Thyroid Health

Key takeaways

• Levothyroxine is replacement treatment for an underactive thyroid; liothyronine has a more limited, specialist-directed role.
• Carbimazole and thiamazole reduce thyroid hormone production and require monitoring for uncommon but serious adverse effects.
• Switching product, changing dose or stopping treatment without review can destabilise thyroid control.

Listings are for comparison only; suitability and supply depend on clinician and pharmacy checks, blood-test results and prescription requirements.

How the medicine groups differ

Thyroid replacement includes levothyroxine and, in selected cases, liothyronine. Antithyroid medicines include carbimazole and thiamazole. Replacement and antithyroid medicines treat opposite hormone problems and are not substitutes for one another.

What these medicines are used for

Replacement medicines are used for hypothyroidism. Antithyroid medicines may be used for hyperthyroidism as part of a clinician-led plan.

Important safety checks

Tell the clinician about pregnancy or plans for pregnancy, heart disease and all medicines or supplements. Iron, calcium and some other products can affect thyroid hormone absorption. Blood tests are needed after relevant treatment changes; symptoms alone cannot confirm the correct dose.

When to seek urgent care

While taking an antithyroid medicine, fever, sore throat or mouth ulcers require urgent medical advice and a blood-count check. Seek emergency help for chest pain, severe breathlessness, fainting, marked confusion, a very fast or irregular heartbeat, or a serious allergic reaction.