Levothyroxine at a glance
Medicine class
Thyroid hormone replacement.
Available forms
Selected UK products include tablets, oral solutions and a hospital-administered injection or infusion.
Food and drink
Oral levothyroxine is best taken on an empty stomach before the first meal or caffeine-containing drink.
Blood tests
Thyroid blood tests check whether treatment remains appropriate.
What is Levothyroxine used for?
Licensed uses represented by selected UK products include:
Replacement treatment for congenital or acquired hypothyroidism, including hypothyroidism in children.
Diffuse non-toxic goitre and goitre associated with Hashimoto's thyroiditis, for selected oral solutions.
Thyroid-hormone suppression treatment in thyroid carcinoma, for selected oral solutions.
Myxoedema coma, using the injectable product in hospital.
Hypothyroidism when oral treatment is not feasible, using the injectable product.
How does Levothyroxine work?
Levothyroxine supplies thyroxine (T4). Body tissues convert some T4 into the more active hormone T3, which regulates metabolism, growth and other thyroid-dependent functions through nuclear thyroid receptors.
Levothyroxine preparations and strengths
Oral solution
Route: Oral
Strengths: 25 micrograms/5 mL, 50 micrograms/5 mL, 100 micrograms/5 mL, 125 micrograms/5 mL
Tablet
Route: Oral
Strengths: 25 micrograms, 50 micrograms, 100 micrograms
How to take Levothyroxine
Follow the directions for the specific product supplied.
Take oral levothyroxine on an empty stomach before the first meal or caffeine-containing drink.
Swallow tablets whole with water.
Measure oral solution with the supplied oral syringe or measuring device; do not use a household spoon.
Do not crush and disperse the selected tablet for a young child because inaccurate measurement may result; an authorised oral solution is preferable.
Injection or infusion is administered by healthcare professionals when oral treatment is not feasible.
Levothyroxine side effects
Common or expected effects
- Difficulty sleeping
- Headache
- Anxiety or restlessness
- Increased sweating
- Hair loss
Get urgent medical advice
- Swollen throat or tongue, itchy raised rash or difficulty breathing
- High temperature with a fast or irregular heartbeat, dizziness, fainting or jaundice
- Chest pain, marked palpitations or severe breathlessness
Levothyroxine in pregnancy
Levothyroxine can be used during pregnancy when needed. Established replacement treatment should not be stopped without prescriber advice. Tell the prescriber promptly and attend additional thyroid blood tests. Levothyroxine must not be combined with an antithyroid medicine as combination treatment for hyperthyroidism during pregnancy.
Levothyroxine while breastfeeding
Levothyroxine is generally compatible with breastfeeding. Only low concentrations enter breast milk during appropriate replacement treatment; check with a pharmacist or prescriber if there are concerns about the baby.
Levothyroxine interactions
Tell the prescriber or pharmacist about all medicines, supplements and herbal products. Important examples include:
Calcium, iron, aluminium-containing antacids, sucralfate and bile-acid sequestrants
These can reduce levothyroxine absorption; ask a pharmacist or prescriber for advice.
Proton-pump inhibitors, such as omeprazole
Reduced stomach acidity may lower levothyroxine absorption, so thyroid control may need reassessment.
Carbamazepine, phenytoin, barbiturates and rifampicin
These may increase levothyroxine clearance and reduce thyroid-hormone concentrations.
Common questions about Levothyroxine
Answers are fully visible for fast scanning and source review.
Why should levothyroxine be taken on an empty stomach?
Food can reduce or vary its absorption. Taking it consistently before the first meal helps produce more predictable thyroid-hormone levels.
Can I drink tea or coffee with levothyroxine?
Caffeine-containing drinks may interfere with absorption. Take levothyroxine before the first such drink.
Can levothyroxine be taken with calcium or iron?
Calcium and iron can reduce levothyroxine absorption. Ask a pharmacist or prescriber for advice.
Sources
These sources were used to prepare and review this medicine page.
Prepared and reviewed by the iatroX editorial team.