Euthyrox (Levothyroxine): Uses, Safety and Interactions

Uses and product scope

Euthyrox 25 micrograms is an oral tablet containing levothyroxine sodium, a manufactured form of the thyroid hormone T4. Its main purpose is replacement treatment for an underactive thyroid. The cited US label also includes specialist TSH suppression in certain differentiated thyroid cancers; this must not be generalised to every thyroid condition or every national authorisation. This page concerns tablets, not injectable levothyroxine or emergency treatment of myxoedema coma. Thyroid hormone is not a weight-loss medicine.

Monitoring and possible adverse effects

A suitable dose depends on thyroid tests, age, the cause of hypothyroidism, other illnesses and accompanying medicines. Levothyroxine has a narrow therapeutic range, so both too little and too much can cause problems. Excess exposure may produce palpitations, tremor, sweating, diarrhoea, anxiety or sleep disturbance. Chest pain or a new rapid or irregular heartbeat needs prompt assessment, especially in someone with heart disease. Untreated adrenal insufficiency must be addressed before replacement is started. Changes between levothyroxine products may require closer clinical and laboratory monitoring.

Food and medicine interactions

Food, calcium, iron, antacids and bile-acid binding medicines can reduce or alter absorption. A pharmacist can help plan consistent administration and separation according to the specific local leaflet; the intervals are not identical in every cited label. Proton pump inhibitors and orlistat may also affect thyroid control. Warfarin response and diabetes treatment requirements can change as thyroid status is corrected. Amiodarone, certain antiseizure medicines and some cancer treatments can alter hormone handling or thyroid function. Tell the prescriber about medicines started or stopped rather than adjusting Euthyrox independently.

Pregnancy and breastfeeding

Appropriate thyroid replacement is important during pregnancy, and requirements may increase. The US label advises that Euthyrox should not be discontinued simply because pregnancy occurs; prompt thyroid testing and prescriber-led review are needed. Levothyroxine is present in human milk, and treatment decisions during breastfeeding should consider maternal need and infant context. The cited US and South African information supports a product-specific overview; it does not establish that all national Euthyrox formulations or approved indications are identical.

Sources

• Euthyrox levothyroxine sodium tablets — US prescribing information — Provell; US PI revised April 2022; DailyMed SPL version 10 updated 27 January 2026
• Euthyrox 25, 50, 75 and 100 microgram tablets — approved South African professional information — Merck; SAHPRA approval 23 July 2024; CCDS version 8.0

Source check: 30 October 2026. This records a source check, not a clinical review by a doctor or pharmacist. Follow the current leaflet supplied with your medicine and seek professional advice for personal treatment.