DRUG OF THE DAY
levothyroxine
Synthetic thyroxine (T4) thyroid hormone
Before opening the card, recall one use, one safety check and one counseling point.
Reveal the drug learning card
Names and formulations
- Synthroid: oral tablet
Levothyroxine has a narrow dosing margin; keep the product, timing, and administration consistent and recheck TSH after clinically meaningful dose or product changes.
Common use
Replacement therapy for primary, secondary, or tertiary hypothyroidism and TSH suppression in selected differentiated thyroid cancer settings.
Mechanism of action
Provides synthetic T4, which is converted in tissues to active T3 and binds nuclear thyroid receptors to regulate gene transcription and metabolism.
Important adverse effects and monitoring
- Boxed warning: thyroid hormones are not for obesity treatment or weight loss; high doses can cause serious or life-threatening toxicity.
- Monitor TSH and, when indicated, free T4; over-replacement can cause atrial fibrillation, angina, and bone loss.
- Dose needs change with age, pregnancy, absorption, interacting drugs, and clinical status.
Patient counseling
- Take on an empty stomach 30–60 minutes before breakfast with water, consistently each day.
- Separate calcium or iron supplements by at least 4 hours and tell the prescriber before switching products.
Interaction to recognize
With: calcium carbonate, ferrous sulfate, and other binding agents
Why it matters: Can reduce levothyroxine absorption and raise TSH.
Practical response: Separate administration by at least 4 hours and monitor thyroid function when clinically indicated.
Check the original sources
- DailyMed — Synthroid (levothyroxine) prescribing information
Sections: Boxed Warning; 1 Indications and Usage; 2 Dosage and Administration; 5 Warnings and Precautions; 7 Drug Interactions; 12.1 Mechanism of Action; 17 Patient Counseling Information. Source checked 2026-09-13.
Selected learning points; verify current labeling for the complete prescribing information.