T3 Cytomel

Liothyronine Sodium is the synthetic form of triiodothyronine (T3), the most metabolically active thyroid hormone produced by the human body. Unlike thyroxine (T4), which requires peripheral conversion to T3 before exerting metabolic effects, Liothyronine is immediately bioactive upon absorption. In clinical medicine, it is prescribed for hypothyroidism, myxedema coma, and thyroid suppression testing. In body composition research, it is the most potent pharmacological tool available for directly increasing metabolic rate.

T3 governs the basal metabolic rate of virtually every cell in the body. Its mechanism of action involves binding to nuclear thyroid hormone receptors (TRα and TRβ), which directly modulate gene transcription controlling mitochondrial activity, ATP production, oxygen consumption, and substrate metabolism. When exogenous T3 elevates circulating levels above baseline, the body's energy expenditure increases across all tissues — including skeletal muscle, cardiac muscle, hepatic tissue, and adipose tissue. This is not a selective fat-burning effect: T3 increases the catabolism of all macronutrient substrates (fats, proteins, and carbohydrates), which is why co-administration with anabolic agents is strongly recommended to preserve lean tissue.

T3 is the metabolic accelerator of choice for researchers who have plateaued in fat loss despite dietary and training optimization. It is frequently combined with Clenbuterol (for synergistic thermogenic effect), anabolic steroids (to counteract T3's catabolic effect on muscle), and/or growth hormone (which supports lipolysis and protein synthesis simultaneously). The combination of T3 + Clenbuterol + a moderate dose of anabolic steroid is one of the most widely documented cutting stacks in body composition research.

T3 is best suited for intermediate to advanced researchers who understand its dose-sensitivity and the importance of gradual titration. Because exogenous T3 suppresses endogenous thyroid hormone production via negative feedback on the hypothalamic-pituitary-thyroid (HPT) axis, abrupt discontinuation can result in temporary hypothyroidism. Novice researchers should exhaust dietary and training variables before introducing thyroid hormones. It is suitable for both male and female researchers.

Liothyronine has a half-life of approximately 2.5 days, though its metabolic effects are observed within hours of administration. Dosing is initiated at 25 mcg daily and increased by 12.5–25 mcg increments every 5–7 days, up to a typical maximum of 75–100 mcg daily. Tapering down (reverse of the ramp-up) is critical upon discontinuation to allow the HPT axis to gradually resume endogenous T3/T4 production. Administration without a taper can result in weeks of hypothyroid symptoms: fatigue, weight gain, cold sensitivity, and mental fog. T3 is not hepatotoxic. Co-administration with an anabolic steroid (even a mild one like Anavar at 20–40 mg) is advisable during the administration period to offset T3's non-selective catabolic tendency.