T3 (Cytomel)

Mechanism: Synthetic triiodothyronine (T3), the most active thyroid hormone. Directly increases basal metabolic rate, thermogenesis, and substrate utilization. Suppresses TSH and endogenous T4/T3 production via negative feedback.

Dosage:

• Replacement (on-cycle support): 25 mcg/day
• Enhancement (fat loss): 50-75 mcg/day for 6-8 weeks
• Contest prep (aggressive): 75-100 mcg/day (catabolic risk high without AAS)

Administration:

• Oral tablet, split into 2-3 doses/day (due to short half-life)
• Take first dose on waking; second dose midday; optional third dose afternoon

Key Notes:

• ALWAYS run with a testosterone base -- T3 is catabolic to muscle without anabolic support
• Increases metabolic rate dose-dependently: useful for breaking through fat-loss plateaus
• Suppresses TSH and endogenous T3/T4 production -- thyroid function recovers but takes 2-6 weeks after cessation
• Taper down when discontinuing (reduce by 12.5-25mcg every 5-7 days) -- avoids rebound hypothyroidism
• Monitor thyroid panel (TSH, FT3, FT4) during and 4-6 weeks after use
• GH use can improve natural T4-to-T3 conversion, potentially reducing the need for exogenous T3
• Symptoms of too-high dose: anxiety, tremors, rapid heart rate, excessive sweating, insomnia

Before adding T3, check whether the low reading is real; steroids suppress total T3 without thyroid disease: Low T3 on steroids? It is probably not hypothyroidism.