MK-677 Side Effects: Is Ibutamoren Safe? What Human Trials Found

The most common MK-677 side effects in human trials were increased appetite, mild swelling from water retention, muscle and joint pain, and higher blood sugar. Less common but more serious: raised liver enzymes, higher blood pressure and, in one trial of frail older adults, heart failure that stopped the study early. Is MK-677 safe? It has not been shown to be. The FDA’s 2024 review found “serious safety concerns” and lists ibutamoren among substances that may present significant safety risks.

Below is every side effect that human trials, the FDA and published case reports have recorded, with how often it happened and how strong the evidence is. For what MK-677 is and what it does, start with our MK-677 (ibutamoren) review.

MK-677 side effects at a glance

Sources for each row are in the sections below. “Trial” means a randomized human trial; see how we grade evidence.

Is MK-677 safe?

Not established. Here is what the regulators and the trials say:

• The FDA reviewed every published trial in 2024 and concluded: “there are serious safety concerns related to ibutamoren mesylate use including hyperglycemia, liver enzyme elevations, edema and fluid overload, and CHF in elderly patients recovering from hip fracture” (FDA 2024).
• The FDA lists ibutamoren mesylate in Category 2 for compounding (substances that may present significant safety risks), “due to the potential for congestive heart failure in certain patients” (FDA Category 2 list).
• The longest trials ran 12 to 24 months, all in older adults or patients (Nass 2008, Murphy 2001). There is no long-term safety data in young, healthy people who train.
• Trials screened people out first. The hip-fracture trial excluded anyone with diabetes, cancer, uncontrolled high blood pressure or heart failure (Bach 2004).

In healthy older adults the 12-month trial called MK-677 “generally well tolerated”, with no serious adverse effects linked to it (Nass 2008). So the honest answer is: most people in trials had mild, reversible side effects, a minority had problems serious enough to cut the dose or stop, and frail patients had a heart-failure signal.

Increased appetite

MK-677 copies ghrelin, the hunger hormone, so this is the most common side effect. In the 12-month trial, 29 of 43 people on MK-677 reported more appetite vs 8 of 22 on placebo; it “subsided in a few months” (Nass 2008). In children with GH deficiency it was the most frequent drug-related side effect, 2.5 to 3 times more common than on placebo (FDA 2024). No trial has compared hunger between morning and night dosing; see MK-677 morning or night.

MK-677 water retention and swelling

Yes, MK-677 causes water retention in some people. Fluid retention is a known effect of raising GH, and approved GH medicines carry a warning about it (FDA 2024).

• How common: mild, short-lived lower-leg swelling in 19 of 43 healthy older adults on 25 mg/day vs 6 of 22 on placebo (FDA 2024). In the osteoporosis trial, 17 women on MK-677 had edema or swelling and 21 had weight gain (FDA 2024). In one set of short trials, fluid retention was no more common than on placebo (4% vs 5%) (FDA 2024).
• How much: no trial measured “water weight” directly. Over 12 months, body weight rose 2.7 kg on MK-677 vs 0.8 kg on placebo, and intracellular water (a marker of body cell mass) rose about 0.8 kg (Nass 2008).
• Is it dangerous? For most trial participants it was mild and temporary. In frail older adults after hip fracture, though, there was more edema and fluid overload (16 reports vs 10 on placebo) and more heart failure (FDA 2024, Adunsky 2011).
• Does drinking more water or cutting salt prevent it? No study has tested this.

Higher blood sugar and insulin resistance

This is the side effect that showed up most consistently in the lab results. GH counteracts insulin, so MK-677 tends to push blood sugar up.

• Fasting glucose rose from 5.4 to 6.8 mmol/L after four weeks on 25 mg/day in older adults (Chapman 1996).
• Over 12 months, fasting glucose rose about 5 mg/dL and insulin sensitivity fell (Nass 2008).
• In the Alzheimer’s trial, blood glucose rose in 15.4% of patients vs 4.6% on placebo, and HbA1c in 11.1% vs 1.4% (FDA 2024).
• After hip fracture, glucose rose 8.0 mg/dL on MK-677 vs a 1.6 mg/dL fall on placebo, and HbA1c rose 0.7% vs 0.3% (FDA 2024).
• Some participants had their dose lowered from 25 to 10 mg, and some had to stop, because of high glucose (FDA 2024).

The authors of an early trial noted the glucose rise was linked to body mass index, suggesting people already at risk are more affected (FDA 2024). Every glucose, insulin and HbA1c result is on our MK-677 and blood sugar page.

