endocrinol Metab. 1998;83(2):320-325. doi:10.1210/jcem.83.2.4551. PMID 9467534. Record and pagination confirmed through CrossRef on 30 July 2026, HTTP 200.
8
Svensson J, Lönn L, Jansson JO, et al. Two-month treatment of obese subjects with the oral growth hormone (GH) secretagogue MK-677 increases GH secretion, fat-free mass, and energy expenditure. J Clin Endocrinol Metab. 1998;83(2):362-369. doi:10.1210/jcem.83.2.4539. PMID 9467542. Record and pagination confirmed through CrossRef on 30 July 2026, HTTP 200. Four further publications report other endpoints from this same group of 24 men and are the four the accounting above sets aside as duplicates: PMID 9661080, PMID 10468903, PMID 10372705 and PMID 12550076.
9
Murphy MG, Bach MA, Plotkin D, 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. 1999;14(7):1182-1188. doi:10.1359/jbmr.1999.14.7.1182. PMID 10404019.
10
Murphy MG, Weiss S, McClung M, et al. 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. J Clin Endocrinol Metab. 2001;86(3):1116-1125. doi:10.1210/jcem.86.3.7294. PMID 11238495.
11
Bach MA, Rockwood K, Zetterberg C, et al. The effects of MK-0677, an oral growth hormone secretagogue, in patients with hip fracture. J Am Geriatr Soc. 2004;52(4):516-523. doi:10.1111/j.1532-5415.2004.52156.x. PMID 15066065.
12
Nass R, Pezzoli SS, Oliveri MC, et al. Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Ann Intern Med. 2008;149(9):601-611. doi:10.7326/0003-4819-149-9-200811040-00003. PMID 18981485.
13
Sevigny JJ, Ryan JM, van Dyck CH, Peng Y, Lines CR, Nessly ML. Growth hormone secretagogue MK-677: no clinical effect on AD progression in a randomized trial. Neurology. 2008;71(21):1702-1708. doi:10.1212/01.wnl.0000335163.88054.e7. PMID 19015485.
14
Adunsky A, Chandler J, Heyden N, 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. 2011;53(2):183-189. The paper reports that the trial was terminated early because of a congestive heart failure safety signal. doi:10.1016/j.archger.2010.10.004. PMID 21067829.
15
Campbell GA, Patrie JT, Gaylinn BD, Thorner MO, Bolton WK. Oral ghrelin receptor agonist MK-0677 increases serum insulin-like growth factor 1 in hemodialysis patients: a randomized blinded study. Nephrol Dial Transplant. 2018;33(3):523-530. The 25mg daily amount and the one-month crossover periods are not in the abstract; both are stated in the paper's Materials and Methods, read in full on 30 July 2026, HTTP 200. doi:10.1093/ndt/gfw474. PMID 28340044. Record and pagination confirmed through CrossRef the same day, HTTP 200.
16
Dalton JT, Barnette KG, Bohl CE, et al. The selective androgen receptor modulator GTx-024 (enobosarm) improves lean body mass and physical function in healthy elderly men and postmenopausal women: results of a double-blind, placebo-controlled phase II trial. J Cachexia Sarcopenia Muscle. 2011;2(3):153-161. doi:10.1007/s13539-011-0034-6. PMID 22031847.
17
Van Wagoner RM, Eichner A, Bhasin S, Deuster PA, Eichner D. Chemical composition and labeling of substances marketed as selective androgen receptor modulators and sold via the internet. JAMA. 2017;318(20):2004-2010. doi:10.1001/jama.2017.17069. PMID 29183075.
18
World Anti-Doping Agency. World Anti-Doping Code International Standard: Prohibited List 2026, sections S1.2 and S2.2.4. Effective 1 January 2026. Accessed 29 July 2026. Re-checked 31 July 2026: an automated request for the list PDF returned HTTP 202 with an empty body, which is a bot challenge rather than a missing document, so this source could not be re-retrieved by script on that date. wada-ama.org, 2026 Prohibited List.
19
U.S. Food and Drug Administration. Warning letter to Prime Sports Nutrition, reference 719433, 12 December 2025, naming LGD-4033, RAD-140, MK-677 (Ibutamoren) and S-23 as products marketed as SARMs and treating them as unapproved new drugs under section 505(a). Warning letter to Agebox Inc., reference 718252, 19 December 2025, on undeclared ibutamoren mesylate confirmed by laboratory analysis, the section 201(ff)(3)(B)(ii) exclusion, and the reported side-effect and long-term-effect statements. Both accessed 29 July 2026.
20
United States Anti-Doping Agency. What Athletes Need to Know about Selective Androgen Receptor Modulators (SARMs). Accessed 27 July 2026. Re-retrieved 31 July 2026, HTTP 200, 892,800 bytes: the page reads "SARMs are listed in the category of "Other Anabolic Agents" under section S1.2 of the WADA Prohibited List." The lane that could not reach it on 31 July was requesting a different USADA path; the URL cited here resolves. usada.org, SARMs page.

Around this page: five neighboring pages that cover the classification questions next to this one.

Is ostarine a steroid: the same classification question aimed at the androgen receptor side, with the statutory definition of an anabolic steroid.
Cardarine (GW501516) explained: another compound the 2017 analysis detected in products sold as SARMs, with its own sources.
Ipamorelin guide: another growth hormone secretagogue named in the same WADA entry.
Tesamorelin guide: a releasing-hormone analogue, filed one bullet above the secretagogues on the same list.
How to read a COA: what a certificate of analysis tests, read beside what the 2017 product analysis found.

The briefing: classification reads like this one ship in The Decadewise briefing before they land anywhere else.

The disclaimer

Every page is reviewed by medical professionals before it ships, and written with longtime biohackers who were doing this before it was a trend. Reviewed still does not mean prescribed: nothing here is medical advice. It is research, trial data, and reported use, with the numbers intact so you can check them. For decisions about your body, see a doctor who can look at your labs.