Levothyroxine

Pronunciation

Generic Name: levothyroxine (LEE-voe-thye-ROX-een)
Brand Name: Examples include Levoxyl and Synthroid

Do not use levothyroxine alone or with other medicines to treat obesity or to lose weight. Incorrect use of levothyroxine may cause serious and sometimes fatal side effects.


Levothyroxine is used for:

Treating low thyroid hormone levels and certain types of goiters. It is also used with surgery and other medicines for managing certain types of thyroid cancer. It may also be used for other conditions as determined by your doctor.

Levothyroxine is a thyroid hormone. It works by replacing thyroid hormone when your body does not make enough on its own.

Do NOT use levothyroxine if:

  • you are allergic to any ingredient in levothyroxine
  • you have untreated adrenal gland problems or high thyroid hormone levels
  • you have had a recent heart attack

Contact your doctor or health care provider right away if any of these apply to you.

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Before using levothyroxine:

Some medical conditions may interact with levothyroxine. Tell your doctor or pharmacist if you have any medical conditions, especially if any of the following apply to you:

  • if you are pregnant, planning to become pregnant, or are breast-feeding
  • if you are taking any prescription or nonprescription medicine, herbal preparation, or dietary supplement
  • if you have allergies to medicines, foods, or other substances
  • if you have trouble swallowing, heart or blood vessel problems (eg, coronary artery disease), high blood pressure, blood clotting or bleeding problems, pernicious anemia, diabetes, bone problems (eg, osteoporosis), fertility problems, pituitary problems, adrenal gland problems, or other thyroid problems
  • if you have problems absorbing nutrition from your stomach or intestines into your body
  • if you had a recent surgery or have an upcoming surgery

Some MEDICINES MAY INTERACT with levothyroxine. Tell your health care provider if you are taking any other medicines, especially any of the following:

  • Many prescription and nonprescription medicines (eg, used for infections, inflammation, aches and pains, nasal congestion, asthma, high blood pressure, irregular heartbeat or other heart problems, blood thinning, mental or mood problems, depression, diabetes, other thyroid problems, high cholesterol, hepatitis, weight loss, heartburn, birth control, hormone replacement therapy, growth hormone deficiency, cancer, seizures), and multivitamin products may interact with levothyroxine, increasing the risk of side effects or decreasing effectiveness.

This may not be a complete list of all interactions that may occur. Ask your health care provider if levothyroxine may interact with other medicines that you take. Check with your health care provider before you start, stop, or change the dose of any medicine.

How to use levothyroxine:

Use levothyroxine as directed by your doctor. Check the label on the medicine for exact dosing instructions.

  • Take levothyroxine by mouth on an empty stomach at least one-half to one hour before breakfast.
  • Some brands of levothyroxine must be taken with a full glass of water (8 oz/240 mL). Ask your pharmacist how you should take your brand of levothyroxine.
  • Do not take an antacid or a product that has iron or calcium in it within 4 hours of taking levothyroxine.
  • If the patient is a child or if you cannot swallow the tablet whole, you may crush the correct dose of the medicine. Add the crushed medicine to 1 to 2 teaspoons (5 to 10 mL) of water. Mix well. Use a spoon or dropper to give the medicine as soon as possible. Do not store the mixture for later use. Do not mix crushed tablets in soybean infant formula. Ask your pharmacist if you have any questions.
  • Levothyroxine works best if it is taken at the same time each day.
  • Continue to take levothyroxine even if you feel well. Do not miss any doses.
  • It may take several weeks before you notice an improvement in your symptoms. Do not stop or change your dose of levothyroxine without first checking with your doctor.
  • If you miss a dose of levothyroxine, take it as soon as possible. If it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not take 2 doses at once.

Ask your health care provider any questions you may have about how to use levothyroxine.

