Peptide Comparison
MacimorelinvsMK-677 (Ibutamoren)
FDA-approved diagnostic test for adult growth hormone deficiency
The oral growth hormone secretagogue that tricks your body into producing more GH — no needles required.
At a Glance
Quick
comparison
Dose Range
Macimorelin
25–60 mg
MK-677 (Ibutamoren)
10–25 mg
Frequency
Macimorelin
As needed
MK-677 (Ibutamoren)
Once daily
Administration
Macimorelin
Oral (reconstituted solution)
MK-677 (Ibutamoren)
Oral (capsule or liquid)
Cycle Length
Macimorelin
4-6 weeks
MK-677 (Ibutamoren)
8-12 weeks
Onset Speed
Macimorelin
Rapid (hours to days)
MK-677 (Ibutamoren)
Moderate (1-2 weeks)
Evidence Level
Macimorelin
Strong human trials (Phase 3 or FDA approved)
MK-677 (Ibutamoren)
Moderate human trials (Phase 1-2)
Efficacy
Benefit
ratings
Diagnostic Accuracy
Safety & Tolerability
Convenience & Patient Experience
Muscle and body composition
Recovery and athletic performance
Sleep quality and metabolic health
Technical Data
Compound
specifications
Macimorelin
Molecular Formula
C26H30N6O3
Molecular Weight
474.6 g/mol
Half-Life
4.1 hours
Bioavailability
Oral; food decreases Cmax and AUC by approximately 50-55% — must be administered fasting
CAS Number
381231-18-1
MK-677 (Ibutamoren)
Molecular Formula
C27H36N4O5S
Molecular Weight
528.7 g/mol
Half-Life
4-6 hours (IGF-1 elevation persists ~24 hours)
Bioavailability
High oral bioavailability
CAS Number
159634-47-6
Applications
Best
suited for
Macimorelin
Diagnosis of Adult Growth Hormone Deficiency
Macimorelin is FDA-approved specifically for diagnosing AGHD in adults. It replaces the insulin tolerance test (ITT) as a safer, more convenient, and equally accurate diagnostic option. Phase 3 trials showed 87% sensitivity and 96% specificity.
Patients Intolerant or Contraindicated for ITT
For patients who cannot safely undergo insulin tolerance testing due to cardiac risk, seizure history, or other contraindications, macimorelin offers an evidence-based non-invasive alternative.
Clinical Confirmation Testing
With 97% reproducibility on retesting, macimorelin can reliably confirm GH deficiency diagnoses and monitor therapeutic responses over time with excellent consistency.
MK-677 (Ibutamoren)
Older Adults (60+) Seeking Body Composition Improvements
MK-677 was designed for aging populations. It restores GH and IGF-1 to youthful levels, increases lean mass, and improves physical function in people over 60. A 2-year clinical trial showed a 1.1 kg gain in fat-free mass with only modest fat gain—ideal for maintaining strength in older age.
Athletes and Fitness Enthusiasts Wanting Recovery Support
Oral dosing makes MK-677 convenient for athletes. It enhances muscle protein synthesis, speeds recovery after intense training, and supports lean mass building without the hassle of injections.
People with Chronic Wasting or Protein Deficiency
Clinical trials show MK-677 helps treat protein-energy wasting in kidney disease and other conditions. It stimulates appetite (a feature in these populations) and preserves muscle tissue—making it useful for those losing mass despite good nutrition.
Safety Profile
Side
effects
Macimorelin
Common
- Dysgeusia (abnormal taste)
- Dizziness
- Headache
- Fatigue
- Nausea
- Increased Appetite
Serious
- Cardiovascular events
MK-677 (Ibutamoren)
Common
- Increased appetite
- Mild water retention or edema
- Elevated fasting glucose
Uncommon
- Joint or muscle pain
- Carpal tunnel syndrome or nerve compression symptoms
- Mild nausea or digestive upset
Serious
- Glucose dysregulation and diabetes risk
Research Status
Safety
& evidence
Macimorelin
Evidence Level
Strong human trials (Phase 3 or FDA approved)
FDA Status
FDA approved for this use
Safety Overview
Macimorelin is well-tolerated with an excellent safety profile in clinical trials. No serious adverse events were reported in Phase 3 studies (n=154). Most side effects are mild and transient. QT prolongation of approximately 11 msec occurs but is generally not clinically significant. However, avoid combining with other QT-prolonging drugs.
Contraindications
- xPatients with QT prolongation or QT/RR prolongation disorder
- xConcurrent use with drugs known to prolong QT interval
- xPatients with critical illness (acute medical or surgical illness)
- xKnown hypersensitivity to macimorelin or any components
- xPatients unable to fast or follow fasting requirements
MK-677 (Ibutamoren)
Evidence Level
Moderate human trials (Phase 1-2)
FDA Status
Research compound
Safety Overview
MK-677 has been studied in hundreds of humans over 2+ years and is generally well tolerated. Most side effects are mild and manageable, especially with lower starting doses. The lack of injection requirement makes it safer than injectable GH in terms of infection risk and sterility concerns. However, it is not FDA approved and should be viewed as a research compound.
Contraindications
- xUncontrolled diabetes or severe glucose dysregulation
- xActive cancer or high cancer risk requiring caution with IGF-1 elevation
- xPregnancy or breastfeeding
Decision Guide
Which is
right for you?
Choose Macimorelin if...
- Diagnosing adult growth hormone deficiency (AGHD)
- Patients who cannot tolerate or are contraindicated for insulin tolerance test
- Clinical settings requiring convenient, repeatable hormone testing
- Healthcare providers seeking FDA-approved diagnostic alternatives
Choose MK-677 (Ibutamoren) if...
- Building lean muscle mass and strength
- Improving overall body composition in aging adults
- Enhancing athletic recovery and performance
- Supporting metabolic health and fat loss