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Levothyroxine (By mouth)

Levothyroxine (lee-voe-thye-ROX-een)

Treats hypothyroidism. Also treats an enlarged thyroid gland and thyroid cancer.

Brand Name(s):

Levoxyl, Synthroid, Tirosint, Unithroid

There may be other brand names for this medicine.

When This Medicine Should Not Be Used:

This medicine is not right for everyone. Do not use it if you had an allergic reaction to glycerol, or you recently had a heart attack.

How to Use This Medicine:

Capsule, Liquid, Tablet

  • Take your medicine as directed. Your dose may need to be changed several times to find what works best for you. You may have to take this medicine for 6 to 8 weeks before your symptoms start to get better.
  • Read and follow the patient instructions that come with this medicine. Talk to your doctor or pharmacist if you have any questions.
  • Take this medicine in the morning on an empty stomach. Wait at least 30 to 60 minutes before you eat any food.
  • Capsule: Swallow whole. Do not cut or crush it.
  • Oral liquid:
    • This medicine may be mixed with water or be given directly into the mouth.
    • If mixed with water: Squeeze the contents of 1 single unit-dose ampule into a glass or cup containing water. Stir and drink it immediately. Add some water to the glass or cup and drink the water. This will help get all of the medicine out of the glass or cup. Do not mix this medicine with any other liquid except water. Do not store the mixture for later use.
    • If taken without water: Squeeze the medicine directly into the mouth or into a spoon and swallow it immediately.
  • Tablet: If this medicine is being given to a baby or a small child, you can crush the tablet and mix it in 1 to 2 teaspoons (5 to 10 milliliters) of water. This mixture can be given by spoon or dropper. Do not mix the tablet with any other liquid except water. Do not store the mixture. If you do not give the medicine right after it is mixed, throw it away.
  • Missed dose: Take a dose as soon as you remember. If it is almost time for your next dose, wait until then and take a regular dose. Do not take extra medicine to make up for a missed dose.
  • Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Use the oral liquid within 15 days after opening the pouch. Keep the ampules in the pouch until you are ready to use them.

Drugs and Foods to Avoid:

Ask your doctor or pharmacist before using any other medicine, including over-the-counter medicines, vitamins, and herbal products.

  • Some foods and medicines can affect how levothyroxine works. Tell your doctor if you are using any of the following:
    • Amiodarone, dexamethasone, digoxin, imatinib, ketamine, phenobarbital, rifampin
    • Beta-blocker medicine
    • Blood thinner (including heparin, warfarin)
    • Insulin or diabetes medicine
    • Medicine to treat depression
  • If you use antacids, medicine to treat high cholesterol (including cholestyramine, colesevelam, colestipol), orlistat, sevelamer, sucralfate, stomach medicine (including lansoprazole, omeprazole, pantoprazole), or any medicine that contains calcium or iron, take it at least 4 hours before or 4 hours after you take levothyroxine.
  • Cottonseed meal, dietary fiber, soybean flour (infant formula), or walnuts may decrease the absorption of this medicine. Talk with your doctor if you have questions.
  • Do not eat grapefruit or drink grapefruit juice while you are using this medicine.

Warnings While Using This Medicine:

  • Tell your doctor if you are pregnant or breastfeeding, or if you have anemia, blood clotting problems, diabetes, heart disease, osteoporosis, pituitary gland problems, or adrenal gland problems. Tell your doctor if you have recently received radiation therapy with iodine. Do not use this medicine to treat obesity or to lose weight.
  • Tell any doctor or dentist who treats you that you take this medicine.
  • Do not stop using this medicine suddenly. Your doctor will need to slowly decrease your dose before you stop it completely.
  • Your doctor will do lab tests at regular visits to check on the effects of this medicine. Keep all appointments.
  • Keep all medicine out of the reach of children. Never share your medicine with anyone.

Possible Side Effects While Using This Medicine:

Call your doctor right away if you notice any of these side effects:

  • Allergic reaction: Itching or hives, swelling in your face or hands, swelling or tingling in your mouth or throat, chest tightness, trouble breathing
  • Chest pain that may spread, trouble breathing, unusual sweating, fainting
  • Fast, pounding, or uneven heartbeat
  • Seizures or tremors
  • Severe headache, blurred or double vision, nausea, vomiting (in children)
  • Walking with a limp, knee or hip pain (in children)

If you notice these less serious side effects, talk with your doctor:

  • Appetite or weight changes
  • Changes in your menstrual periods
  • Hair loss
  • Nervousness, sensitivity to heat, sweating

If you notice other side effects that you think are caused by this medicine, tell your doctor

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088


Last Updated: 6/16/2017
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