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Levothyroxine

Euthyrox, L-Thyroxin Serb, Levohelm, Syntroxine · ATC code H03AA01

Also known as: Levothyroxin, Levotiroksin, Levotiroxina, Lévothyroxine · Brand names: Eferox, Euthyrox, L-Thyrox, L-Thyroxin, Levohelm, Levothyroxin Abdi, Levothyroxine Sodium, Tirosint, L-Thyroxin Serb, Syntroxine, Thyrex, Levipomix, Levotiron, Tefor Duotab, Votryxe

Key facts
Active substance
Levothyroxine
Drug class
Thyroid hormone
ATC code
H03AA01
Authorisation
authorised nationally; no central EU authorisation
Information as of
2026-11-03

Boxed warning

Thyroid hormones, including levothyroxine sodium tablets, either alone or with other therapeutic agents, should not be used for the treatment of obesity or for weight loss.

In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction.

Larger doses may produce serious or even life-threatening manifestations of toxicity, particularly when given in association with sympathomimetic amines such as those used for their anorectic effects [see Adverse Reactions (6), Drug Interactions (7.7), and Overdosage (10)].

Key facts

Levothyroxine is synthetic thyroxine (T4), an oral thyroid hormone. Per the US label it is used as replacement therapy in hypothyroidism and for TSH suppression in well-differentiated thyroid cancer, in adults and children including neonates.

What it is used for

  • Primary, secondary and tertiary, congenital or acquired hypothyroidism (adults and pediatric patients, including neonates)
  • Adjunct to surgery and radioiodine for TSH suppression in thyrotropin-dependent well-differentiated thyroid cancer
  • Not indicated for benign thyroid nodules or nontoxic goiter in iodine-sufficient patients, or for the recovery phase of subacute thyroiditis

Dosing

  • Once daily on an empty stomach, one-half to one hour before breakfast; at least 4 hours apart from drugs that impair absorption
  • Adults: full replacement dose 1.6 mcg/kg/day; titrate by 12.5 to 25 mcg every 4 to 6 weeks to a normal TSH
  • Elderly, cardiac disease or risk of atrial fibrillation: lower starting dose (less than 1.6 mcg/kg/day), titrate every 6 to 8 weeks
  • Children: weight-based by age, e.g. 10 to 15 mcg/kg/day at 0 to 3 months, 1.6 mcg/kg/day once growth and puberty are complete; titrate every 2 weeks
  • Secondary/tertiary hypothyroidism: titrate to free T4 in the upper half of the normal range, not TSH
  • Doses above 200 mcg/day are seldom required; peak effect may take 4 to 6 weeks
  • Stop biotin at least 2 days before TSH/T4 testing

Contraindications

  • Uncorrected adrenal insufficiency

Important warnings

  • Boxed warning: not for obesity or weight loss; larger doses can cause serious or life-threatening toxicity, especially with sympathomimetic amines
  • Narrow therapeutic index: over- or undertreatment affects the heart, bone, growth and metabolism
  • Elderly and cardiovascular disease: overtreatment may precipitate angina or arrhythmias; start low
  • Treat adrenal insufficiency with glucocorticoids first (risk of acute adrenal crisis)
  • Oral tablets not recommended for myxedema coma; may worsen glycemic control; over-replacement lowers bone mineral density

Side effects

  • Mainly signs of hyperthyroidism from overdosage: palpitations, tachycardia, arrhythmias, angina
  • Weight loss, heat intolerance, sweating, tremor, nervousness, insomnia, headache
  • Diarrhea, hair loss, menstrual irregularities, decreased bone mineral density
  • Children: pseudotumor cerebri, slipped capital femoral epiphysis; craniosynostosis and premature epiphyseal closure with overtreatment

