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Uses|Precautions & warnings|Side effects|Interactions|Dosage


What is levothyroxine used for?

Levothyroxine is used to treat an underactive thyroid (hypothyroidism). It replaces or provides more thyroid hormone, which is normally produced by the thyroid gland. Low thyroid hormone levels can occur naturally or when the thyroid gland is injured by radiation/medications or removed by surgery. Having enough thyroid hormone is important for maintaining normal mental and physical activity. In children, having enough thyroid hormone is important for normal mental and physical development.

This medication is also used to treat other types of thyroid disorders (such as certain types of goiters, thyroid cancer).

This medication should not be used to treat infertility unless it is caused by low thyroid hormone levels.

How should I take levothyroxine?

Take this medication by mouth as directed by your doctor, usually once daily on an empty stomach, 30 minutes to 1 hour before breakfast. Take this medication with a full glass of water unless your doctor directs you otherwise.

If you are taking the capsule form of this medication, swallow it whole. Do not split, crush, or chew. People who cannot swallow the capsule whole (such as infants or small children) should use the tablet form of the medication.

For infants or children who cannot swallow whole tablets, crush the tablet and mix in 1 to 2 teaspoons (5 to 10 milliliters) of water, and give using a spoon or dropper immediately. Do not prepare a supply in advance or mix the tablet in soy infant formula. Consult your pharmacist for more information.

Dosage is based on your age, weight, medical condition, laboratory test results, and response to treatment.

Use this medication regularly in order to get the most benefit from it. To help you remember, take it at the same time each day.

Do not stop taking this medication without first consulting with your doctor. Thyroid replacement treatment is usually taken for life.

There are different brands of levothyroxine available. Do not change brands without first consulting your doctor or pharmacist.

Certain medications (cholestyramine, colestipol, colesevelam, antacids, sucralfate, simethicone, iron, sodium polystyrene sulfonate, calcium supplements, orlistat) can decrease the amount of thyroid hormone that is absorbed by your body. If you are taking any of these drugs, separate them from this medication by at least 4 hours.

Symptoms of low thyroid hormone levels include tiredness, muscle aches, constipation, dry skin, weight gain, slow heartbeat, or sensitivity to cold. Tell your doctor if your condition worsens or persists after several weeks of taking this medication.

How do I store levothyroxine?

Levothyroxine is best stored at room temperature away from direct light and moisture. To prevent drug damage, you should not store levothyroxine in the bathroom or the freezer. There may be different brands of levothyroxine that may have different storage needs. It is important to always check the product package for instructions on storage, or ask your pharmacist. For safety, you should keep all medicines away from children and pets.

You should not flush levothyroxine down the toilet or pour them into a drain unless instructed to do so. It is important to properly discard this product when it is expired or no longer needed. Consult your pharmacist for more details about how to safely discard your product.

Precautions & warnings

What should I know before using levothyroxine?

Before using this drug, tell your doctor if:

  • You are pregnant or breastfeeding. This is because, while you are expecting or feeding a baby, you should only take medicines on the recommendation of a doctor.
  • You are taking any other medicines. This includes any medicines you are taking which are available to buy without a prescription, such as herbal and complementary medicines.
  • You have allergy with any of active or inactive ingredients of levothyroxine or other medications.
  • You have any other illnesses, disorders, or medical conditions.

If you take an antacid, calcium carbonate (Tums), cholestyramine (Questran), colesevelam (Welchol), colestipol (Colestid), iron, orlistat (Alli, Xenical), simethicone (Phazyme, Gas X), sevelamer (Renvela, Renagel), sodium polystyrene sulfonate (Kayexalate), or sucralfate (Carafate), take it at least 4 hours before or 4 hours after you take levothyroxine.

Tell your doctor if you have or have ever had diabetes; hardening of the arteries (atherosclerosis); kidney disease; liver disease or hepatitis; bleeding problems; porphyria (condition in which abnormal substances build up in the blood and cause problems with the skin or nervous system); cardiovascular disease such as high blood pressure, chest pain (angina), arrhythmias, or heart attack; an underactive adrenal or pituitary gland, or any condition that makes it difficult for you to swallow.

Tell your doctor if you are pregnant, plan to become pregnant or are breast-feeding. If you become pregnant while taking levothyroxine, call your doctor.

If you have surgery, including dental surgery, tell the doctor or dentist that you are taking levothyroxine.

Is it safe during pregnancy or breastfeeding?

There are no adequate studies in women for determining risk when using levothyroxine during pregnancy or while breastfeeding. Please always consult with your doctor to weigh the potential benefits and risks before taking levothyroxine. Levothyroxine is pregnancy risk category A, according to the US Food and Drug Administration (FDA).

FDA pregnancy risk category reference below:

  • A=No risk
  • B=No risk in some studies
  • C=There may be some risk
  • D=Positive evidence of risk
  • X=Contraindicated
  • N=Unknown

Side effects

What side effects can occur from levothyroxine?

Get emergency medical help if you have any of these signs of an allergic reaction to levothyroxine: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have a serious side effect such as:

  • Fast or irregular heart rate
  • Fever, hot flashes, sweating
  • Sleep problems (insomnia)
  • Changes in your menstrual periods
  • Vomiting
  • Diarrhea
  • Appetite changes
  • Weight changes

Common side effects include:

  • Leg cramps
  • Muscle weakness
  • Headache
  • Feeling nervous or irritable
  • Diarrhea
  • Skin rash
  • Mild hair loss

Not everyone experiences these side effects. There may be some side effects not listed above. If you have any concerns about a side-effect, please consult your doctor or pharmacist.


