MK-677 (ibutamoren): the oral growth hormone drug that is not a peptide

MK-677, also called ibutamoren, is a pill that raises growth hormone, and it is not a peptide. It is a small-molecule drug that copies the hormone ghrelin. It is on this site because it is sold next to peptides, because it works on the same receptor as ipamorelin, and because people searching for peptides keep landing on it. It is not FDA-approved for anything. In trials it raised IGF-1 and added a little lean mass without making anyone stronger, and one trial was stopped early over heart failure. Capsules or liquids sold “for research use only” are not legal for people to take.

Why a non-peptide is on a peptide site

A peptide is a short chain of amino acids. It is usually digested if swallowed, which is why most peptide drugs are injected. MK-677 is a different kind of chemical that survives the gut, and that is its whole appeal: people get a growth hormone effect without a needle.

Everything else about it looks like the peptide world. WADA lists it beside ipamorelin. FDA handles it in the same compounding categories. It is sold through the same channels, and clinics and forums discuss it in the same breath. The guide to what peptides are covers the chemistry if you want it.

The difference matters for safety in one specific way. MK-677 has been through much larger and longer human trials than most products sold as peptides, so more of its risks are actually known.

How does MK-677 work?

MK-677 switches on the ghrelin receptor, the same switch ipamorelin uses, and the pituitary responds by releasing more growth hormone. In 32 healthy adults aged 64 to 81, 25 mg a day for up to 4 weeks nearly doubled average 24-hour growth hormone, by making the natural pulses larger and without changing their number. IGF-1 (insulin-like growth factor 1, the hormone the liver makes in response) rose from 141 to 265 mcg/L at 4 weeks, into the range of young adults.

MK-677 follows the ghrelin branch of that diagram. Because ghrelin is also a hunger signal, appetite is one of its most reliable effects.

What the human trials found

Most of these trials gave 25 mg once a day by mouth, under medical supervision. That is what was studied, and it is reported here as history. No dose is established for general use, and nothing below is a guide to taking it.

The pattern repeats. The hormone numbers move reliably, and the outcome that matters to a patient mostly does not. Alzheimer’s patients had IGF-1 up by about 70% and got no benefit. Hip-fracture patients had higher IGF-1 and little functional gain.

Trials are still running, under a different name. Lumos Pharma calls ibutamoren mesylate LUM-201, and it registered a phase 3 trial in 150 children with growth hormone deficiency, begun in May 2026, with primary completion expected in December 2027. That trial screens carefully and excludes many children. A drug being tested in a monitored pediatric trial is a long way from a product someone orders online.

Does MK-677 build muscle?

It adds lean mass, and the best trial could not show it makes anyone stronger. Over a year, older adults on MK-677 gained 1.1 kg of fat-free mass and those on placebo lost 0.5 kg. Strength and function did not change, though the authors note the trial was not powered to test function.

Three details change how that number should be read.

• Weight rose by more than lean mass. The MK-677 group gained 2.7 kg in total, and limb fat rose more than on placebo. Visceral (deep belly) fat did not fall.
• Young, fit people have no comparable trial. The muscle data are in older adults and in men with obesity. For growth hormone itself, a review of fit adults found 2.1 kg more lean mass with no gain in strength or exercise capacity, and more soft tissue swelling. See peptides for muscle growth for the full picture.
• Lean mass is not all muscle. The measurement counts body water and other non-fat tissue.

How long does MK-677 take to work?

Hormone levels move in days to weeks, and any change in body composition was measured in months. IGF-1 rose by 2 weeks in the 1996 trial and was higher again at 4. Fat-free mass was up at 8 weeks in men with obesity and at 12 months in older adults. Those are measurements, and no trial has shown when, or whether, a person would feel or see a difference. The one sleep study lasted up to two weeks in 14 people and is too small to rest a claim on.

MK-677 side effects and safety signals

Side effects in the year-long trial were mostly mild, but that trial enrolled healthy older adults under close supervision. The serious signal came from frailer patients.

The heart failure signal is why FDA treats this drug differently from most on its list. FDA’s safety page puts it plainly: “Ibutamoren mesylate poses significant safety risks due to the potential for congestive heart failure in certain patients.” The published abstract does not give case counts, and we have not quoted the figures that circulate online because we could not trace them to the paper.

Growth hormone and IGF-1 are growth factors, so people with a cancer history have added reason to talk to a doctor first. We found no long-term cancer data for MK-677. Trials have excluded people with unstable medical problems, recent cancer or complicated diabetes, so they say little about those groups. Nothing here is a clean bill of health for anyone else: the heart failure case shows that a risk can stay hidden until a vulnerable group takes the drug.

Who has the most reason to avoid it

• Anyone with heart failure, or swelling and breathlessness from heart or kidney disease
• Anyone with diabetes, prediabetes or insulin resistance
• Anyone with a history of cancer
• Frail older adults, the group in which the heart failure signal appeared
• Children and teenagers, outside a supervised trial
• People who are pregnant or trying to conceive, because no safety data exist
• Tested athletes

MK-677 has no label, so this list is built from the trial results above and is not an official contraindication list.

When to get medical help

NHLBI lists these as signs of heart failure: difficulty breathing, a persistent cough, extreme tiredness, trouble sleeping lying flat, and swelling in the ankles, feet, legs or abdomen with weight gain. Call 911 for severe trouble breathing or chest pain. See a clinician soon for unusual thirst, passing urine often or hazy eyesight, which the CDC lists as diabetes symptoms. Tell any clinician what you took, since it will not show up on your medication list.

Is MK-677 FDA-approved or legal?

No, MK-677 is not FDA-approved, and there is no legal route for selling it as a supplement or for pharmacies to compound it under the bulks system.

Three points in plain English:

• It cannot be a dietary supplement. A substance first studied as a drug falls outside the supplement definition unless it was sold as a food or supplement before that. FDA says ibutamoren was not. A “growth hormone support” bottle containing it is an unapproved drug, and in the iKids case it was not even on the label.
• Category 2 is still in force. Many peptides dropped off that list in 2026 when nominators withdrew. Ibutamoren stayed.
• The October 2026 policy changes nothing here. As of November 2, 2026, HHS says it does not intend to take enforcement action over compounding of six named peptides, on conditions. MK-677 is not one of them, and it is not a peptide.

Is MK-677 banned in sport?

Yes. WADA names ibutamoren (MK-677) as a growth hormone secretagogue in section S2.2.4 of its Prohibited List, in the 2026 list and in the 2027 list that takes effect January 1, 2027. It is banned at all times. Tested athletes should also know it can appear undeclared in supplements, as the iKids case shows.

How MK-677 compares

Tesamorelin and somatropin are the only ones here that a prescriber can use for a labeled purpose. If a clinician suspects growth hormone deficiency, the route is testing and, if confirmed, approved treatment. The FDA status tracker shows how each of these stands.

Questions to ask a prescriber

MK-677 has no approved product, so there is no labeled price, insurance route or patient program. The only regulated way anyone receives it is inside a clinical trial. If you have been offered it or are already taking it:

• What am I trying to change, and is there an approved treatment for it?
• Should my fasting glucose, HbA1c and IGF-1 be checked?
• Do I have any heart, kidney or blood pressure problem that makes fluid retention risky?
• Does my cancer history or family history matter here?
• Could a product I already take contain something undeclared?
• If I want more muscle, what would resistance training and enough protein do for me?