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

When This Medicine Should Not Be Used

How to Use This Medicine

Capsule, 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.
  • 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.
  • 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.

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 medicines and foods can affect how levothyroxine works. Make sure your doctor knows if you use digoxin, a blood thinner (such as heparin, warfarin), insulin or diabetes medicine that you take by mouth (such as glimepiride, glipizide, glyburide, metformin, repaglinide, tolbutamide), or medicine to treat depression (such as amitriptyline, doxepin, imipramine, maprotiline, nortriptyline, sertraline).
  • If you use antacids, medicine to treat high cholesterol (such as cholestyramine, colesevelam, colestipol), orlistat, sevelamer, sucralfate, 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.

Warnings While Using This Medicine

  • Tell your doctor if you are pregnant or breastfeeding, or if you have blood clotting problems, diabetes, heart or blood vessel disease (such as coronary artery disease), heart rhythm problems, angina, osteoporosis, pernicious anemia, pituitary gland problems, or adrenal gland problems.
  • This medicine could cause bone loss, which could lead to osteoporosis. Talk with your doctor if you have questions or concerns about this.
  • If you have diabetes, monitor your blood or urine sugar levels as directed by your doctor. Tell your doctor right away if you notice any changes in your sugar levels.
  • 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
  • Fast, pounding, or uneven heartbeat
  • Chest pain that may spread, trouble breathing, nausea, unusual sweating, fainting
  • Seizure 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

Version Info

  • Last reviewed on 12/12/2016

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