Interactions

  • Calcium carbonate, ferrous sulfate, phosphate binders, bile acid sequestrants: separate by at least 4 hours; PPIs, sucralfate, antacids, orlistat may reduce absorption
  • Phenobarbital and rifampin increase levothyroxine metabolism; tyrosine kinase inhibitors such as imatinib may cause hypothyroidism
  • Increases the effect of oral anticoagulants; may reduce digitalis effect; may raise antidiabetic requirements
  • Ketamine (hypertension, tachycardia), sympathomimetics, tricyclic antidepressants; soy, fiber, walnuts and grapefruit juice affect absorption

Pregnancy and breastfeeding

  • No increased rate of major birth defects or miscarriage reported; should not be discontinued in pregnancy
  • Requirements may increase: check TSH as soon as pregnancy is confirmed, then every 4 weeks until the dose is stable; return to the pre-pregnancy dose after delivery
  • Present in human milk; no adverse effects on breastfed infants reported

Summary of the official product information, written with AI on 2026-11-03. Every number was checked automatically against the original text. Not reviewed by a physician – the full official text is authoritative.

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For patients

Patient information (US)

This product has no separate US patient information.

Authorisation and brand names by country

Medicines with exactly this active-substance composition, as listed in the national registers – alphabetical and without ranking. Whether a product is currently available is not shown here.

Germany

  • EferoxAristo Pharma Gmbh (Art 57) · 4 register entries
  • EuthyroxMerck Healthcare Germany Gmbh · 1 register entry
  • L-ThyroxHexal Ag · 1 register entry
  • L-Thyroxin1 A Pharma Gmbh, Sanofi-Aventis Deutschland Gmbh, Ratiopharm Gmbh, Zentiva Pharma Gmbh, Abz-Pharma Gmbh, Betapharm Arzneimittel Gmbh, Serb Sa, Aliud Pharma Gmbh, Berlin-Chemie Ag · 26 register entries
  • LevohelmHelm Pharmaceuticals Gmbh · 1 register entry
  • Levothyroxin AbdiAbdi Farma, Unipessoal Lda · 1 register entry
  • Levothyroxine Sodium1 A Pharma Gmbh · 1 register entry
  • TirosintIbsa Farmaceutici Italia · 2 register entries

Source: EMA – Article 57 product data (EU/EEA), as of 2026-11-03

Austria

  • EuthyroxMerck Gesellschaft Mbh · 1 register entry
  • L-Thyroxin SerbSerb Sa · 1 register entry
  • LevohelmHelm Pharmaceuticals Gmbh · 1 register entry
  • SyntroxineIbsa Farmaceutici Italia · 2 register entries
  • ThyrexSandoz Gmbh · 1 register entry

Source: EMA – Article 57 product data (EU/EEA), as of 2026-11-03

Turkey

  • EuthyroxMERCK İLAÇ ECZA VE KİMYA TİC. A.Ş. · 8 register entries
  • LevipomixVEM İLAÇ SAN. VE TİC. A.Ş. · 2 register entries
  • LevotironABDİ İBRAHİM İLAÇ SAN. VE TİC. A.Ş. · 16 register entries
  • Tefor DuotabVLD DANIŞMANLIK TIBBİ ÜRÜNLER VE TANITIM HİZMETLERİ LTD. ŞTİ. · 1 register entry
  • TirosintIBSA İLAÇ SAN. VE TİC. LTD. ŞTİ. · 12 register entries
  • VotryxeSABA İLAÇ SAN. VE TİC. A.Ş. · 16 register entries

