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Some human trialsFDA 503A Category 2

MK-677 (Ibutamoren) side effects

Also known as: MK-677 · Ibutamoren · Ibutamoren mesylate · MK-0677 · MK677 · LUM-201 · L-163,191

Updated 26 sources

11 side effects reported for MK-677 (Ibutamoren): 7 from studies and labels, 4 from users and guides. 4 come with the ways people manage them.

MK-677 (Ibutamoren) overview

Side effects reported in studies and labels

Rates as each trial or label states them. A rate from one trial does not carry over to research-grade vials or other doses.

From trials and regulators7

Clinical studies and regulatory documents.

  • More appetite

    The most frequent side effect in the 2-year trial; it subsided within a few months

  • Mild leg swelling and water retention

    Transient, mild lower-leg swelling was among the most frequent effects in the 2-year trial. FDA lists water retention among its side effects

  • Muscle pain

    Transient, among the most frequent effects in the 2-year trial

  • Higher blood sugar, lower insulin sensitivity

    Fasting glucose rose about 5 mg/dL over 2 years. At 25 mg in older adults it went from 5.4 to 6.8 mmol/L in 4 weeks. Glucose tolerance worsened in obese men

    How people manage it

    • Trials tracked fasting glucose; the people at most risk are those who already have prediabetes or diabetes.

  • Weight gain

    Body weight rose 2.7 kg over the first year vs 0.8 kg on placebo, part lean mass and part limb fat

  • Heart failure in frail patients

    A trial in elderly hip-fracture patients was stopped early over a congestive heart failure signal in a limited number of patients. FDA cites it as the reason for its Category 2 listing

    How people manage it

    • Seek care for breathlessness, chest pain or rapid swelling with weight gain.

  • Cortisol and prolactin changes

    Cortisol rose 47 nmol/L over 2 years; shorter studies saw no change or only a transient rise. Prolactin rose 23% but stayed in the normal range

Side effects users and guides report

What people post and what dosing guides list. These are reports, not measured rates.

From users and guides4

Community reports, competitor and vendor guides, media.

  • Lethargy

    Guides list it as common, mostly in the first 2 to 3 weeks; app users log fatigue often

    How people manage it

    • Guides move the dose to bedtime.

  • Numbness or tingling in the hands

    Carpal-tunnel-like symptoms from water retention, per guides

    How people manage it

    • Guides treat it as an early sign to lower the dose.

  • Joint stiffness

    Less common; typically weeks 4 to 8 and often resolves, per one guide

  • Vivid dreams

    Reported by guides in the first week or two

Who should avoid it, and what not to combine

  • Heart failure or serious heart diseaseCondition

    The hip-fracture trial stopped over a heart-failure signal, and FDA lists that risk. Water retention can strain a weak heart.

  • Diabetes or prediabetesCondition

    MK-677 raises fasting glucose and lowers insulin sensitivity in trials; guides tell people with diabetes to monitor closely or avoid it.

  • Active cancerCondition

    GH and IGF-1 can feed tumour growth, so guides list active cancer as a reason to avoid.

  • Pregnancy and breastfeedingCondition

    No safety data.

  • Insulin and diabetes drugsSubstance

    Guides say doses may need adjusting because MK-677 impairs glucose tolerance.

  • Growth hormone (somatropin)Substance

    Guides say not to combine: one or the other.

How much is known

Some human trials

Randomized trials up to 2 years (65 older adults), 12 months (563 with Alzheimer's) and 24 weeks (123 hip-fracture patients), plus many short endocrine studies, almost all at 25 mg a day. GH and IGF-1 rise reliably and lean mass rises, without strength or function gains. No benefit in Alzheimer's; a heart-failure signal in frail patients. A pediatric Phase 3 trial is recruiting.

Sources for these side effects

10 sources, each checked by date. Record updated Oct 24, 2026. Numbers are restated in our own words and labelled by where they came from.

Competitor guide3

  1. MK-677PeptidesExplorer · checked Oct 24, 2026
  2. MK-677 (Ibutamoren) dosage guideBodyHackGuide · checked Oct 24, 2026
  3. MK-677 (Ibutamoren) protocol guidePathToPeptides · checked Oct 24, 2026

Community-reported1

  1. MK-677 (self-logged reports)PeptIQ, via a competitor guide · checked Oct 24, 2026

Back to the full MK-677 (Ibutamoren) page for dosing, the vial chart and storage.