No, MK-677 is not a peptide. Ibutamoren is a small synthetic molecule — chemical formula C27H36N4O5S — that activates the same receptor the hormone ghrelin uses, the growth hormone secretagogue receptor (GHS-R1a). A peptide is a short chain of amino acids. MK-677 contains no amino acid chain at all, which is exactly why it can be swallowed as a capsule rather than injected. The US National Library of Medicine classifies it under indoles and spiro compounds, not peptides.
It gets filed under “peptides” everywhere, including on clinic menus, because it does the same job as the growth hormone peptides — it raises your own growth hormone and IGF-1. Same destination, completely different vehicle. That distinction matters more than it sounds, because the two groups differ in how they are taken, how long they act, and — most importantly — in their regulatory status and safety record.
Below: what MK-677 actually is, what the human trials found (including the one that was stopped early), the doses those trials used, the side effects with real numbers attached, and where it currently stands with the FDA. We have included the unflattering findings, because a page that only lists benefits is not useful to someone deciding whether to take something daily for months.
MK-677 versus the growth hormone peptides
| MK-677 (ibutamoren) | GH peptides (sermorelin, ipamorelin, CJC-1295, tesamorelin) | |
|---|---|---|
| Chemical class | Non-peptide small molecule | Chains of amino acids |
| Receptor | Ghrelin receptor (GHS-R1a) | Mostly the GHRH receptor; ipamorelin also acts at GHS-R1a |
| Route | Oral capsule | Subcutaneous injection (digestion would destroy them) |
| Duration of effect | Once daily sustains raised GH and IGF-1 across 24 hours | Shorter; often dosed at night or multiple times daily |
| Appetite | Markedly increased — it is a ghrelin mimetic, and ghrelin is the hunger hormone | Generally not a prominent effect |
| FDA status | Never approved, anywhere, for any indication | Varies; tesamorelin is FDA-approved for one narrow indication |
If you are weighing the injectable options against each other, our comparison of sermorelin, ipamorelin and CJC-1295 covers that side, and the tesamorelin dosage guide covers the one growth hormone secretagogue in this space that does hold an FDA approval.
How MK-677 works
Ghrelin is the hormone your stomach releases when it is empty. Beyond making you hungry, it binds a receptor in the hypothalamus and pituitary that triggers a pulse of growth hormone. MK-677 was designed at Merck in the mid-1990s to imitate that signal in a molecule stable enough to survive the gut — the original paper is Patchett and colleagues, Proceedings of the National Academy of Sciences, 1995.
In plain terms: it does not give you growth hormone. It leans on the switch that makes your own pituitary release more of it, which in turn raises IGF-1 from the liver. Because it amplifies your existing rhythm rather than replacing it, GH still comes in pulses — in the Chapman 1996 study the drug increased the height of existing pulses and raised the troughs between them without changing how many pulses occurred.
The effect on blood levels is not subtle. In that study, 25 mg daily raised mean 24-hour growth hormone by 97 ± 23 percent, and serum IGF-1 climbed from 141 ± 21 µg/L at baseline to 265 ± 29 µg/L after four weeks — back into the range of a healthy young adult. Whether that translates into something you can feel is a separate question, and it is where the evidence gets more interesting.
What the human trials actually found
MK-677 has been studied properly, which is unusual in this category. Four trials matter.
| Trial | Size | Dose & length | Outcome |
|---|---|---|---|
| Chapman 1996, healthy adults 64–81 | 32 | 2, 10 or 25 mg 14 and 28 days | GH and IGF-1 restored to young-adult range. Fasting glucose rose significantly. |
| Nass 2008, healthy adults 60–81 | 65 | 25 mg 2 years | +1.1 kg fat-free mass vs −0.5 kg on placebo. No change in strength or function. |
| Sevigny 2008, Alzheimer’s disease | 563 | 25 mg 12 months | IGF-1 up 72.9%, but no effect on any cognitive or functional measure. |
| Adunsky 2011, hip fracture recovery | 123 | 25 mg stopped early | Terminated early for a congestive heart failure safety signal. |
The Nass trial is the one to sit with, because it is the longest and the cleanest. Two years, placebo-controlled, and the drug did what it says on the label: it put on 1.1 kg of fat-free mass while the placebo group lost half a kilo. Body weight rose 2.7 kg. And then the authors’ own finding, quoted exactly: “Increased fat-free mass did not result in changes in strength or function.”