Source: TİTCK – Ruhsatlı Beşeri Tıbbi Ürünler Listesi, as of 2026-11-03

Brand names in 27 more European countries
Belgium
Euthyrox
Bulgaria
Accu-Thyrox, L-Тироксин, Еутирокс
Croatia
Euthyrox
Cyprus
Accu-Thyrox, Euthyrox, T4, Thyrofix
Czechia
Althyxin, Euthyrox, Letrox, Synotirex, Syntroxine
Denmark
Eltroxin, Euthyrox, Levothyroxinnatrium "serb", Medithyrox, Striroxin, Tirosint, Tirosintsol
Estonia
L-Thyroxin Berlin-Chemie
Finland
Levothyroxine Orion, Levothyroxine Sandoz, Levothyroxine Serb, Medithyrox, Striroxin, Thyroxin Orion Corporation
France
L-Thyroxin Henning, L-Thyroxine, Levothyrox, Levothyroxine Abdi Farma, Levothyroxine Helm, Tcaps, Thyrofix, Tsoludose
Greece
Accu-Thyrox, Euthyrox, Izifet, Levo-4, Medithyrox, Medithyrox, T4, Thyro-4, Thyrohormone, Tirosint, Tirosol®
Hungary
Euthyrox, L-Thyroxin Henning, Letrox, Synotirex, Syntroxine
Iceland
Euthyrox, Levaxin, Thyrofix
Ireland
Eltroxin, Levothyroxine Amdipharm Limited, Levothyroxine Rowex, Levothyroxine Sodium Rowex, Levothyroxine Teva
Italy
Eutirox, Levotiroxina Abdi, Levotirsol, Tiche, Tifactor, Tirosint
Latvia
Euthyrox, L-Thyroxin Berlin-Chemie, Levothyroxine Sodium Berlin-Chemie, Levothyroxine Sodium Unifarma
Lithuania
L-Thyroxin Berlin-Chemie, Levothyroxine Sodium
Luxembourg
Euthyrox
Malta
Levothyroxine Sodium Renata Pharmaceuticals (Ireland), T4, Thyrofix
Netherlands
Eltroxin, Euthyrox, Levothyroxine Abdi, Levothyroxine Accord, Levothyroxine Natrium Uni-Pharma, Levothyroxine Nycomed, Levothyroxine Serb, Levothyroxinenatrium Teva, Thyrax Duotab, Thyrofix, Tirosint
Norway
Euthyrox, Levaxin, Levothyroxine Sodium Serb, Levotyroksinnatrium Sandoz, Tirosintsol
Poland
Althyxin, Eferox, Eltroxin, Euthyrox N, Letrox, Medithyrox, Tirosint Sol
Portugal
Eutirox, Letter, Levotiroxina Sódica Ratiopharm, Thyrofix
Romania
Accu-Thyrox, Euthyrox
Slovakia
Euthyrox, L-Thyroxin, Tirosint, Tirosintsol
Slovenia
Euthyrox
Spain
Eutirox, Levotiroxina Sanofi, Levotiroxina Sódica Teva, Solsint, Thyrofix
Sweden
Euthyrox, Levaxin, Levothyroxine Serb, Medithyrox, Striroxin, Tirosintsol

EMA – Article 57 product data (EU/EEA), 2026-11-03

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Sources

  1. U.S. Food and Drug Administration. Levothyroxine Sodium (Lupin Pharmaceuticals, Inc.) – Prescribing Information, 2025-03-19. DailyMed (NLM), 2026-11-03. https://dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=18717e58-89fb-4e2f-93b6-d6ac3e988d37
  2. EMA – Article 57 product data (EU/EEA), 2026-11-03. https://www.ema.europa.eu/en/human-regulatory-overview/post-authorisation/data-medicines-iso-idmp-standards-post-authorisation/public-data-article-57-database
  3. EMA – Article 57 product data (EU/EEA), 2026-11-03. https://www.ema.europa.eu/en/human-regulatory-overview/post-authorisation/data-medicines-iso-idmp-standards-post-authorisation/public-data-article-57-database
  4. TİTCK – Ruhsatlı Beşeri Tıbbi Ürünler Listesi, 2026-11-03. https://www.titck.gov.tr/dinamikmodul/85
  5. Wikidata (CC0): ATC H03AA.

Editorial: Medelix editorial team · last updated 2026-11-03 · How these pages are made · Report an error

Source: U.S. Food and Drug Administration (FDA), prescribing information, via DailyMed (NLM); public domain. Not advertising, not a treatment recommendation. For questions about your own treatment, ask your doctor or pharmacist.