Levothyroxine: Uses, Side Effects, and How to Take It
Levothyroxine is a prescription thyroid hormone that replaces the hormone your body is not making enough of or cannot use properly. It is used to treat hypothyroidism and, in some cases, to slow or shrink an enlarged thyroid or thyroid cancer.
Take levothyroxine exactly as prescribed, usually on an empty stomach and at the same time each day. Do not change your dose or stop treatment without medical guidance, because too much or too little thyroid hormone can cause serious problems.
Key facts at a glance
- ATC
- H03AA01
- Generic
- Levothyroxine
- Class
- thyroid-hormone
- Brands
- —
- Availability
- rx
- Pregnancy
- A
- Half-life (h)
- 168
- Routes
- oral
- Forms
- —
- Regions
- —
- Monitoring
- —
This page is for informational purposes only.
Do not use this information to diagnose yourself or to replace a physician's advice. Always consult a qualified healthcare provider before starting, stopping, or changing any medication. If you believe you are experiencing a medical emergency, call your local emergency number immediately.
Dosage and administration
- Usual dose
- 25 to 50 mcg once daily
- Maximum
- consult physician
- Frequency
- once daily
- Instructions
- Follow physician instructions
- Duration limits
- as prescribed
- Monitoring
- standard
- Usual dose
- 2 to 3 mcg per kg once daily
- Maximum
- consult physician
- Frequency
- once daily
- Instructions
- Follow physician instructions
- Duration limits
- as prescribed
- Monitoring
- standard
- Usual dose
- 12.5 to 25 mcg once daily
- Maximum
- consult physician
- Frequency
- once daily
- Instructions
- Follow physician instructions
- Duration limits
- as prescribed
- Monitoring
- standard
Overdose information
Special Populations
8 groupspregnancy
first trimesterincrease dose by 30-50%
continue levothyroxine therapy as untreated hypothyroidism poses greater risk to fetus; dose increase typically required
monitor TSH every 4 weeks during first trimester
pregnancy
second trimestermaintain adjusted dose
continue therapy with adjusted dose; do not discontinue
monitor TSH every 4-6 weeks
pregnancy
third trimestermaintain adjusted dose
continue therapy; may require further adjustment based on TSH
monitor TSH at least once in third trimester
lactation
breastfeedingno adjustment needed
continue levothyroxine therapy while breastfeeding; minimal transfer to breast milk
monitor infant thyroid function if concerns
pediatric_age
neonates infantsweight-based dosing starting at 10-15 mcg/kg/day
initiate at lower dose and titrate gradually; crush tablets and administer with small amount of water
monitor TSH and T4 every 4-6 weeks until stable, then every 6-12 months
geriatric
elderly 65start at 25-50 mcg daily
initiate at lowest effective dose and titrate slowly; increased cardiovascular risk in elderly
monitor TSH after 6-8 weeks of dose change; monitor for cardiac symptoms
Use with caution and monitor for adverse effects.
renal_impairment
severe renalmay require dose reduction in severe impairment
use cautiously in end-stage renal disease; may need dose reduction
monitor TSH and adjust dose as needed
hepatic_impairment
any degreeno specific adjustment needed
standard dosing; metabolism may be slightly altered
monitor TSH and adjust dose as needed
Statistics and clinical data
Commonly prescribed since
Levothyroxine was first approved by the FDA in the 1950s for treatment of hypothyroidism
Rank among most prescribed medications in US
Levothyroxine is consistently among the most commonly prescribed prescription medications in the United States
Primary therapeutic use
Primary indication is replacement therapy for diminished or absent thyroid hormone production
Drug classification
Classified under thyroid hormones in the ATC system
Contraindications
Conditions and patient states where this medication should be avoided or used with caution.
Do not use (1)
Known allergy to this medication or its components
Use caution (1)
Consult healthcare provider for benefits vs risks assessment
Official drug label
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This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 24, 2026. · Read our editorial policy