That is the honest headline. Over two years of continuous use in older adults, MK-677 reliably changed what the body composition scan showed and did not change what the person could do. The accompanying editorial in the same issue of Annals of Internal Medicine was titled, bluntly, “not yet ready for prime time.” Notably, abdominal visceral fat — the fat most associated with metabolic risk — did not change either; the extra fat that was gained went to the limbs.
What doses have been studied
There is no approved dose of MK-677, because there is no approved use. What exists is the doses the trials used, which is a different and more honest thing to quote:
- 2, 10 and 25 mg once daily in the Chapman dose-ranging study in older adults
- 10 and 50 mg once daily in a separate Chapman study in growth-hormone-deficient adults
- 25 mg once daily in all three of the large trials — Nass, Sevigny and Adunsky
Twenty-five milligrams once daily is therefore the most-studied dose by a wide margin, and it is the dose behind both the body-composition results and the glucose findings below. It is also the strength we stock, as 25 mg oral capsules, and it is dispensed only after a consultation. Higher is not better here: the dose-ranging work showed IGF-1 rising with dose, and the adverse effects rise with it too. Anyone quoting you a “cycle” of a specific number of weeks on and off is not quoting a trial, because none of the studies cycled — they dosed continuously and measured what happened.
Side effects, with the numbers
Most pages on this subject list side effects as single words. The trials attached figures to several of them, and the figures are the part worth knowing.
Blood glucose and insulin sensitivity. This is the main one. In Chapman 1996, four weeks of 25 mg daily moved mean fasting glucose from 5.4 ± 0.3 to 6.8 ± 0.4 mmol/L — roughly 97 to 122 mg/dL, which crosses from normal into the impaired-fasting-glucose range, in one month, in people who started healthy. The two-year Nass trial found a smaller average rise of 0.3 mmol/L (5 mg/dL) and, separately, that insulin sensitivity decreased. The two figures differ substantially and we are quoting both rather than splitting the difference, but the direction is consistent in every study: growth hormone opposes insulin, and raising it raises blood sugar.
Appetite. Expected and often dramatic, because the drug deliberately activates the hunger receptor. Nass described “an increase in appetite that subsided in a few months.” For someone trying to lose fat, this is working against you.
Fluid retention. Nass reported “transient, mild lower-extremity edema and muscle pain” among the most frequent effects. Swelling of the hands and feet, joint stiffness and carpal-tunnel-type numbness are recognised effects of raising growth hormone generally.
Cortisol. Unchanged over the short studies; over two years Nass found a small but statistically significant rise of 1.7 µg/dL. Prolactin rose about 23 percent in Chapman 1996 but stayed inside the normal range — so the common claim that MK-677 “spikes prolactin” overstates what was measured.
Bone. Changes consistent with increased bone remodelling. Whether net bone density improves is genuinely unsettled, and it would be wrong to sell this as a bone-density treatment.
One finding went the other way: LDL cholesterol fell slightly in the Nass trial, by about 5.4 mg/dL, with no change in total or HDL cholesterol.
The trial that was stopped
In 2011, Adunsky and colleagues published a phase IIb trial of MK-677 in 123 elderly patients recovering from hip fracture. It did not finish. The published abstract states that the trial “was terminated early due to a safety signal of congestive heart failure in a limited number of patients,” and the authors concluded that the drug “has an unfavorable safety profile in this patient population.”
