Levothyroxine

Clinical safety rating: safe

Human studies have proved safety

How it works

Mechanism information is still being processed. Check the DailyMed link in the sidebar for the official prescribing information.

Dosing & administration

Dosing varies by indication and patient profile. Always follow your institution's current prescribing guidelines.

Renal impairment	Consult protocols for adjustment.
Liver impairment	Consult protocols for adjustment.

Use during pregnancy

1st trimester	Critical. Increase dose proactively (often by adding 2 extra doses/week at confirmation of pregnancy). Monitor TSH every 4 weeks.
2nd trimester	Safe. Continue dose adjustment guided by TSH. Target TSH <3.0 mIU/L.
3rd trimester	Safe. Maintain euthyroid state. Monitor TSH. Return to pre-pregnancy dose postpartum.

Clinical note

Essential in pregnancy. Maternal thyroid hormone is critical for fetal brain development, particularly in T1 before the fetal thyroid is functional (~12 weeks). Untreated hypothyroidism causes irreversible fetal neurodevelopmental impairment. Dose requirements increase by approximately 30–50% in T1 due to increased TBG, placental T4 metabolism, and hCG-driven thyroid stimulation. TSH targets in pregnancy: T1 <2.5 mIU/L, T2 and T3 <3.0 mIU/L (or institution-specific).

Breastfeeding

Safe. Levothyroxine is a natural hormone present in breast milk; supplementation does not cause any known adverse effects in the infant.

Warnings & precautions

When not to use it

weight loss

Drug interactions

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