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.
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.
Clinical content reviewed by the BetterBuyRx clinical team.
Educational only. Not medical advice. Always confirm with your prescriber or pharmacist.