Levothyroxine
Thyroid Hormone (T4)- Drug Class
- Thyroid Hormone (T4)
- Mechanism of Action (MOA)
- Synthetic T4 → converted peripherally to active T3 → restores the euthyroid metabolic state.
- Black Box Warning
- Not for the treatment of obesity or weight loss — ineffective in euthyroid patients, and large doses can cause serious or life-threatening toxicity, especially with sympathomimetic (anorectic) amines.
- Clinical Notes
- Hypothyroidism. Take on an empty stomach ½–1 h before breakfast, separate from calcium/iron. Over-replacement → AFib/↓ bone density. Recheck TSH in 4–6 weeks.
- Source
- FDA label
Sources
Reviewed September 2026- FDA label — FDA / DailyMed
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