Drug class

Thyroid hormone replacements

Replace the hormone an underactive thyroid can't make on its own.

How it works

Levothyroxine is a synthetic version of T4, the main hormone your thyroid normally makes. The body converts it to active T3 as needed.

Hypothyroidism, certain thyroid cancers, post-thyroidectomy hormone replacement.

Most side effects mean the dose is too high: rapid heartbeat, anxiety, tremor, weight loss, trouble sleeping.

Take 30–60 minutes before breakfast on an empty stomach. Calcium, iron, and antacids cut absorption — separate by 4 hours.

Educational only. Not medical advice. Always confirm with your prescriber or pharmacist.