T3 (Liothyronine)

T3 enters target cells and binds to thyroid hormone receptors (TR-alpha and TR-beta) in the cell nucleus. These receptors are transcription factors that regulate the expression of hundreds of genes involved in metabolism. T3 increases: (1) Basal metabolic rate by upregulating mitochondrial oxidative phosphorylation and uncoupling protein expression; (2) Thermogenesis and heat production; (3) Protein synthesis (at physiological doses) and protein catabolism (at supraphysiological doses); (4) Lipolysis and fatty acid oxidation; (5) Glucose absorption and gluconeogenesis; (6) Heart rate and cardiac output via beta-adrenergic receptor upregulation; (7) Oxygen consumption across all tissues.

T3 is approximately 95% absorbed orally, with peak plasma levels at 2-4 hours. The half-life is 6-8 hours in euthyroid individuals (may be shorter in hyperthyroid and longer in hypothyroid states). Steady-state levels are reached within 2-3 days of consistent dosing. T3 is metabolized primarily through deiodination, conjugation, and deamination in the liver and kidneys. Exogenous T3 suppresses TSH and endogenous thyroid hormone production through negative feedback on the hypothalamus and pituitary.

• ✓Significant increase in basal metabolic rate (increases daily caloric expenditure by 200-400+ calories depending on dose)
• ✓Accelerated fat loss, especially when combined with caloric deficit
• ✓Enhanced fat oxidation and mobilization
• ✓Improved energy levels and mental clarity (at appropriate doses)
• ✓Synergistic with other fat loss compounds (clenbuterol, cardarine, anabolic agents)
• ✓Rapid onset of action (effects felt within 1-2 days)
• ✓Can help overcome metabolic adaptation during extended diets
• ✓Improved cholesterol and lipid profiles (thyroid hormone is a major regulator of cholesterol metabolism)

• ⚠Muscle catabolism if dose is too high or anabolic support is insufficient (T3 increases protein turnover; without adequate anabolic signaling, net muscle loss occurs)
• ⚠Increased heart rate and palpitations (dose-dependent)
• ⚠Anxiety, nervousness, and irritability at higher doses
• ⚠Insomnia and disrupted sleep
• ⚠Excessive sweating and heat intolerance
• ⚠Increased appetite (which can counteract fat loss if not managed)
• ⚠Tremors (especially hand tremors) at higher doses
• ⚠Potential bone density loss with chronic supraphysiological use (thyroid excess increases osteoclast activity)
• ⚠Temporary suppression of endogenous thyroid function (TSH suppression)
• ⚠Headaches during initial use
• ⚠Diarrhea at high doses

Contraindications

• 🚫Uncontrolled cardiac arrhythmias or significant cardiovascular disease
• 🚫Untreated adrenal insufficiency (T3 can precipitate adrenal crisis; cortisol must be adequate before starting thyroid hormone)
• 🚫Osteoporosis or significant bone density loss
• 🚫Thyrotoxicosis or hyperthyroidism
• 🚫Pregnant women (exogenous T3 crosses the placenta)
• 🚫Individuals with anxiety disorders (T3 exacerbates anxiety symptoms)

**No traditional PCT is required**, but a proper taper is essential. **Taper protocol:** - Reduce dose by 12.5-25 mcg every 3-5 days - Example taper from 50 mcg: 50 > 37.5 > 25 > 12.5 > off - Do NOT stop T3 abruptly at high doses; the thyroid needs time to resume production **Recovery:** - TSH typically normalizes within 2-6 weeks after cessation - Temporary hypothyroid symptoms (fatigue, cold sensitivity, slight weight gain) may occur during recovery - In healthy individuals, thyroid function always recovers; permanent thyroid damage from T3 cycles is a myth - Check TSH and Free T3/T4 at 4 weeks post-cycle to confirm recovery

• 1.ALWAYS pair T3 with an anabolic compound (testosterone, SARMs, at minimum) to prevent muscle loss; T3 alone during a cut will eat muscle
• 2.The appetite increase is real and can sabotage your cut; plan your meals in advance and use high-volume, low-calorie foods
• 3.Split dosing (AM/PM) provides smoother energy levels and fewer side effects than a single large dose
• 4.Monitor your resting heart rate; if it exceeds 100 bpm consistently, reduce the dose
• 5.T3 is best used for 4-8 week cutting cycles, not for chronic use
• 6.Do not exceed 75 mcg/day unless under medical supervision
• 7.The taper is important; abrupt discontinuation at high doses can cause a rebound hypothyroid state
• 8.T3 stacks exceptionally well with clenbuterol for a powerful fat loss combination
• 9.Keep protein intake very high (1.2-1.5g per lb bodyweight) to offset the catabolic effects
• 10.If you feel excessively anxious, jittery, or cannot sleep, your dose is too high; reduce immediately

1. [1]Jonklaas J, et al. (2014). Guidelines for the treatment of hypothyroidism. Thyroid.
2. [2]Celi FS, et al. (2011). Metabolic effects of liothyronine therapy in hypothyroidism. J Clin Endocrinol Metab.