Levothyroxine (By mouth)

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

Treats hypothyroidism, an enlarged thyroid gland, and thyroid cancer.

Brand Name(s):

Euthyrox, Levoxyl, Synthroid, Tirosint, Tirosint-Sol, 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 levothyroxine or glycerol, or if you have an uncorrected adrenal gland problem or a recent 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 4 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, at least 30 to 60 minutes before eating breakfast.
  • Capsule: Swallow whole. Do not cut, chew, 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 right away. 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 right away.
  • Tablet: If you are giving this medicine to a baby or child who cannot swallow the tablet whole, crush the tablet and mix it in 1 to 2 teaspoons (5 to 10 milliliters) of water. Give the mixture right away using a spoon or dropper. Do not mix the tablet with any other liquid except water. Do not store the mixture for future use.
  • 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, asparaginase, carbamazepine, clofibrate, dexamethasone, digoxin, 5-fluorouracil, furosemide, heroin, imatinib, ketamine, methadone, mitotane, nicotinic acid, phenobarbital, phenytoin, rifampin, tamoxifen
    • Beta-blocker medicine
    • Birth control pills (including estrogen)
    • Blood thinner (including heparin, warfarin)
    • Insulin or diabetes medicine
    • Medicine to treat depression (including amitriptyline, maprotiline)
    • NSAIDs
    • Salicylates
    • Steroids (including dexamethasone, androgens, anabolic steroids)
  • If you are using kayexalate, lanthanum, orlistat, sevelamer, sucralfate, antacids (including aluminum or magnesium hydroxide, simethicone), medicine to lower cholesterol (including cholestyramine, colesevelam, colestipol), stomach medicine (including lansoprazole, omeprazole, pantoprazole), or any medicine that contains calcium or iron, take them 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 kidney disease, liver disease, heart or blood vessel disease, anemia, blood clotting problems, diabetes, osteoporosis, pituitary gland problems, or adrenal gland problems. Tell your doctor if you have recently received radiation treatment with iodine.
  • This medicine may cause the following problems:
    • Heart problems, including angina (chest pain), heart rhythm problems
    • Myxedema coma, which may be life-threatening
    • Low bone density
  • This medicine should not be used to treat obesity or as part of a treatment plan for a weight control program.
  • Tell any doctor or dentist who treats you that you are taking 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
  • Confusion, swelling of the face, tongue, or lower legs, feeling cold, unusual tiredness or weakness
  • Dizziness, lightheadedness, stomach pain
  • 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
  • Diarrhea
  • Hair loss
  • Muscle spasm or weakness
  • Nervousness, sensitivity to heat
  • Trouble sleeping

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: 11/6/2020

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