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MK-677 Safety in Young Adults: What the Evidence Can Show

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Published Updated Last reviewed
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At a glance

  • FDA approval / none for ibutamoren in any indication
  • Healthy young-men evidence / 9 participants; 7 days
  • Women ages 18–29 studied in a dedicated safety trial / not identified
  • Longer metabolic evidence / includes males ages 18–50 with obesity, not a discrete young-adult cohort
  • FDA-identified concerns / hyperglycemia, liver-enzyme elevations, edema, fluid overload, and other reported events
  • Long-term young-adult incidence rates / not established
  • Fertility and pregnancy safety / not established
  • Medical review / current review of this revision is pending

Safety Starts With the Denominator

The legacy page combined short studies, older-adult trials, mechanisms, and unsourced user reports into a confident young-adult safety profile. It then invented laboratory intervals and stop rules.

FDA's 2024 multidisciplinary review reached a more bounded conclusion:

“Based on available clinical data, there are serious safety concerns related to ibutamoren mesylate use including hyperglycemia, liver enzyme elevations, edema and fluid overload”

The issuer is FDA's Center for Drug Evaluation and Research review team evaluating ibutamoren mesylate for the 503A Bulks List. The excerpt identifies cross-population concerns; it does not provide young-adult incidence, prove causality for every event, or endorse a monitoring protocol.

The Safety-Denominator Map

Evidence layerDenominator and durationSafety information it contributesBoundary
Healthy young-men crossover9 men; placebo and two experimental arms; 7 days eachIntensive hormone and cortisol profiles; short exposureCannot estimate uncommon events, long-term glucose change, fertility, or outcomes in women
Calorie-restriction crossover8 adults ages 24–39; 7 active-treatment days per periodTolerability during a controlled catabolic experimentToo small and short for a general safety rate
Obesity trial24 males ages 18–50; 8 weeksOral glucose-tolerance impairment and reported laboratory or clinical eventsMixed age range and selected metabolic phenotype
Older-adult trialsLarger and longer, including healthy older adults and hip-fracture recoveryAppetite, edema, muscle pain, fasting-glucose/insulin-sensitivity changes; CHF signal in one vulnerable populationCannot assign geriatric event rates to healthy young adults
Pediatric GHD trialsSelected prepubertal childrenGrowth, endocrine, and registered adverse-event outcomesDifferent age, diagnosis, selection, and dose framework
FDA adverse-event databasesSparse spontaneous reports with incomplete details and confoundingSignals that can prompt investigationNo exposure denominator; causality cannot be assumed

No single row is “the safety profile.” The profile has to preserve population, duration, formulation, and outcome.

What the Young-Men Trial Measured

Copinschi and colleagues enrolled nine healthy young men in a randomized, double-blind crossover study. Each participant received placebo and two MK-677 arms for seven days. The investigators measured 24-hour GH and cortisol profiles and morning IGF-1 and IGFBP-3 (PMID 8768828; DOI 10.1210/jcem.81.8.8768828).

That design is strong for within-person short-term hormone comparisons. It is weak for:

  • events occurring in fewer than one in nine exposed people;
  • harms that emerge after weeks, months, or years;
  • female reproductive outcomes;
  • pregnancy exposure;
  • sustained metabolic change;
  • clinical benefit that might justify risk; and
  • real-world products with different composition.

“No event observed” in nine people for seven days is not the same as “safe.”

What the Eight-Week Trial Adds

Svensson and colleagues studied 24 males ages 18–50 with obesity for eight weeks. The trial reported increased GH and IGF-1, increased fat-free mass, no significant change in total or visceral fat, and impaired glucose homeostasis on oral glucose-tolerance testing at weeks two and eight (PMID 9467542; DOI 10.1210/jcem.83.2.4539).

FDA's review additionally summarized drug-related events in that study involving increased glucose, transient liver-enzyme elevation, gastritis, and sweating. Those findings are directly relevant evidence. They still do not supply an event rate specifically for healthy people ages 18–29 or a validated laboratory cadence.

