Ibutamoren (MK-677): Side Effects
Known side effects, contraindications, and interactions
📌TL;DR
- •7 known side effects documented
- •4 mild, 2 moderate, 1 severe
- •4 contraindications listed
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Side Effects Severity Chart
Appetite stimulation is a direct consequence of GHS-R1a activation, the same receptor that mediates ghrelin's hunger-promoting effects. Reported in the majority of trial participants, typically most pronounced in the first weeks of treatment.
Mild, transient lower extremity edema is a GH-mediated effect related to sodium and fluid retention. Usually resolves within the first few months of treatment. More pronounced in elderly populations.
Fasting blood glucose increased by approximately 0.3 mmol/L (5 mg/dL) in the Nass et al. trial. GH-mediated insulin resistance may worsen glucose tolerance, particularly in prediabetic or elderly populations.
Reduced insulin sensitivity is a recognized effect of elevated GH and IGF-1 levels. May be clinically significant in populations with metabolic risk factors.
Mild muscle aches reported in some trial participants, typically transient and self-resolving.
Modest cortisol elevation observed, though levels typically remained within the normal physiological range. Clinical significance uncertain.
The Adunsky et al. hip fracture trial identified a higher CHF rate in the ibutamoren group (6.5% vs 1.7% placebo), leading to early trial termination. This risk appears concentrated in elderly patients with underlying cardiac vulnerability.
⛔Contraindications
- •History of or risk factors for congestive heart failure (identified safety signal in clinical trials)
- •Diabetes mellitus or prediabetes (MK-677 increases fasting glucose and reduces insulin sensitivity)
- •Active malignancy or history of cancer (elevated IGF-1 may promote tumor growth)
- •Not approved for human use; investigational compound only
⚠️Drug Interactions
- •Insulin and oral hypoglycemic agents: MK-677 may antagonize glucose-lowering effects through GH-mediated insulin resistance
- •Corticosteroids: Additive fluid retention risk; MK-677 already causes mild edema and cortisol elevation
- •Other GH-elevating therapies (GHRH analogs, recombinant GH): Potential for additive or synergistic GH/IGF-1 elevation; safety of combinations not established
Community-Reported Side Effects
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View community protocolsSafety Overview#
The safety profile of ibutamoren (MK-677) is characterized primarily by clinical trial data from several phase 2 studies involving predominantly elderly populations. While MK-677 was generally tolerated for its intended GH-stimulating effects, significant safety concerns emerged that contributed to the termination of clinical development.
Common Side Effects#
Increased Appetite#
Appetite stimulation is the most frequently reported side effect and is a direct pharmacological consequence of GHS-R1a activation. The ghrelin receptor is a key mediator of hunger signaling in the hypothalamus. In the Nass et al. trial, increased appetite was reported by the majority of MK-677-treated participants and was most pronounced during the initial weeks of treatment.
Peripheral Edema#
Mild, transient lower extremity edema occurred in a significant proportion of participants across trials. This effect is mediated by GH-induced sodium and water retention and is consistent with the known effects of GH therapy. Edema was typically mild and self-resolving but was more pronounced in elderly subjects.
Metabolic Effects#
MK-677's most concerning non-cardiac effects relate to glucose metabolism:
- Fasting glucose elevation: Increased by approximately 0.3 mmol/L (5 mg/dL) on average in the Nass et al. trial
- HbA1c changes: Modest increases in glycated hemoglobin were observed
- Insulin sensitivity: Declined with MK-677 treatment, consistent with the known diabetogenic effects of GH excess
These metabolic effects raise particular concern for populations already at risk for type 2 diabetes.
Serious Safety Concerns#
Congestive Heart Failure#
The most significant safety signal emerged from the Adunsky et al. hip fracture recovery trial, which was terminated early because of increased CHF rates:
| Group | CHF Events | Rate |
|---|---|---|
| Ibutamoren 25 mg | 4 of 62 | 6.5% |
| Placebo | 1 of 61 | 1.7% |
The mechanism likely involves GH-mediated fluid retention in patients with subclinical cardiac dysfunction. While this signal was detected specifically in elderly hip fracture patients (a high-risk population), it raised sufficient concern to effectively end clinical development.
IGF-1 and Cancer Risk#
Sustained elevation of IGF-1 has been associated epidemiologically with increased risk of certain cancers, including breast, prostate, and colorectal cancers. While no clinical trial of MK-677 demonstrated increased cancer incidence, the trials were too small and too short to adequately assess this risk.
Drug Interactions#
Glucose-Lowering Medications#
MK-677's insulin-resistance-promoting effects may antagonize insulin, metformin, sulfonylureas, and other antidiabetic agents. Blood glucose monitoring would be essential in any diabetic patient receiving MK-677.
Fluid-Retaining Medications#
Corticosteroids and other medications associated with fluid retention may produce additive effects when combined with MK-677, increasing the risk of edema and potentially CHF.
Population-Specific Risks#
- Elderly patients: Highest risk population based on available data; CHF signal and metabolic effects are most concerning
- Patients with cardiac history: Fluid retention may exacerbate pre-existing cardiac conditions
- Diabetic or prediabetic patients: Glucose metabolism effects may worsen glycemic control
- Cancer survivors: Theoretical IGF-1-mediated cancer risk
Related Reading#
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