Levothyroxine is used to treat hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormone. Levothyroxine is also used to help decrease the size of enlarged thyroid glands (also called a goiter) and to treat thyroid cancer.

This medicine is available only with your doctor's prescription.

This medicine will need to be taken for the rest of your life or your child's life. Do not stop taking this medicine or change your dose without first checking with your doctor. It may take several weeks before you start to notice that your symptoms are better.

It is best to take this medicine on an empty stomach. Take it with a full glass of water at least 30 minutes to 1 hour before eating breakfast.

Swallow the capsule whole. Do not cut or crush it. Also, if you are taking multiple strengths of this medicine, remove the capsules from the blisters in advance to help you identify the strength of each capsule.

For infants and children who cannot swallow the tablet form, the tablet can be crushed and mixed with a small amount of water (5 to 10 milliliters [mL] or 1 to 2 teaspoonfuls). You may use a spoon or dropper to give the mixture. Use the mixture right away and do not store it to use later.

If you are using the oral liquid:

This medicine should come with patient instructions. Read and follow the instructions carefully. Ask your doctor if you have any questions.
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.
This medicine should be taken at least 4 hours before or 4 hours after these medicines: antacids (Maalox®, Mylanta®, Tums®), calcium supplements, stomach medicines (including lansoprazole, omeprazole, pantoprazole, Aciphex®, Dexilant®, Nexium®, Prevacid®, Prilosec®), cholestyramine (Prevalite®, Questran®), colesevelam (Welchol®), colestipol (Colestid®), iron supplements, Kayexalate®, orlistat (Alli®, Xenical®), simethicone (Gas-X®, Mylicon®), and sucralfate (Carafate®).

Cotton seed meal, dietary fiber, soybean flour (infant formula), or walnuts may affect the absorption of this medicine from your body. You may have to take this medicine at a different time of day from when you eat these foods. Talk with your doctor more about this if you have concerns.

Do not eat grapefruit or drink grapefruit juice while you are using this medicine.

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur:

Less common

Chest pain or discomfort

decreased urine output

difficult or labored breathing

difficulty with swallowing

dilated neck veins

extreme fatigue

fainting

fast, slow, irregular, pounding, or racing heartbeat or pulse

fever

heat intolerance

hives or welts, skin itching, rash, or redness

irregular breathing

irritability

menstrual changes

nausea

pain or discomfort in the arms, jaw, back, or neck

sweating

swelling of the eyes, face, lips, throat, or tongue

tightness in the chest

tremors

Rare

Blurred or double vision

dizziness

eye pain

lack or slowing of normal growth in children

limp or walk favoring one leg

pain in the hip or knee

seizures

severe headache

Get emergency help immediately if any of the following symptoms of overdose occur:

Symptoms of overdose

Change in consciousness

cold, clammy skin

confusion

disorientation

fast or weak pulse

lightheadedness

loss of consciousness

sudden headache

sudden loss of coordination

sudden slurring of speech

Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Less common

Abdominal or stomach cramps

change in appetite

crying

diarrhea

false or unusual sense of well-being

fear or nervousness

feeling not well or unhappy

feeling of discomfort

feeling of warmth

feeling things are not real

feelings of suspicion and distrust

hair loss

headache

increased appetite

mental depression

muscle weakness

quick to react or overreact emotionally

rapidly changing moods

redness of the face, neck, arms, and occasionally, upper chest

restlessness

trouble getting pregnant

trouble sitting still

unusual tiredness or weakness

vomiting

weight gain or loss

Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

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

If you will be taking this medicine for a long time, it is very important that your doctor check the progress of you or your child at regular visits. This will allow your doctor to see if the medicine is working properly and to decide if you should continue to take it. Blood tests will be needed to check for unwanted effects.

Levothyroxine should not be used for the treatment of obesity or for the purpose of losing weight. This medicine is not effective for weight reduction. If taken in large amounts, levothyroxine may cause serious unwanted effects.

Hypothyroidism can sometimes cause infertility in men and women. Levothyroxine should not be used for the treatment of infertility unless it is caused by hypothyroidism.

For patients with diabetes: It is very important that you keep track of your blood or urine sugar levels as instructed by your doctor. Check with your doctor right away if you notice any changes in your sugar levels.

If you think you have become pregnant while using this medicine, tell your doctor right away. You may need a larger dose of levothyroxine while you are pregnant.

Women who are post-menopausal or who use this medicine for a long time may have some bone loss, which could lead to osteoporosis. Talk with your doctor if you have questions or concerns about this.

Call your doctor right away if you or your child start to have rapid or irregular heartbeats, chest pain, leg cramps, headaches, nervousness, irritability, sleeplessness, tremors, a change in appetite, weight gain or loss, vomiting, diarrhea, excessive sweating, heat intolerance, a fever, changes in menstrual periods, hives, or a skin rash. These could be symptoms of too much medicine in your body.

Do not suddenly stop taking this medicine without first checking with your doctor. Your doctor may want you or your child to gradually reduce the amount you are using before stopping completely.

Make sure any doctor or dentist who treats you knows that you or your child are using this medicine. You or your child may need to stop using this medicine several days before having surgery or medical tests.

A temporary loss of hair may occur during the first few months of levothyroxine therapy. Ask your doctor about this if you have any concerns.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.