You will find specific percentages for that signal circulating online. They do not appear in the published abstract or in any FDA document we could verify, so we are not repeating them. What is on the record, and matters more, is what the FDA did with it: on 29 December 2022 the agency placed ibutamoren mesylate on its Category 2 list of bulk drug substances — substances with significant safety risks that should not be used in compounding — citing exactly this trial and stating that ibutamoren mesylate “poses significant safety risks due to the potential for congestive heart failure in certain patients.”
The practical consequence for a patient: a compounding pharmacy cannot legitimately prepare it. That is a useful question to put to any provider offering it to you.
Where MK-677 actually stands legally
This is the part most product pages leave out, and it is not complicated.
- It has never been approved. Merck developed it and trialled it for growth hormone deficiency, frailty, hip fracture recovery, Alzheimer’s disease and osteoporosis. None of those produced an approval. It is currently licensed to another company and in development for paediatric growth hormone deficiency under a different name.
- It cannot legally be sold as a dietary supplement. The FDA has determined that ibutamoren is excluded from the definition of a dietary supplement 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 supplement marketing. Any bottle sold to you as a supplement is mislabelled by definition.
- It is not a controlled substance, and it is not a SARM, despite constantly being sold alongside them. It does not act on the androgen receptor at all.
- It is banned in sport at all times. The World Anti-Doping Agency names ibutamoren (MK-677) explicitly in category S2, growth hormone secretagogues, which is prohibited both in and out of competition.
- The FDA has issued warning letters to multiple companies selling it. The most recent we are aware of, in December 2025, concerned undeclared ibutamoren mesylate found by FDA laboratory analysis in products marketed for children’s height growth.
None of this makes MK-677 uniquely dangerous. It does mean that what you are buying, from anyone, is an unapproved investigational drug with a documented cardiac safety signal, and that the quality of what is in the capsule depends entirely on who made it. That is a conversation to have with a clinician, alongside baseline blood work, rather than a purchase to make from a website.
Who should not take it
- Anyone with diabetes, prediabetes or insulin resistance. The one consistent finding across every trial is that MK-677 raises fasting glucose and reduces insulin sensitivity.
- Anyone with heart failure or significant cardiac disease, given the signal that ended the hip fracture trial and the FDA’s Category 2 listing.
- Anyone with an active or recent malignancy. Raising IGF-1 in the presence of a tumour is a theoretical concern rather than a trial finding, but it is the standard caution for every growth hormone secretagogue and we apply it here.
- Pregnancy and breastfeeding.
- Competitive athletes subject to drug testing — a positive test for a named S2 substance carries the strictest sanction tier.
- Anyone unwilling to monitor. If fasting glucose, HbA1c and IGF-1 are not going to be checked before and during, the honest answer is not to start.
If the underlying goal is muscle, recovery or body composition after 40, it is worth knowing that the options are not limited to this one — our guides to peptides for men over 40 and TRT versus peptides cover approaches with more supportive evidence behind them, and the full peptide therapy menu lists what we offer and what it costs.
Frequently asked questions
Is MK-677 considered a peptide?
No. MK-677 is a non-peptide small molecule that activates the ghrelin receptor. Peptides are short chains of amino acids, which is why they have to be injected — digestion would break them apart. MK-677 survives the gut and is taken orally, precisely because it is not a peptide. It is grouped with peptides commercially because it raises growth hormone the way some peptides do, not because of what it is.
Which peptide is closest to HGH?
None of them are HGH, and that is the point of the category. Human growth hormone is a 191-amino-acid protein given by injection and available only on prescription. The peptides used in this space — sermorelin, CJC-1295, ipamorelin, tesamorelin — prompt your own pituitary to release more of your own growth hormone, which produces a smaller and more physiological rise. Tesamorelin is the only one of them with an FDA approval, and that approval is narrow.
Does MK-677 reduce testosterone?
