Synthroid (levothyroxine) is most commonly prescribed to treat hypothyroidism (low thyroid hormone). It can also be used to treat or prevent goiters (enlarged thyroid gland), which can be caused by hormone imbalances, radiation treatment, surgery, or cancer.

Synthroid assists in the regulation of the body's energy and metabolism by replacing the hormone normally produced by your thyroid gland. This medication is usually prescribed when your thyroid gland does not produce enough of this hormone on its own.

A doctor's prescription is required to buy Synthroid or its generic alternative, levothyroxine.

Always take Synthroid as directed by your physician. Do not stop taking this medicine or change your dose without consulting with your doctor.

It comes in both a tablet and capsule form to take by mouth. It usually is taken once a day on an empty stomach, 30 minutes to 1 hour before breakfast, unless otherwise directed by your physician. If you are giving levothyroxine to an infant, child, or adult who cannot swallow the tablet, you may be able to crush and mix it in 1 to 2 teaspoons (5 to 10 mL) of water. Only mix the crushed tablets with water; do not mix it with food or soybean infant formula. Administer this mixture by spoon or dropper right away. Do not store it for later use.

Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand.

Do not take more or less than your recommended Synthroid dose or take it more often than prescribed by your doctor.

If you will be taking this medicine for a long time, it is very important that your doctor routinely checks your progress during regular visits. Levothyroxine should not be used for the treatment of obesity or for the purpose of losing weight. 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, or are planning on becoming pregnant during the course of your treatment, tell your doctor right away. 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.

Do not suddenly stop taking this medicine without first checking with your doctor. Your doctor may want to gradually reduce the Synthroid dosage that you are using before stopping completely. Make sure any doctor or dentist who treats you knows that you are using this medicine. You 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, as drug interaction may occur. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.

Tell your doctor if any of these symptoms are severe or do not go away:

• weight gain or loss
• headache
• vomiting
• diarrhea
• changes in appetite
• fever
• changes in menstrual cycle
• sensitivity to heat
• hair loss
• joint pain
• leg cramps

Some side effects can be serious. If you experience either of the following symptoms or those listed in the IMPORTANT WARNING section, call your doctor immediately or get emergency medical treatment:

• Shortness of breath
• Wheezing
• Hives
• Itching
• Rash
• Flushing
• Stomach pain
• Nausea
• Swelling of hands, feet, ankles, or lower legs

What is this medicine?

Levothyroxine (lee voe thye ROX een) is a thyroid hormone. This medication can improve symptoms of thyroid deficiency such as slow speech, lack of energy, weight gain, hair loss, dry skin, and feeling cold. It can also help in the treatment of goiters (an enlarged thyroid gland).

What should I tell my health care provider before I take Synthroid?

Your doctor will need to know if you have any of these conditions before prescribing Synthroid:

• Addison's disease or other adrenal gland problem
• angina
• bone problems
• diabetes
• dieting or on a weight loss program
• fertility problems
• heart disease
• pituitary gland problem
• take medicines that treat or prevent blood clots
• an unusual or allergic reaction to levothyroxine, thyroid hormones, other medicines, foods, dyes, or preservatives
• pregnant or trying to get pregnant
• breast-feeding

What should I do if I forget a dose?

Take the missed dose as soon as you remember it. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.

What should I know about storage and disposal of this medication?

Keep all medications out of the reach of children.

Do not keep outdated medicine or medicine that is no longer needed.

Ask your healthcare professional how you should dispose of any medicine you do not use.

Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing

What special dietary instructions should I follow while on Synthroid?

Some foods and beverages, particularly those that contain soybeans, walnuts, and dietary fiber, may affect how levothyroxine works for you. Talk to your doctor before eating or drinking these foods.

Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medication.

What happens if I overdose on levothroxine?

Seek emergency medical attention if you think that you are experiencing a Synthroid overdose.

Overdose symptoms may include headache, leg cramps, tremors, feeling nervous or irritable, chest pain, shortness of breath, and fast or pounding heartbeats.

What interactions can you experience with Synthroid?

There are many possible drug interactions that you should be aware of. To avoid possible interactions, talk to your doctor before taking any other medications, vitamins, supplements, or making any large dietary changes.