Liothyronine (T3) vs MK-677
FDA Approved vs Well Studied
monitor Mechanism-based · 51% Both Liothyronine (T3) and MK-677 can raise blood pressure. Monitor BP regularly and consider adding cardiovascular support (cardarine, telmisartan, or similar).
Molecular Data
Liothyronine (T3) MK-677
Weight 650.97 Da 624.77 Da
Half-life ~1 day ~24 hours
Type Thyroid hormone (C15H12I3NO4) Non-peptide ghrelin receptor agonist
Key Benefits
Liothyronine (T3)
01 Direct and rapid increase in basal metabolic rate
02 Enhanced fat oxidation and lipolysis
03 Improved energy levels and reduction of hypothyroid fatigue
04 Faster-acting than T4 with effects noticeable within hours to days
05 Useful when peripheral T4-to-T3 conversion is impaired (illness, caloric deficit, stress)
06 Supports body temperature regulation and thermogenesis
07 Can improve cognitive clarity and reduce brain fog associated with low thyroid function
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)
Side Effects
Liothyronine (T3)
Tachycardia and palpitations (increased heart rate, especially at higher doses)
Anxiety, nervousness, and irritability
Insomnia and disrupted sleep architecture
Increased sweating and heat intolerance
Tremor (fine hand tremor, similar to hyperthyroid presentation)
Increased appetite despite accelerated metabolism
Loose stools or increased bowel frequency
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.
Contraindications
Untreated adrenal insufficiency (must correct cortisol deficiency before starting T3)
Acute myocardial infarction or unstable angina
Thyrotoxicosis or untreated hyperthyroidism
Known hypersensitivity to liothyronine or any tablet excipients
Uncorrected adrenal cortical insufficiency (risk of adrenal crisis)
Heart disease or congestive heart failure
Diabetes or pre-diabetes
Active cancer
Severe cardiovascular disease
Pregnancy or breastfeeding
Research Evidence
Liothyronine (T3) MK-677
Status FDA Approved Well Studied
References 5 studies 7 studies
Latest September 2023 July 2024
FDA Approved Yes No
This comparison is for educational and research purposes only. Consult a healthcare professional before use.