Classification explainer

Is MK-677 a SARM? What ibutamoren is

By the Decadewise team Education only Last reviewed 27 July 2026 No dosing table on this page

Short answer

The classification: MK-677, also called ibutamoren, is a growth hormone secretagogue that works as an agonist at the ghrelin receptor. It is not a selective androgen receptor modulator: the papers below describe it acting at the growth hormone secretagogue receptor, and none of the sources on this page reports androgen receptor binding for it.

What that means: it prompts the pituitary to release more of the growth hormone a body already makes, which raises circulating IGF-1. A SARM works on a different receptor entirely.

The trial record: in the two randomised trials in older adults cited below, Chapman 1996 and Nass 2008, daily oral MK-677 raised growth hormone and IGF-1, added fat-free mass against placebo, and raised fasting glucose.

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

Why the label sticks: it is sold on SARM listings and keeps turning up inside products sold as SARMs, which is where the question comes from.

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.

The mechanism in one line: it does not supply growth hormone. It leans on the switch that releases it, and the first published human trial on this page 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, as both trials 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 signalling in muscle and bone.

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

The tell: the WADA list puts them in different sections, and it does so by mechanism, not by marketing.

The published human record

What the human trials measured

How to read this: each row is one published trial, with the amount that trial administered and the outcome it reported. The numbers belong to those trials and to their populations.

MK-677 in published randomised trials

Source	Population	What the trial gave	Reported result
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 litre by week 4; fasting glucose 5.4 to 6.8mmol per litre at 4 weeks
Nass, 2008	65 healthy adults aged 60 to 81	25mg by mouth once daily; 2-year trial with the primary endpoints at 1 year	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 litre; insulin sensitivity decreased

Both trials were randomised and placebo controlled. Neither had a strength or performance measure as its primary endpoint.

The result that gets left off: the 2008 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: both trials 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 sit in separate sections of the WADA Prohibited List for that reason. 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 signalling 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 it has not approved, so its safety and effectiveness are not 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 authorised 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 analysed 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 analysed 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 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.
Long-term use. FDA has stated plainly that the long-term effects of ibutamoren are unknown.
Glucose. Both trials reported fasting glucose rising, and the 2008 trial reported insulin sensitivity falling. What that means over longer periods is not reported by either of these two trials.
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.

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.

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

Last reviewed: 27 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
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.
5
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.
6
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.
7
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.
8
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 27 July 2026. wada-ama.org, 2026 Prohibited List.
9
U.S. Food and Drug Administration. Warning letter to Prime Sports Nutrition, reference 719433, 12 December 2025, and warning letter to Agebox Inc., reference 718252, 19 December 2025. Accessed 27 July 2026. fda.gov warning letter 718252.
10
United States Anti-Doping Agency. What Athletes Need to Know about Selective Androgen Receptor Modulators (SARMs). Accessed 27 July 2026. usada.org, SARMs page.

Around this page: five neighbouring 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.