Levothyroxine (T4) vs Liothyronine (T3)

Side-by-side comparison of mechanisms, dosing, interactions, and stacking potential.

Levothyroxine (T4)Liothyronine (T3)
CategoryHormonesHormones
Standard Dose
Timing
Cycle Duration
Evidence LevelStrongStrong

Mechanism

Synthetic thyroxine used to replace or augment thyroid hormone in hypothyroid states.

Contraindications

  • Requires endocrine supervision and lab monitoring

Mechanism

Synthetic triiodothyronine that directly raises active thyroid hormone signaling.

Contraindications

  • Cardiac arrhythmia risk
  • Do not use without thyroid labs

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