Important safety information:

  • Some brands of levothyroxine may cause choking, gagging, or trouble swallowing. Ask your pharmacist if your brand may cause these effects. If your brand may cause these effects, be sure to take your medicine with a full glass of water. Tell your doctor if you have trouble swallowing.
  • It is important to take levothyroxine exactly as prescribed. Do not take more than the prescribed dose without checking with your doctor.
  • Tell your doctor or dentist that you take levothyroxine before you receive any medical or dental care, emergency care, or surgery.
  • Diabetes patients - Levothyroxine may affect your blood sugar. Check blood sugar levels closely. Ask your doctor before you change the dose of your diabetes medicine.
  • Foods that contain soybean flour (including infant formula), cottonseed meal, walnuts, or dietary fiber may decrease the absorption of levothyroxine. Tell your doctor if your diet includes any of these foods. Your doctor may need to change your dose of levothyroxine.
  • Mild hair loss may rarely occur during the first few months of treatment with levothyroxine. This is usually temporary. Contact your doctor if hair loss is severe or persistent.
  • Lab tests, including thyroid hormone level and growth checks, may be performed while you use levothyroxine. These tests may be used to monitor your condition or check for side effects. Be sure to keep all doctor and lab appointments.
  • Use levothyroxine with caution in the ELDERLY; they may be more sensitive to its effects, especially heart problems.
  • CHILDREN and teenagers may need regular growth checks while they take levothyroxine.
  • PREGNANCY and BREAST-FEEDING: If you become pregnant, contact your doctor. Your doctor may need to change your dose of levothyroxine. Levothyroxine is found in breast milk. If you are or will be breast-feeding while you use levothyroxine, check with your doctor. Discuss any possible risks to your baby.

Possible side effects of levothyroxine:

All medicines may cause side effects, but many people have no, or minor, side effects. No COMMON side effects have been reported with the use of levothyroxine. Seek medical attention right away if any of these SEVERE side effects occur:

Severe allergic reactions (rash; hives; itching; difficulty breathing; flushing; tightness in the chest; swelling of the mouth, face, lips, or tongue; unusual hoarseness); changes in appetite; changes in menstrual periods; chest pain; diarrhea; excessive sweating; fast or irregular heartbeat; fever; heat intolerance; joint pain; leg cramps; mental or mood changes (eg, anxiety, irritability, nervousness); muscle weakness; seizures; severe or persistent headache or fatigue; shortness of breath; stomach cramps; tremors; trouble sleeping; unusual weight gain or weight loss; vomiting; wheezing.

This is not a complete list of all side effects that may occur. If you have questions about side effects, contact your health care provider. Call your doctor for medical advice about side effects. To report side effects to the appropriate agency, please read the Guide to Reporting Problems to FDA.

If OVERDOSE is suspected:

Contact 1-800-222-1222 (the American Association of Poison Control Centers), your local poison control center, or emergency room immediately. Symptoms may include coma; confusion; disorientation; seizures.

Proper storage of levothyroxine:

Store levothyroxine between 68 and 77 degrees F (20 and 25 degrees C). Brief storage at temperatures between 59 and 86 degrees F (15 and 30 degrees C) is permitted. Protect from heat, light, and moisture. Do not store in the bathroom. Keep levothyroxine out of the reach of children and away from pets.

General information:

  • If you have any questions about levothyroxine, please talk with your doctor, pharmacist, or other health care provider.
  • Levothyroxine is to be used only by the patient for whom it is prescribed. Do not share it with other people.
  • If your symptoms do not improve or if they become worse, check with your doctor.
  • Check with your pharmacist about how to dispose of unused medicine.

This information should not be used to decide whether or not to take levothyroxine or any other medicine. Only your health care provider has the knowledge and training to decide which medicines are right for you. This information does not endorse any medicine as safe, effective, or approved for treating any patient or health condition. This is only a brief summary of general information about levothyroxine. It does NOT include all information about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to levothyroxine. This information is not specific medical advice and does not replace information you receive from your health care provider. You must talk with your healthcare provider for complete information about the risks and benefits of using levothyroxine.

Issue Date: July 2, 2014
Database Edition 14.3.1.001
Copyright © 2014 Wolters Kluwer Health, Inc.

Disclaimer: This information should not be used to decide whether or not to take this medicine or any other medicine. Only your health care provider has the knowledge and training to decide which medicines are right for you. This information does not endorse any medicine as safe, effective, or approved for treating any patient or health condition. This is only a brief summary of general information about this medicine. It does NOT include all information about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to this medicine. This information is not specific medical advice and does not replace information you receive from your health care provider. You must talk with your healthcare provider for complete information about the risks and benefits of using this medicine.

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