Figure 1

When each recorded problem appeared in the 8-week ibutamoren trial in obese men aged 18 to 50

When each recorded problem appeared in the 8-week ibutamoren trial in obese men aged 18 to 50Timeline across 8 weeks of daily treatment in 24 obese men aged 18 to 50, 12 on ibutamoren. Two people stopped after 1 to 2 weeks, one of them on ibutamoren. One person on ibutamoren had transient gastritis at week 4 and transient mild sweating at week 6. One person had a glucose of 10 mmol/L at week 6 that came down 1 week later. Oral glucose tolerance tests at weeks 2 and 8 showed impaired glucose handling in the ibutamoren group. Three transient liver-enzyme rises are not placed because their timing was not reported.Treatment: ibutamoren or placebo, 12 people eachDaily for 8 weeksStopped early2 people stoppedafter 1 to 2 weeks(1 on ibutamoren)Transient gastritis (1 person on ibutamoren)Week 4Transient mild sweating (same person)Week 6Blood glucose (1 person on ibutamoren)10 mmol/L at week6, down 1 weeklater0 wk2 wk4 wk6 wk8 wkWeeks of daily treatmentWeek 2: oral glucose tolerance test showed impaired glucose handling in the ibutamoren groupWeek 8: the impairment was still present
When each recorded problem appeared in the 8-week ibutamoren trial in obese men aged 18 to 50Timeline across 8 weeks of daily treatment in 24 obese men aged 18 to 50, 12 on ibutamoren. Two people stopped after 1 to 2 weeks, one of them on ibutamoren. One person on ibutamoren had transient gastritis at week 4 and transient mild sweating at week 6. One person had a glucose of 10 mmol/L at week 6 that came down 1 week later. Oral glucose tolerance tests at weeks 2 and 8 showed impaired glucose handling in the ibutamoren group. Three transient liver-enzyme rises are not placed because their timing was not reported.Treatment: ibutamoren or placebo, 12 people eachDaily for 8 weeksStopped early2 people stoppedafter 1 to 2 weeks(1 on ibutamoren)Transient gastritis (1 person on ibutamoren)Week 4Transient mild sweating (same person)Week 6Blood glucose (1 person on ibutamoren)10 mmol/L at week6, down 1 weeklater0 wk2 wk4 wk6 wk8 wkWeeks of daily treatmentWeek 2: oral glucose tolerance test showed impairedglucose handling in the ibutamoren groupWeek 8: the impairment was still present
The events are those FDA's 2024 review lists for this trial of 24 obese men, 12 of them on ibutamoren. Five people on ibutamoren had mild events judged drug-related; the 3 with transient ALT or AST rises are not drawn because their timing was not reported, of the two who stopped after 1 to 2 weeks, FDA gives the reasons as hypothyroidism found in pre-study testing and, in the person on ibutamoren, a 3-fold ALT and AST rise, around alcohol use against the protocol, that fell after ibutamoren was stopped. Each mark is one or two people, so the chart shows when problems were noticed, not how often they occur. Its ages come closest to young adults, but they run from 18 to 50. Sources: FDA ibutamoren evaluation for the 503A bulks list (PCAC, October 2024), cover, Human Safety, Obesity (Svensson et al. 1998b) [1]; Svensson et al., J Clin Endocrinol Metab 1998, abstract [3].
Show the numbers behind this chart
When each recorded problem appeared in the 8-week ibutamoren trial in obese men aged 18 to 50
EventFrom (week)To (week)What applies
Treatment: ibutamoren or placebo, 12 people each08Daily for 8 weeks
Stopped early122 people stopped after 1 to 2 weeks (1 on ibutamoren)
Transient gastritis (1 person on ibutamoren)44Week 4
Transient mild sweating (same person)66Week 6
Blood glucose (1 person on ibutamoren)6710 mmol/L at week 6, down 1 week later
Marker2Week 2: oral glucose tolerance test showed impaired glucose handling in the ibutamoren group
Marker8Week 8: the impairment was still present

Older-Adult Findings Need Their Labels Left On

Longer ibutamoren trials often enrolled older adults. In a two-year randomized trial of adults ages 60–81, fat-free mass increased but strength and function did not; weight, appetite, edema, muscle pain, fasting glucose, and insulin sensitivity changed (PMID 18981485; PMCID PMC2757071).

