Thyroid hormonePrescription only
Levothyroxine
Tablet
Quick Summary
Levothyroxine replaces the hormone the thyroid isn't making.
Hypothyroidism
After thyroid surgery
Medical Uses
Hypothyroidism: Lifelong replacement for most people.
After thyroid surgery: Replacement and cancer control.
How it's taken
Take every morning on an empty stomach with water, 30–60 minutes before breakfast or tea. Blood tests (TSH) guide the amount.
Your doctor decides the right dose for you and how long to take it.
Your doctor decides the right dose for you. Follow their instructions and the label.
Common Side Effects
Palpitations
If the amount is too high.
Sleep problems
Or anxiety if too high.
Few side effects
At the right amount.
Interactions
Calcium, iron and antacids
Take four hours apart.
Some epilepsy medicines
Change levels.
Critical Warnings
Pregnancy
Needs may increase; tell your doctor early.
Heart disease
Started cautiously.
Sources and further reading
Last updated 21 October 2026. For more detail, see these trusted health organisations.
- Levothyroxine: drug information(opens in a new tab) · MedlinePlus, US National Library of Medicine
- Levothyroxine: a medicine for an underactive thyroid (hypothyroidism)(opens in a new tab) · NHS