Levothyroxine

Sold as Synthroid, Levoxyl, Unithroid

Levothyroxine replaces or supplements thyroid hormone for people with an underactive thyroid (hypothyroidism). It is one of the most-prescribed medications in the US.

Compare prices →~$9.00 / mo (generic, NADAC)

What it treats

Hypothyroidism, thyroid hormone replacement, and management of certain thyroid cancers.

Typical dosing

Take 30–60 minutes before breakfast on an empty stomach with a full glass of water. Dose is individualized by weight and lab tests.

Side effects

Most side effects mean too much hormone: rapid heartbeat, anxiety, weight loss, tremor.

Interactions to know

Calcium, iron, antacids, and some cholesterol meds reduce absorption — separate by 4 hours.

Pregnancy & breastfeeding

Safe in pregnancy; dose often needs to increase.

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