Another randomized trial in older adults recovering from hip fracture ended early after a congestive-heart-failure safety signal (PMID 21067829; DOI 10.1016/j.archger.2010.10.004).

These studies make fluid and metabolic concerns harder to dismiss. They do not show that a healthy 24-year-old has the same CHF risk as an older hip-fracture patient.

Figure 2

Ibutamoren versus placebo in adults 60 and older recovering from hip fracture: the trial stopped for heart failure

Ibutamoren versus placebo in adults 60 and older recovering from hip fracture: the trial stopped for heart failureBar chart comparing ibutamoren with placebo in a hip-fracture trial in adults 60 and older. At least one adverse event: 77% versus 55%. Serious adverse events: 24% versus 13%. Stopped because of adverse events: 11.3% versus 6.6%. Congestive heart failure: 6.5% (four people) versus 1.7% (one person). The trial was terminated early for the heart failure signal.Ibutamoren (MK-0677)PlaceboAt least one adverse event77.0%55.0%Serious adverse events24.0%13.0%Stopped because of adverse events11.3%6.6%Congestive heart failure6.5%1.7%0%20%40%60%Patients with the event (%)
Ibutamoren versus placebo in adults 60 and older recovering from hip fracture: the trial stopped for heart failureBar chart comparing ibutamoren with placebo in a hip-fracture trial in adults 60 and older. At least one adverse event: 77% versus 55%. Serious adverse events: 24% versus 13%. Stopped because of adverse events: 11.3% versus 6.6%. Congestive heart failure: 6.5% (four people) versus 1.7% (one person). The trial was terminated early for the heart failure signal.Ibutamoren (MK-0677)PlaceboAt least one adverse event77.0%55.0%Serious adverse events24.0%13.0%Stopped because of adverse events11.3%6.6%Congestive heart failure6.5%1.7%0%20%40%60%Patients with the event (%)
Percentages are as summarized in FDA's 2024 review of a randomized trial in 123 adults aged 60 or older with a recent hip fracture; the trial was stopped early because of a congestive heart failure signal. These were older, recently injured patients, not healthy young adults, so the rates cannot be carried over to people in their twenties. They show why fluid and heart effects are taken seriously, not how often they occur at younger ages. Sources: FDA ibutamoren evaluation for the 503A bulks list (PCAC, October 2024), cover, Human Safety, hip fracture (Adunsky et al. 2011) [1]; Adunsky et al., Arch Gerontol Geriatr 2011, abstract [5].
Show the numbers behind this chart
Ibutamoren versus placebo in adults 60 and older recovering from hip fracture: the trial stopped for heart failure
EventIbutamoren (MK-0677) (%)Placebo (%)
At least one adverse event7755
Serious adverse events2413
Stopped because of adverse events11.36.6
Congestive heart failure6.51.7

Separate Observed, Potential, and Unknown

Evidence statusExamples
Observed in ibutamoren clinical researchIncreased GH/IGF-1; appetite or weight change in some trials; edema or muscle pain in older adults; impaired glucose homeostasis in the obesity trial; selected liver-enzyme events
Potential based on the GH/IGF-1 axis or related approved-product labelingGlucose intolerance, fluid retention, and other axis-related concerns FDA discusses as biologically relevant
Not established for young adultsLong-term event rates, cancer causation, fertility effects, pregnancy safety, psychiatric incidence, withdrawal syndrome, and a safe exposure duration

Potential does not mean proven. Unknown does not mean absent.

Product Risk Can Dominate the Molecule Question

FDA's review found gaps in characterization of nominated ibutamoren mesylate bulk substance. Separately, FDA found undeclared ibutamoren in a product marketed to children in 2025. Neither fact says every product is contaminated; both show why a study of a defined investigational formulation cannot validate an unidentified capsule.

The young-adult dosing audit explains why study arms do not become instructions. The food and supplement review maps the missing interaction evidence, and the adolescent page distinguishes prepubertal research from teen safety.

