Sounds like 'lee-voe-thye-ROX-een'

Easy-to-read medicine information about levothyroxine– what it is, how to take levothyroxine safely and possible side effects.

Type of medicine Also called
  • Thyroid hormone
  • Eltroxin®
  • Synthroid®

What is levothyroxine?

  • Levothyroxine is a replacement hormone when your body cannot make enough thyroid hormone - a condition called hypothyroidism
  • It is also used to treat other types of thyroid disorders such as certain types of goiters, and thyroid cancer. 


  • The dose of levothyroxine will be different for different people. It depends on your age, weight, medical condition, laboratory test results and your response to treatment.
  • Always take your levothyroxine exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much levothyroxine to take, how often to take it, and any special instructions.

How to take levothyroxine

  • Levothyroxine is best taken in the morning, on an empty stomach, about 30 minutes or 1 hour before breakfast.
  • If this is too much of a hassle for you, and you end up missing your medicine, it is better to just take it whenever you want, and your doctor can increase the dose if needed. Speak to your doctor.
  • Take levothyroxine with a full glass of water. 
  • There are different brands of levothyroxine tablets. Do not swap or change brands without checking with your doctor of pharmacist. If you are unsure of the brand you are taking, ask your doctor or pharmacist.
  • If you forget to take a dose, take it as soon as you remember if it is still within 2 or 3 hours of your usual time. If it is longer than this before you remember, skip the forgotten dose. Do not take two doses together to make up for a missed dose.
  • Keep taking levothyroxine. It takes about 1 to 2 weeks to start working and may be 6 to 8 weeks before you feel the full effects of levothyroxine.
  • Do not stop taking levothyroxine; speak to your doctor or nurse before stopping. Levothyroxine is usually taken for life.

Possible side effects

Like all medicines, levothyroxine can cause unwanted side effects, although not everyone gets them. Often unwanted side effects improve as your body gets used to the new medicine.

Side effects What should I do?
  • Hair loss
  • This usually happens during the first few months of treatment and will stop once  your body gets used to the medication.
  • Tell your doctor if this continues or gets worse. 
  • Feeling sick or nausea
  • Headache
  • Tell your doctor if troublesome.
  • Feeling restless
  • Increased sweating
  • Feeling flushed or hot 
  • Feeling nervous or mood swings 
  • Tell your doctor 
  • Signs of an allergic reaction such as skin rash, itching, blisters, peeling skin, swelling of the face, lips, mouth or have problems breathing
  • Tell your doctor immediately or ring HealthLine.
  • Fast or irregular heart beat
  • Chest pain
  • Shortness of breath
  • Difficulty breathing
  • Tell your doctor immediately or ring HealthLine.


  • Levothyroxine can interact with a number of medicines and herbal supplements so check with your doctor or pharmacist before starting levothyroxine or before starting any new medicines..
  • Levothyroxine can interact with antacids, or medicines used for indigestion, iron supplements and calcium supplements. If you are taking any of these medicines, separate them from levothyroxine by at least 4 hours.

Learn more

Medsafe Consumer Information Sheets:


New Zealand Formulary Patient Information: levothyroxine


  1. Levothroxine sodium New Zealand Formulary (accessed August 2016)
  2. Levothyroxine (Eltroxin) Patient Info, UK (accessed August 2016)
  3. Management of thyroid dysfunction in adults BPAC, December 2010
Credits: Sandra Ponen, Pharmacist. Reviewed By: Dr J Bycroft, GP