MK-677 and the heart: heart failure and blood pressure

In a Phase 2b trial of 123 adults aged 60 and over recovering from hip fracture, congestive heart failure occurred in 4 of 62 on MK-677 (6.5%) vs 1 of 61 on placebo (1.7%). Systolic blood pressure rose 11.9 to 16.4 mmHg on MK-677 vs +2.3 to −2.3 mmHg on placebo, and diastolic pressure rose 4.9 to 7.5 mmHg vs 2.2 to 3.7 mmHg. The trial was stopped early and the authors called the safety profile “unfavorable” (Adunsky 2011, FDA 2024).

Other heart-related findings:

• In the 12-month trial in healthy older adults, one person had a heart attack seven days after starting MK-677; the paper gives no judgment on cause (FDA 2024).
• Four thromboses (blood clots) were reported on MK-677 and none on placebo in an earlier hip-fracture trial; they were reported as not drug-related, without details (FDA 2024).
• In rats, MK-677 and similar drugs lowered blood pressure, while isolated rat hearts showed no effect (FDA 2024).

No study has measured heart size in MK-677 users, so claims that it does or does not cause “heart growth” are not backed by data. What the trials do show is that fluid and blood pressure effects can matter, especially in older or sick people. See also SARMs and blood pressure.

Muscle pain, joint pain, numbness and carpal tunnel

• Short-lived muscle pain: 14 of 43 on MK-677 vs 2 of 22 on placebo; two people stopped after 12 months because of joint pain (FDA 2024).
• After hip fracture: muscle pain 6.5% vs 1.7% and joint pain 8.1% vs 1.7% on placebo (FDA 2024).
• Carpal tunnel syndrome: one case in a set of short trials; in the osteoporosis trial, one case on MK-677 plus alendronate and one on placebo (FDA 2024).
• Numbness: one GH-deficient man on 50 mg had numbness in part of his right hand that lasted one day (FDA 2024).

Injected GH is known for the same set of effects: edema, joint pain and carpal tunnel syndrome (Nass 2008).

Does MK-677 affect the liver?

Liver enzyme rises do happen on MK-677, usually mild and reversible:

• In a 4-week trial, 2 older adults (7%) had reversible ALT/AST rises of 1.5 to 2.5 times the upper limit (FDA 2024).
• In the osteoporosis trial, 2 women on MK-677 stopped because their liver enzymes went above 3 times the upper limit (FDA 2024).
• Three of 12 children on the higher dose had temporary 1.5- to 4-fold rises; two also had viral illness (FDA 2024).
• A 2025 case report described a healthy man in his early 30s whose liver enzymes rose after 2 months of MK-677 and returned to normal after he stopped (Cobani 2025).

The FDA counts liver enzyme elevations among its “serious safety concerns” (FDA 2024). More on liver risk across compounds: are SARMs liver toxic?

Prolactin, cortisol and gyno

Prolactin rose 23% in older adults on 25 mg/day but stayed within the normal range (Chapman 1996). In the osteoporosis trial, three women stopped because of high prolactin (FDA 2024). Cortisol rose 47 nmol/L over 12 months in one trial (Nass 2008) but did not change in shorter trials (Copinschi 1996). No trial reported gynecomastia on MK-677; our MK-677 gyno page covers why people still report it.

Does MK-677 suppress testosterone?

Not in the way SARMs and steroids do. MK-677 does not act on the androgen receptor. In the one trial that measured it, 8 weeks of 25 mg/day in obese men lowered total testosterone vs placebo, but the testosterone/SHBG ratio (an index of free testosterone), LH and FSH did not change (Svensson 1999). That pattern points to a change in binding proteins rather than a shutdown of the hormone axis, but it is one small trial.

Stacked with a SARM it is a different story: a man taking LGD-4033 10 mg with MK-677 15 mg for five weeks had total testosterone fall 62% and free testosterone 86%, with FSH below the reference range during and after (Cardaci 2022). See MK-677 as PCT and do SARMs lower testosterone?

MK-677 anxiety, mood and mental side effects

No trial has studied anxiety on MK-677 as an outcome, so nobody knows how common it is. What has been recorded:

• In the 12-month trial in healthy older adults, a combined well-being score built from four questionnaires, including a depression inventory, did not differ between MK-677 and placebo (Nass 2008).
• In the Alzheimer’s trial, drug-related side effects were more common on MK-677, mainly fatigue, swelling, dizziness, headache, sleepiness, and psychiatric effects such as agitation and confusion (FDA 2024). These were patients with dementia, so the result may not apply to others.
• One report to the FDA’s food and supplement database described decreased activity and mood changes in a man taking a product labeled MK-677; it went away when he stopped (FDA 2024).
• Ghrelin receptors sit in brain reward areas, and the FDA notes that MK-677 “may have behavioral reinforcing properties”, although no study has shown this for ibutamoren itself (FDA 2024).