There is no good evidence that it does. MK-677 is not an androgen and does not act on the androgen receptor, so it does not suppress the testicular axis the way anabolic steroids or SARMs can. The published trials reported no significant changes in cortisol, prolactin or thyroid hormones at the doses studied. The caveat worth stating: testosterone was not a primary endpoint in those trials, so this is reassuring rather than conclusive.
Is MK-677 a SARM?
No, although it is sold alongside them constantly and that association is where much of its reputation comes from. SARMs act on the androgen receptor. MK-677 acts on the ghrelin receptor and has nothing to do with androgens. They do share one thing: neither is an approved drug, and both appear together on the FDA’s warning letters and the Department of Defense prohibited ingredient list.
Are MK-677 gains permanent?
No. The effect lasts as long as the drug does. Growth hormone and IGF-1 return toward baseline after stopping, and a meaningful share of the weight gained is water rather than tissue — the Nass trial measured a rise in body cell mass but also noted oedema among the most common side effects. Any body-composition change that depends on a daily capsule is a change you are renting.
Does MK-677 show up on a drug test?
On anti-doping tests, yes. Ibutamoren is named explicitly on the World Anti-Doping Agency prohibited list under S2 and is banned at all times, in and out of competition. It is not part of a standard workplace drug screen, which tests for a different set of substances entirely.
Important medical disclaimer
These statements have not been evaluated by the Food and Drug Administration. MK-677 (ibutamoren) is not an FDA-approved drug and is not approved for any indication in the United States or elsewhere; it is an investigational substance, and the FDA has placed ibutamoren mesylate on its Category 2 list of bulk drug substances presenting significant safety risks in compounding. Nothing in this article is medical advice, a recommendation to use MK-677, or a substitute for evaluation by a qualified clinician. MK-677 raises fasting glucose and reduces insulin sensitivity, and a clinical trial in hip fracture patients was terminated early because of a congestive heart failure safety signal. It is not appropriate for people with diabetes or prediabetes, heart failure or significant cardiac disease, active malignancy, or during pregnancy or breastfeeding, and it is prohibited in sport at all times. Do not obtain or self-administer research-grade compounds purchased online.
Sources referenced
Patchett AA, Nargund RP, et al. “Design and biological activities of L-163,191 (MK-0677): a potent, orally active growth hormone secretagogue.” Proceedings of the National Academy of Sciences, 1995;92(15):7001–7005. · 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 secretagogue (MK-677) in healthy elderly subjects.” Journal of Clinical Endocrinology & Metabolism, 1996;81(12):4249–4257. · Chapman IM, et al. Journal of Clinical Endocrinology & Metabolism, 1997;82(10):3455–3463. · 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.” Annals of Internal Medicine, 2008;149(9):601–611. · Blackman MR. “Use of growth hormone secretagogues to prevent or treat the effects of aging: not yet ready for prime time.” Annals of Internal Medicine, 2008;149(9):677–679. · Sevigny JJ, Ryan JM, van Dyck CH, et al. “Growth hormone secretagogue MK-677: no clinical effect on AD progression in a randomized trial.” Neurology, 2008;71(21):1702–1708. · 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.” Archives of Gerontology and Geriatrics, 2011;53(2):183–189. · US Food and Drug Administration, “Safety Risks Associated with Certain Bulk Drug Substances Nominated for Use in Compounding” — ibutamoren mesylate, Category 2, added 29 December 2022. · US Food and Drug Administration, warning letters citing ibutamoren, 2021–2025. · World Anti-Doping Agency, Prohibited List, section S2.2 growth hormone secretagogues. · Operation Supplement Safety, Uniformed Services University — MK-677 ingredient entry. · National Center for Biotechnology Information, PubChem compound summary for ibutamoren, CID 178024.
Medically reviewed by Biana Borchenko, FNP-BC (A4M) — Robertson Wellness & Aesthetics, Beverly Hills.
