At a Glance
Quickcomparison
Dose Range
Tabimorelin
100–500 mg
MK-677 (Ibutamoren)
10–25 mg
Frequency
Once daily
Administration
Oral (capsule or solution)
Oral (capsule or liquid)
Cycle Length
4-6 weeks
8-12 weeks
Onset Speed
Moderate (1-2 weeks)
Evidence Level
Moderate human trials (Phase 1-2)
Efficacy
Benefitratings
Growth Hormone Stimulation
Convenience & Compliance
Selectivity & Safety Profile
Muscle and body composition
Recovery and athletic performance
Sleep quality and metabolic health
Technical Data
Compoundspecifications
Molecular Formula
C32H40N4O3
Molecular Weight
528.7 g/mol
Half-Life
Several hours (exact human half-life not published; dose-dependent pharmacokinetics)
Bioavailability
Orally active with dose-dependent bioavailability (increases at higher doses)
CAS Number
193079-69-5
C27H36N4O5S
4-6 hours (IGF-1 elevation persists ~24 hours)
High oral bioavailability
159634-47-6
Protocols
Dosingtiers
standard
1.5 mg/kg per day (3 mg/kg first and last dose)
7-day study course
Dose used in GH-deficient adults (1 week course, 3 mg/kg first and last dose) [2]; significant GH release seen at 3 mg/kg and above in single-dose healthy-volunteer studies [1].
starting
10 mg
2-4 weeks initial
Lower entry dose used in practice to limit water retention and appetite surge before titrating up.
25 mg
Studied up to 1-2 years
25 mg once-daily oral is the dose used in the randomized trial in healthy older adults; increased GH/IGF-1 and fat-free mass [1]. Most-studied dose [2].
Applications
Bestsuited for
+Stimulates growth hormone release from the pituitary gland through ghrelin receptor activation
+Orally active—no injections required, making it convenient for daily use
+Dose-dependent growth hormone and IGF-1 elevation at therapeutic doses
+Does not significantly raise ACTH, cortisol, or prolactin at most doses, showing better selectivity than some competing GH-releasing peptides
+Well-tolerated in short-term human studies with generally mild adverse effects
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
Sideeffects
Common
Headache
Nausea
Appetite stimulation
Dizziness
Dry mouth
Serious
Drug-drug interactions via CYP3A4 inhibition
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
Glucose dysregulation and diabetes risk
Research Status
Safety& evidence
FDA Status
Research compound
Safety Overview
Tabimorelin is an oral GHS-R agonist with preclinical and early clinical data indicating dose-dependent appetite stimulation (potentially problematic for weight-conscious users) and transient blood glucose elevation due to GH's insulin-antagonistic effects. No human safety database exists beyond Phase 1/2 studies—efficacy and long-term safety profile in humans remain incompletely characterized. Potential risks include carpal tunnel syndrome (documented with chronic GH therapy), arthralgias, and theoretical tumor growth acceleration, though these are extrapolated from GH physiology rather than directly observed in limited human exposure.
Contraindications
xActive or history of carcinomas (ghrelin receptor agonists may stimulate growth of certain tumors)
xConcurrent use of potent CYP3A4 substrates due to risk of dangerous drug-drug interactions
xUntreated thyroid dysfunction
xUncontrolled diabetes
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.
xUncontrolled diabetes or severe glucose dysregulation
xActive cancer or high cancer risk requiring caution with IGF-1 elevation
xPregnancy or breastfeeding
Decision Guide
Which isright for you?
Choose Tabimorelin if...
Stimulating growth hormone production in healthy individuals
Exploring GH secretagogue mechanisms in research settings
Patients preferring oral administration over injections
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