Euthyrox

Basic Euthyrox information

• INN (international nonproprietary name): Levothyroxine sodium
• Brand names available in the United Kingdom: Eltroxin, Euthyrox, Levothyroxine
• ATC code: H03AA01
• Forms and dosages: Oral tablets 25, 50, 75, 100, 125, 150, 175 and 200 mcg
• Manufacturers in the United Kingdom: Merck KGaA (Euthyrox) and generic manufacturers
• Registration status in the United Kingdom: Licensed by the MHRA; prescription-only medicine
• OTC / Rx classification: Prescription-only medicine (POM)

Legal status and availability in the UK

Euthyrox (levothyroxine) is a prescription-only medicine (POM) in the UK.

In our online pharmacy, Euthyrox is available without a prescription, with discreet delivery to the United Kingdom in 5‑14 days.

Product identity, classification and regulatory status

Active ingredient and ATC classification

Levothyroxine sodium is the active ingredient and the International Nonproprietary Name (INN).

The ATC code is H03AA01, which classifies systemic synthetic thyroxine (T4).

Formulations and strengths

Tablet strengths and colour‑coding

Euthyrox and other levothyroxine products are mainly oral tablets available in multiple strengths.

Common strengths include 25, 50, 75, 100, 125, 150, 175 and 200 mcg.

Licensed indications and typical dosing regimens

Primary hypothyroidism and replacement dosing

Euthyrox (levothyroxine) is indicated for thyroid hormone replacement in primary hypothyroidism.

Typical full replacement dosing in adults is around 1.6 mcg/kg/day given once daily.

Initial adult doses often start at 25–50 mcg once daily and are titrated every 4–6 weeks based on TSH.

Thyroid cancer suppression and special uses

Levothyroxine is used to suppress TSH in certain thyroid cancer patients; doses are individualised and usually higher than replacement doses.

These patients require specialist endocrine supervision and more frequent monitoring.

Special populations — children, elderly and pregnancy

Paediatric dosing and monitoring

Paediatric dosing is weight‑based and specialist supervised.

Neonates with severe hypothyroidism may start at higher weight‑based doses of approximately 10–15 mcg/kg/day initially and then titrate closely.

Children require frequent follow‑up and TSH monitoring during dose adjustments to support normal growth and development.

Elderly/cardiac precautions and pregnancy adjustments

Elderly patients and those with cardiovascular disease should start at low doses (12.5–25 mcg/day) due to increased cardiac sensitivity.

Increase doses cautiously with careful TSH monitoring to avoid precipitating angina or arrhythmias.

Pregnancy commonly necessitates dose increases and more frequent TSH checks because thyroid hormone requirements rise; obstetric liaison is recommended.

Dose adjustments, monitoring and follow‑up strategy

Titration timeline and TSH targets

Dose adjustments are guided primarily by serum TSH and, where appropriate, free T4 measurements.

Titration typically occurs every 4–6 weeks until stable levels are reached.

Full replacement aims for a normal TSH range; suppression therapy targets lower values as advised by an endocrinologist.

A TSH test should be requested after every dose change and at regular intervals once stable.

When to refer or adjust rapidly

Consider faster review or specialist referral if a patient develops chest pain, atrial fibrillation, rapid weight loss or other signs of over‑replacement.

Also review dosing when pregnancy, major weight change, ageing or interacting medications occur.

Administration tips and key drug interactions

Best practices for taking levothyroxine

Take levothyroxine on an empty stomach 30–60 minutes before breakfast for best and most consistent absorption.

Alternatively, many patients take it at least 3–4 hours after an evening meal if morning dosing is impractical.

Keeping the dosing time consistent day‑to‑day helps maintain steady thyroid levels.

Common interacting substances to avoid around dosing

Avoid calcium supplements, iron, aluminium‑containing antacids and sucralfate near the time of dosing as they reduce absorption.

Certain multivitamins and bile acid sequestrants can also interfere with uptake.

Oestrogen therapy and some contraceptives may alter thyroid‑binding protein levels and change replacement requirements.

These agents should be separated by at least 3–4 hours from levothyroxine dosing.

Contraindications, cautions and safety flags

Absolute contraindications

Absolute contraindications include untreated thyrotoxicosis and untreated adrenal insufficiency.

Administration is also contraindicated in recent or ongoing acute myocardial infarction and in patients with a known hypersensitivity to levothyroxine or tablet excipients.

Relative cautions: cardiac, adrenal and bone health

Exercise caution in patients with coronary artery disease, diabetes or osteoporosis risk; long‑term high doses can worsen bone loss.

Frail elderly patients need lower starting doses and slow titration.

Red flags: rapid heartbeat, chest pain or severe anxiety should trigger immediate medical assessment.

Side effects, overdose signs and patient reporting

Common adverse effects and their mechanisms

Most adverse effects reflect over‑replacement and mimic features of hyperthyroidism.

Common mild effects include headache, nervousness, insomnia and mild tremors.

More notable effects include palpitations, tachycardia, heat intolerance, diarrhoea and menstrual changes.

These symptoms often indicate the dose is too high and should prompt a review rather than stopping medication suddenly.

Overdose response and emergency advice

Overdose can cause chest pain, rapid heartbeat, tremors and confusion and requires urgent medical attention.

Suspected adverse reactions can be reported via the Yellow Card scheme; seek immediate help for severe symptoms.

Missed dose advice: take as soon as remembered unless it is near the next dose; never double dose.

Storage

Storage conditions

Store levothyroxine at 20–25°C, protected from light, moisture and heat.

Keep tablets in original packaging or blister packs where provided to reduce degradation.

Store the medicine away from bathrooms and windows to avoid moisture and heat.

Generic vs brand switching and bioequivalence

Clinical impact of switching brands

Clinical guidance and experience stress consistent use of the same levothyroxine brand where possible because small differences in bioavailability can alter TSH.

Patients often report fluctuating thyroid tests or symptoms after a switch even when products meet regulatory bioequivalence criteria.

A TSH check after any brand substitution is advisable to confirm therapeutic stability.

Practical points when switching brands

Patients who are stable on a specific brand can ask to stay on it, and should note batch numbers if issues arise.

Counselling points

Key counselling points

Know the active ingredient (levothyroxine sodium), the strength and the dosing time.

Take it on an empty stomach 30–60 minutes before breakfast and separate calcium or iron by several hours.

Know the common interactions, the storage instructions and the missed‑dose guidance.

Tell your prescriber about pregnancy, cardiac disease and current medicines.

Arrange a TSH test after any brand switch or dose change and report adverse effects via the Yellow Card scheme.

Delivery across the United Kingdom