The Responsible Bottom Line

Ibutamoren has real human safety data, but the age-specific young-adult denominator is extremely small and short. Broader trials identify meaningful metabolic, fluid, laboratory, appetite, and musculoskeletal concerns while leaving long-term young-adult incidence and product comparability unresolved. No evidence-validated monitoring schedule or “safe cycle” follows from this record.

Medical review of this revision is pending. FDA, investigators, institutions, journals, sponsors, and study authors do not endorse ibutamoren, HealthRX.com, or this page.

Frequently asked questions

Is MK-677 proven safe for people ages 18 to 29?
No. The most age-specific controlled study enrolled nine healthy young men for seven days, which cannot establish long-term or uncommon-event safety.
What adverse findings have been observed in human studies?
Across different populations, studies and FDA's review report glucose-related changes, appetite or weight changes, edema or fluid retention, muscle pain, selected liver-enzyme elevations, and other events. Rates are population-specific.
Does the older-adult CHF signal apply directly to young adults?
No. It is an important safety signal from a vulnerable hip-fracture population, not a measured incidence rate in healthy young adults.
Is there a validated blood-test schedule for young adults using ibutamoren?
No FDA-approved labeling or young-adult outcomes study establishes a monitoring interval or stop threshold.

References

  1. U.S. Food and Drug Administration, Center for Drug Evaluation and Research. Evaluation of Ibutamoren Mesylate for Inclusion on the 503A Bulk Drug Substances List. July 3, 2024; PCAC meeting October 29, 2024. See PDF pages 37–50, Human Safety and conclusions. https://www.fda.gov/media/182087/download
  2. Copinschi G; Van Onderbergen A; L'Hermite-Balériaux M; Mendel CM; Caufriez A; Leproult R; Bolognese JA; De Smet M; Thorner MO; Van Cauter E. Effects of a 7-day treatment with a novel, orally active, growth hormone (GH) secretagogue, MK-677, on 24-hour GH profiles, insulin-like growth factor I, and adrenocortical function in normal young men. The Journal of clinical endocrinology and metabolism. 1996 Aug;81(8):2776-82. DOI 10.1210/jcem.81.8.8768828. PMID 8768828. https://pubmed.ncbi.nlm.nih.gov/8768828/
  3. Svensson J; Lönn L; Jansson JO; Murphy G; Wyss D; Krupa D; Cerchio K; Polvino W; Gertz B; Boseaus I; Sjöström L; Bengtsson BA. Two-month treatment of obese subjects with the oral growth hormone (GH) secretagogue MK-677 increases GH secretion, fat-free mass, and energy expenditure. The Journal of clinical endocrinology and metabolism. 1998 Feb;83(2):362-9. DOI 10.1210/jcem.83.2.4539. PMID 9467542. https://pubmed.ncbi.nlm.nih.gov/9467542/
  4. Nass R; Pezzoli SS; Oliveri MC; Patrie JT; Harrell FE Jr; Clasey JL; Heymsfield SB; Bach MA; Vance ML; Thorner MO. Effects of an oral ghrelin mimetic on body composition and clinical outcomes in healthy older adults: a randomized trial. Annals of internal medicine. 2008 Nov 4;149(9):601-11. DOI 10.7326/0003-4819-149-9-200811040-00003. PMID 18981485. PMCID PMC2757071. https://pubmed.ncbi.nlm.nih.gov/18981485/
  5. Adunsky A; Chandler J; Heyden N; Lutkiewicz J; Scott BB; Berd Y; Liu N; Papanicolaou DA. 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 Sep-Oct;53(2):183-9. DOI 10.1016/j.archger.2010.10.004. PMID 21067829. https://pubmed.ncbi.nlm.nih.gov/21067829/
  6. U.S. Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. Accessed 2026-10-18.
Nine young adults sit inside a seven-dot observation window beside a sparse safety matrix, while older and post-surgical cohorts remain visibly separated.
HealthRX evidence illustration: Nine young adults sit inside a seven-dot observation window beside a sparse safety matrix, while older and post-surgical cohorts remain visibly separated. Image: HealthRX.com custom clinical image