Prescribing Guides
Levothyroxine Prescribing Guide for Indian Clinical Practice
Levothyroxine prescribing reference for Indian clinicians covering thyroid replacement dosing, absorption factors, monitoring and NEET PG pharmacology.
MedNext Editorial Team | 2026-08-01 | 8 min read
Levothyroxine Prescribing Guide for Indian Clinical Practice
Levothyroxine prescribing reference for Indian clinicians covering thyroid replacement dosing, absorption factors, monitoring and NEET PG pharmacology.
Levothyroxine is the standard treatment for hypothyroidism and the most commonly prescribed thyroid hormone preparation in India. Its narrow therapeutic index and numerous absorption interactions require careful prescribing and monitoring.
Clinical Pharmacology Overview
Levothyroxine (synthetic T4) is a prohormone that is peripherally converted to the active hormone triiodothyronine (T3) by deiodinase enzymes (primarily type 1 and type 2). T3 then binds to nuclear thyroid hormone receptors, modulating gene transcription to regulate metabolism, growth, and development.
Pharmacokinetics: Oral bioavailability is 40-80% (highly dependent on fasting state). Highly protein-bound (more than 99%) to thyroxine-binding globulin (TBG), transthyretin, and albumin. Half-life is 6-7 days (long half-life allows once-daily dosing and provides stable serum levels). Metabolised by deiodination, conjugation, and deamination.
Indian Brand Names
- Thyronorm (Abbott)
- Eltroxin (GSK)
- Thyrox (Macleods)
- Lethyrox (Sun Pharma)
- Thyroup (Torrent)
Approved Indications in Indian Clinical Practice
- Primary hypothyroidism (Hashimoto thyroiditis, post-surgical, post-radioiodine)
- Secondary/central hypothyroidism (pituitary TSH deficiency)
- TSH suppression therapy in differentiated thyroid carcinoma
- Myxoedema coma (IV levothyroxine)
- Congenital hypothyroidism (newborn screening and treatment)
- Subclinical hypothyroidism (when TSH is above 10 mIU/L or symptomatic)
Dosing in Adults
Full replacement (young, healthy adults): 1.6 mcg/kg/day. For a 60 kg adult, this is approximately 100 mcg/day.
Elderly or cardiac disease: start 12.5-25 mcg/day. Increase by 12.5-25 mcg every 4-6 weeks to target TSH.
Subclinical hypothyroidism: 25-50 mcg/day if treatment is decided upon.
TSH suppression (thyroid cancer): dose to achieve target TSH (often below 0.1 mIU/L in high-risk disease).
Myxoedema coma: 200-400 mcg IV loading dose, then 50-100 mcg IV daily (with IV hydrocortisone).
Administration: take on an empty stomach, 30-60 minutes before breakfast, with water only. Alternatively, take at bedtime 3 hours after last meal. Consistency of timing is crucial.
Important Drug Interactions
- Calcium supplements, iron supplements, antacids (aluminium/magnesium): reduce absorption -- separate by 4 hours
- Cholestyramine, colestipol: bind levothyroxine in the gut -- separate by 4 hours
- Proton pump inhibitors: may reduce absorption
- Carbamazepine, phenytoin, rifampicin: increase levothyroxine metabolism (may need dose increase)
- Oestrogens (OCP, HRT): increase TBG, may necessitate dose increase
- Soy products, coffee, dietary fibre: reduce absorption
- Warfarin: levothyroxine increases warfarin sensitivity
- Amiodarone: complex thyroid interactions (can cause both hypo- and hyperthyroidism)
Side Effects and Monitoring
Side effects are generally those of iatrogenic hyperthyroidism from over-replacement: palpitations, tachycardia, tremor, weight loss, insomnia, diarrhoea, anxiety, heat intolerance, angina, atrial fibrillation.
At correct doses, levothyroxine should cause no side effects as it is physiological replacement.
Monitoring: TSH at 6-8 weeks after initiation or dose change. Once stable, TSH every 6-12 months. In thyroid cancer, monitor TSH and thyroglobulin as appropriate. In pregnancy, monitor TSH every 4 weeks in the first half and at least once in the second half.
