MK-677 vs TB-500
Well Studied vs Well Studied
compatible Researched · 90% Non-competing mechanisms enhancing recovery effects.
Molecular Data
MK-677 TB-500
Weight 624.77 Da 4,963.44 Da
Half-life ~24 hours ~2 hours
Chain — 43 amino acids
Type Non-peptide ghrelin receptor agonist Thymosin fragment
Key Benefits
MK-677
01 97% increase in 24-hour growth hormone secretion
02 40-72% elevation in IGF-1 levels
03 Enhanced sleep quality with improved REM patterns
04 Preferential lean tissue gains of 1.1-2.7kg over 8-12 months
05 15% basal metabolic rate increase within 2 weeks
06 Oral administration (no injections required)
TB-500
01 Superior systemic tissue repair
02 Accelerated muscle, tendon, and ligament healing
03 Enhanced cell migration and angiogenesis
04 Comprehensive regenerative effects
05 Neuroprotective properties
Dosing Protocols
MK-677
Start 12.5mg daily, increase to 25mg based on tolerance / Once daily, preferably at bedtime on empty stomach
TB-500
2-5mg per injection (higher doses for serious injuries) / 2-3x weekly (e.g., Monday, Wednesday, Friday)
General tissue repair 2-3mg 2x weekly
Serious injury recovery 4-5mg 3x weekly
Athletic enhancement 2-3mg 2x weekly
Chronic conditions 3-4mg 2-3x weekly
Maintenance 2mg 1-2x weekly
Post-surgical recovery 3-5mg 3x weekly
Side Effects
MK-677
Appetite stimulation (>50% of users)
Water retention (30-40%)
Lethargy (20-30%)
Fasting glucose elevation (5-15mg/dL)
Note on testosterone suppression: at doses up to 20 mg daily, MK-677 is unlikely to cause significant testosterone suppression on its own. Above 20 mg daily, the likelihood of suppression and other side effects (insulin resistance, water retention, lethargy) increases. The case report documenting 85.7% testosterone suppression involved co-administration with LGD-4033, a SARM known to be profoundly suppressive, making the SARM the likely primary driver of that suppression.
TB-500
Generally minimal side effects
Possible mild injection site reactions
Temporary fatigue in some users
Contraindications
Heart disease or congestive heart failure
Diabetes or pre-diabetes
Active cancer
Severe cardiovascular disease
Pregnancy or breastfeeding
Active cancer treatment (due to angiogenic effects)
Pregnancy or breastfeeding
Immunosuppressive medications (consult provider)
WADA prohibited for competitive athletes
Research Evidence
MK-677 TB-500
Status Well Studied Well Studied
References 7 studies 6 studies
Latest July 2024 November 2025
FDA Approved No No
This comparison is for educational and research purposes only. Consult a healthcare professional before use.