This medicine is a thyroid hormone used to treat hypothyroidism. It may also be used to treat other conditions as determined by your doctor.

Levothyroxine is the generic name for Synthroid.

What is the most important information I should know about levothyroxine?

- It is important to take levothyroxine regularly to get the most benefit.

- Do not stop taking this medication without talking to your doctor. It is important to take this medication to replace the thyroid hormone that the body is not producing. Even if you feel well, you may still need to take this medicine every day.

- Do not change brands or change to a generic levothyroxine drug product without first talking to your doctor. Some levothyroxine products may not be interchangeable.

What is levothyroxine?

- Levothyroxine is a naturally occurring hormone produced by the thyroid. It is important for normal energy and metabolism. For a variety of reasons, the body may not produce enough of this hormone on its own. In these cases, levothyroxine is taken to replace the body's natural thyroid hormone.

- Levothyroxine is used to treat hypothyroidism (low thyroid function). Levothyroxine is also used to prevent and treat goiter (growth or enlargement of the thyroid gland). Causes of goiter include hormonal imbalances, radiation, surgery, and cancer.

- Levothyroxine may also be used for purposes other than those listed in this medication guide.

What should I discuss with my healthcare provider before taking levothyroxine?

- Since thyroid hormone occurs naturally in the body, almost anyone can take this drug. In general, levothyroxine should not be taken if you have other hormonal problems that are not being adequately treated.

- Before taking this medication, tell your doctor if you have a heart disease such as coronary artery disease, hypertension, or angina. These conditions may be affected by thyroid therapy, and closer monitoring may be necessary at the start of therapy.

- Changes in blood sugar may occur if you have diabetes, and special monitoring may be necessary.

- Levothyroxine is in the FDA pregnancy category A. This means that levothyroxine is safe for use during pregnancy. It is also safe to take thyroid hormones if you are breast-feeding a baby. This drug does pass into breast milk, but it is not expected to be harmful to a nursing infant.

How should I take levothyroxine?

- Take this medication exactly as directed by your doctor. If you do not understand these directions, ask your doctor, nurse, or pharmacist to explain them to you.

- Take each dose with a full glass (8 ounces) of water.

- Take this medication at the same time each day whenever possible. Thyroid hormone is usually taken in the morning to prevent insomnia at night. Follow your doctor's instructions.

- It is important to take levothyroxine regularly to get the most benefit.

- Do not stop taking this medication without talking to your doctor. It is important to take this medication to replace the thyroid hormone that the body is not producing. Even if you feel well, you may still need to take this medicine every day.

- Do not change brands or change to a generic levothyroxine drug product without first talking to your doctor. Some levothyroxine products may not be interchangeable.

- Your doctor may want you to have blood tests or other medical evaluations during treatment with levothyroxine to monitor progress and side effects.

- Store levothyroxine at room temperature away from moisture and heat.

What happens if I miss a dose?

- Take the missed dose as soon as you remember. However, if it is almost time for the next dose, skip the missed dose and take only the next regularly scheduled dose. Do not take a double dose of this medication.

What happens if I overdose?

- Seek emergency medical treatment if an overdose is suspected.

- Symptoms of a levothyroxine overdose may include chest pain, nervousness, trouble sleeping, tremor, rapid heartbeat, nausea, headache, fever, sweating, shortness of breath, heat intolerance, irregular menses, increased appetite, decreased weight, diarrhea, and abdominal pain.

What should I avoid while taking levothyroxine?

- Do not change brands or change to a generic levothyroxine drug product without first talking to your doctor. Some levothyroxine products may not be interchangeable.

What are the possible side effects of levothyroxine?

- If you experience any of the following serious side effects, stop taking levothyroxine and seek emergency medical attention or contact your doctor immediately:

- an allergic reaction (difficulty breathing; closing of the throat; swelling of the lips, tongue, or face; or hives);
- vomiting; or
- chest pain, irregular heartbeat, shortness of breath.

- Other, less serious side effects may be more likely to occur. Continue to take levothyroxine and talk to your doctor or try another similar medication if you experience:

- tremor, nervousness, or irritability;
- headache;
- insomnia;
- diarrhea, changes in appetite, or weight loss;
- leg cramps;
- menstrual irregularities; or
- fever, sweating, or heat sensitivity.

- Side effects other than those listed here may also occur. Talk to your doctor about any side effect that seems unusual or that is especially bothersome.

What other drugs will affect levothyroxine?

- Other drugs may bind to levothyroxine and reduce the amount that is available in the body, making it less effective. Separate levothyroxine doses from the following medicines:

- antacids that contain aluminum;
- the prescription ulcer medicine sucralfate (Carafate);
- the cholesterol-lowering drugs cholestyramine (Questran) and colestipol (Colestid); and
- ferrous sulfate (a type of iron supplement).

- Drugs other than those listed here may also interact with levothyroxine or affect your condition. Talk to your doctor and pharmacist before taking any prescription or over-the-counter medicines, including vitamins, minerals, and herbal products.

Where can I get more information?

Your pharmacist has additional information about levothyroxine written for health professionals that you may read.