Special Populations
Pregnancy: Levothyroxine requirement increases by approximately 30-50% in pregnancy (increase dose as soon as pregnancy is confirmed in known hypothyroid patients). Target TSH in the first trimester: below 2.5 mIU/L (or trimester-specific reference range). Untreated maternal hypothyroidism is associated with adverse obstetric and neurodevelopmental outcomes.
Renal impairment: No dose adjustment needed.
Hepatic impairment: No specific dose adjustment. Monitor thyroid function.
Elderly and cardiac disease: Start low, go slow. Rapid replacement can precipitate angina, arrhythmias, or myocardial infarction.
Congenital hypothyroidism: 10-15 mcg/kg/day at birth. Early treatment (within 2 weeks) prevents intellectual disability.
NEET PG High-Yield Points
- T4 is a prohormone converted to active T3 by deiodinases
- Long half-life (6-7 days) allows once-daily dosing
- Highly protein-bound to TBG (changes in TBG affect total T4 but not free T4)
- Must be taken on empty stomach -- absorption impaired by food, calcium, iron, coffee
- Check TSH no sooner than 6 weeks after dose change (steady state)
- Dose increases needed in pregnancy (30-50% increase)
- Myxoedema coma: IV levothyroxine + IV hydrocortisone (give steroids before thyroid hormone to prevent adrenal crisis)
- Over-replacement risks: atrial fibrillation, osteoporosis (especially in postmenopausal women)
- Congenital hypothyroidism: cretinism if untreated -- newborn screening is essential
Indian Regulatory Status
Levothyroxine is a Schedule H drug under the Drugs and Cosmetics Act. It is included in the NLEM of India and is price-controlled under DPCO. Thyronorm (Abbott) and Eltroxin (GSK) are the two most widely prescribed brands in India. Available in a wide range of tablet strengths (12.5, 25, 50, 75, 88, 100, 112, 125, 150, 175, 200 mcg). Brand switching should be avoided where possible, or TSH should be rechecked 6 weeks after any brand change, as bioavailability can vary between manufacturers.
Frequently Asked Questions
Why must levothyroxine be taken on an empty stomach?
Levothyroxine absorption is reduced by approximately 20-40% when taken with food. The standard recommendation is to take it 30-60 minutes before breakfast (or at bedtime, at least 3 hours after the last meal). Coffee, calcium, iron, and soy products significantly impair absorption.
How long does it take for levothyroxine to reach steady state?
Due to its long half-life (6-7 days), levothyroxine takes 4-6 weeks to reach steady state after initiation or dose change. TSH should be rechecked no sooner than 6 weeks after any dose adjustment.
What is the usual starting dose?
In young, healthy adults: 1.6 mcg/kg/day (approximately 75-100 mcg/day for most adults). In elderly patients or those with cardiac disease: start low at 12.5-25 mcg/day and titrate slowly every 4-6 weeks. The goal is to normalise TSH.
Why is hypothyroidism common in India?
India has high rates of hypothyroidism due to iodine deficiency (despite universal salt iodisation), Hashimoto thyroiditis, and post-surgical/post-radioiodine causes. Studies suggest a prevalence of clinical and subclinical hypothyroidism of approximately 10-11% in the Indian population.
Continue reading
Prescribing GuidesMetformin Prescribing Guide for Indian Clinical Practice
Evidence-based metformin prescribing for Indian clinicians covering dosing, brands, interactions, monitoring and NEET PG high-yield points.
Prescribing GuidesCeftriaxone Prescribing Guide for Indian Clinical Practice
Complete ceftriaxone prescribing reference for Indian clinicians covering indications, dosing, reconstitution, drug interactions and NEET PG points.
Prescribing GuidesAmoxicillin Prescribing Guide for Indian Clinical Practice
Comprehensive amoxicillin prescribing reference for Indian doctors covering dosing, brands, resistance patterns and NEET PG high-yield pharmacology.
Continue with Prescribing Guides
Apply what you have read with clinical prescribing MCQs that test real decision-making: drug choice, dose selection, interactions and monitoring.
Try prescribing questionsBrowse all prescribing guides