Products sold online often contain substances not on the label (Van Wagoner 2017), which is one possible explanation for unexpected effects.

Headaches, tiredness and dizziness

Headache appears in several trials and in the FDA’s list of side effects “reported in multiple studies” (FDA 2024). It is usually a single report per trial and not clearly more common than on placebo, except in the Alzheimer’s trial, where headache, dizziness, sleepiness and fatigue were among the side effects seen more often on MK-677. The full detail is on our MK-677 headache page.

Does MK-677 cause cancer?

No trial has shown that MK-677 causes cancer, but none was designed or long enough to rule it out. The concern comes from IGF-1:

• MK-677 raises IGF-1 by 40% to 94% in trials (Svensson 1998, Murphy 1999).
• Approved GH medicines carry a warning about an increased risk of tumors (neoplasm), and the FDA says the same risks may apply to ibutamoren (FDA 2024).
• The FDA also notes that higher IGF-1 levels “appeared to be associated with cancer risk across ages”, and it found no animal studies testing whether ibutamoren causes cancer (FDA 2024).
• In the 12-month trial, one person on MK-677 was diagnosed with tongue cancer and one on placebo with kidney cancer; a third developed colon cancer at the end of year 2 after a year on MK-677 and a year on placebo. The paper made no judgment on cause (FDA 2024).

Trials excluded people with cancer (Bach 2004).

Long-term MK-677 side effects

The longest data come from older adults: 12 months with a 12-month extension (Nass 2008) and 12 to 18 months in women with osteoporosis (Murphy 2001). At 12 months, fasting glucose and HbA1c were higher, body weight and limb fat had risen, and cortisol was up (Nass 2008). In the small group that stayed on MK-677 for a second year, fasting glucose was no longer significantly above baseline, so whether the rise lasts is unclear. The FDA notes a “lack of safety data” on long-term use and on the risks of keeping IGF-1 high (FDA 2024). In rats, the GH response also faded with continuous daily dosing (FDA 2024).

Case reports from people using MK-677 products

Case reports can’t prove cause, and most involve several drugs at once, but they show what doctors are seeing:

• Liver: raised liver enzymes after 2 months of MK-677, resolved after stopping (Cobani 2025).
• Breast growth and low testosterone: in a 40-year-old using supplements labeled as MK-677, RAD-140 and cardarine; lab tests found undeclared testosterone, estradiol and GH in all three; resolved after stopping (Chong 2024).
• Blood sugar crisis: in a 47-year-old with prior metabolic syndrome using MK-677 with two SARMs (summarized by the FDA 2024).
• Spleen rupture: in a 54-year-old using MK-677 with RAD-140; the authors call any link speculative (Jaffry 2026).
• Stroke: one FDA adverse event report in a 68-year-old with prior heart disease taking ibutamoren with several other drugs, including testosterone; the FDA says the role of ibutamoren can’t be judged (FDA 2024).

What the trials did to limit risk

No study has tested ways to prevent MK-677 side effects. Here is what the trial investigators did:

• Screened people first. Exclusions included diabetes, cancer, uncontrolled high blood pressure and heart failure (Bach 2004).
• Measured blood regularly. Fasting glucose, HbA1c, insulin, liver enzymes, prolactin and lipids, plus blood pressure and swelling at visits (FDA 2024).
• Lowered the dose or stopped. People with high glucose were moved from 25 to 10 mg, and some were withdrawn; others stopped for liver enzymes, prolactin, blood pressure or swelling (FDA 2024).

No trial has defined a safe dose or length of use for healthy people. The bloodwork planner explains what each marker means.

Side effects from what is not on the label

Trials used pharmaceutical-grade drug. Of 44 products sold online as SARMs, 25% contained substances not listed on the label and only 41% matched the labeled amount (Van Wagoner 2017). That is why case reports often find hormones nobody meant to take. If you look at a product’s certificate of analysis, check that it is batch-specific and from an independent lab. Sarmguide’s current partner shop is SwissChems; see our SwissChems review.

Corrections to our older MK-677 articles

This page replaces five older Sarmguide articles on MK-677 safety, water retention, anxiety, cancer and suppression. Those articles said MK-677 was “100% safe”, that it would soon be FDA-approved, that drinking more water prevents water retention, that about 10% of anxiety-prone users get anxiety, and that the cancer risk is “infinitely close to zero”. We found no evidence for any of these claims and have removed them. See our editorial policy for how we correct pages.