What drugs may interact with levothyroxine?

Levothyroxine may interact with other drugs that you are currently taking, which can change how your drug works or increase your risk for serious side effects. To avoid any potential drug interactions, you should keep a list of all the drugs you are using (including prescription drugs, nonprescription drugs, and herbal products) and share it with your doctor and pharmacist. For your safety, do not start, stop, or change the dosage of any drugs without your doctor’s approval.

Products that may interact with this drug are:

  • Calcium carbonate (Alka-Mints, Calcium Oyster Shell, Caltrate, Os-Cal, Oyster Shell Calcium, Rolaids Soft Chew, Tums, and others)
  • Cholestyramine, colestipol
  • Ferrous sulfate iron supplement
  • Sucralfate
  • Sodium polystyrene sulfonate (Kalexate, Kayexalate, Kionex)
  • Antacids that contain aluminum or magnesium – Acid Gone, Gaviscon, Maalox, Milk of Magnesia, Mintox, Mylanta, Pepcid Complete, and others)

Does food or alcohol interact with levothyroxine?

Levothyroxine may interact with food or alcohol by altering the way the drug works or increase the risk for serious side effects. Please discuss with your doctor or pharmacist any potential food or alcohol interactions before using this drug.

What health conditions may interact with levothyroxine?

Levothyroxine may interact with your health condition. This interaction may worsen your health condition or alter the way the drug works. It is important to always let your doctor and pharmacist know all the health conditions you currently have.

Health conditions that may interact with this drug are:

  • Adrenal gland insufficiency (underactive adrenal gland)
  • Heart attack, acute or recent
  • Thyrotoxicosis (overactive thyroid)
  • Adrenal problems
  • Anemia, pernicious
  • Angina (severe chest pain)
  • Blood clotting problems
  • Diabetes
  • Heart or blood vessel disease (e.g., coronary artery disease)
  • Heart rhythm problems (e.g., arrhythmia, atrial fibrillation)
  • Osteoporosis
  • Pituitary gland problems
  • Patients who have trouble swallowing capsules


The information provided is not a substitute for any medical advice. You should ALWAYS consult with your doctor or pharmacist before using levothyroxine.

What is the dose of levothyroxine for an adult?

Usual Adult Dose for Hypothyroidism – Oral

The initial dose is 12.5 to 50 mcg orally once a day. The dosage can be increased in 12.5 to 25 mcg/day increments every 2 to 4 weeks.

In older patients or in younger patients with a history of cardiovascular disease, the dosage should be increased in 12.5 to 25 mcg increments every 3 to 6 weeks.

Usual Adult Dose for TSH Suppression – Oral:

The initial dose is 50 mcg orally once a day. The dosage may be increased in 25 to 50 mcg increments every 2 to 4 weeks. The typical maintenance dose is 100 to 200 mcg orally once a day.

Usual Adult Dose for Thyroid Suppression Test – Oral:

2.6 mcg/kg/day for 7 to 10 days.

Usual Adult Dose for Myxedema Coma:

Initial dose: 300 to 500 mcg IV bolus administered one time.

What is the dose of levothyroxine for a child?

Usual Pediatric Dose for Hypothyroidism

Congenital hypothyroidism:


  • Oral: 10 to 15 mcg/kg/day; if patient is at risk for development of cardiac failure, begin with a lower dose. In severe cases of hypothyroidism (T4 less than 5 mcg/dL), a higher initial dose of 12 to 17 mcg/kg/day may be considered.
  • IV or IM: 50% to 75% of the oral dose.

0 to 3 months:

  • 10 to 15 mcg/kg orally once per day; if the infant is at risk for development of cardiac failure use a lower starting dose of approximately 25 mcg/day; if the initial serum T4 is very low (less than 5 mcg/dL) begin treatment at a higher dosage of approximately 50 mcg/day.

3 to 6 months:

  • 8 to 10 mcg/kg or 25 to 50 mcg orally once per day.

6 to 12 months:

  • 6 to 8 mcg/kg or 50 to 75 mcg orally once per day.

1 to 5 years:

  • 5 to 6 mcg/kg or 75 to 100 mcg orally once per day.

6 to 12 years:

  • 4 to 5 mcg/kg or 100 to 125 mcg orally once per day.

12 years:

  • 2 to 3 mcg/kg or greater than or equal to 150 mcg orally once per day.

Patients in which growth and puberty are complete: 1.7 mcg/kg orally once per day.

For chronic or severe hypothyroidism: 25 mcg orally once per day and increase dosage as needed in increments of 25 mcg every 2 to 4 weeks until the desired effect is achieved.

How is levothyroxine available?

Levothyroxine is available in the following dosage forms and strengths:

  • Injection
  • Tablet

What should I do in case of an emergency or overdose?

In case of an emergency or an overdose, call your local emergency services or go to your nearest emergency room.

What should I do if I miss a dose?

If you miss a dose of levothyroxine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and take your regular dose as scheduled. Do not take a double dose.

Hello Health Group does not provide medical advice, diagnosis or treatment.


Levothyroxine. https://www.drugs.com/levothyroxine.html. Accessed July 25, 2017

Levothyroxine. http://www.mims.com/philippines/drug/info/levothyroxine%20sodium?mtype=generic. Accessed July 25, 2017

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Written by Stephanie Nicole Nera, RPh, PharmD on May 02, 2020
Medically reviewed by Stephanie Nicole Nera, RPh, PharmD