Levothyroxine, a thyroid hormone, is used to treat hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormone. Without this hormone, the body cannot function properly, resulting in poor growth, slow speech, lack of energy, weight gain, hair loss, dry thick skin, and increased sensitivity to cold. When taken correctly, levothyroxine reverses these symptoms. Levothyroxine is also used to treat congenital hypothyroidism (cretinism) and goiter (enlarged thyroid gland).

How should this medicine be used?

Levothyroxine comes as a tablet to take by mouth. It usually is taken as a single dose before breakfast every day. To control the symptoms of hypothyroidism, you probably will need to take this medicine for the rest of your life. It may take about 2 weeks before you notice any change in your symptoms. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take levothyroxine exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

Continue to take levothyroxine even if you feel well. Do not stop taking levothyroxine without talking to your doctor.

What special precautions should I follow?

Before taking levothyroxine,

• tell your doctor and pharmacist if you are allergic to levothyroxine, thyroid hormone, any other drugs, povidone iodine, tartrazine (a yellow dye in some processed foods and drugs), or foods such as lactose or corn starch. Levothroid and Eltroxin contain lactose, while Synthroid contains tartrazine and povidone. Eltroxin contains corn starch.
• tell your doctor and pharmacist what prescription and nonprescription medications you are taking, especially amphetamines; antacids; anticoagulants ('blood thinners') such as warfarin (Coumadin); antidepressants or anti-anxiety agents; arthritis medicine; aspirin; beta-blockers such as metoprolol (Lopressor, Toprol), propranolol (Inderal) or timolol (Blocadren, Timoptic); cancer chemotherapy agents; cholesterol-lowering resins such as cholestyramine (Questran) or colestipol (Colestid); diabetes medications (insulin and tablets); digoxin (Lanoxin); estrogens; iron; methadone; oral contraceptives; phenytoin (Dilantin); sodium polystrene sulfonate (Kayexalate); sucralfate (Carafate); steroids; theophylline (TheoDur); and vitamins.
• if you take cholestyramine (Questran) or colestipol (Colestid), take it at least 4 hours before or 1 hour after taking levothyroxine.
• tell your doctor if you have or have ever had diabetes; hardening of the arteries (atherosclerosis); kidney disease; hepatitis; cardiovascular disease such as high blood pressure, chest pain (angina), arrhythmias, or heart attack; or an underactive adrenal or pituitary gland.
• tell your doctor if you are pregnant, plan to become pregnant or are breast-feeding. If you become pregnant while taking levothyroxine, call your doctor.
• if you have surgery, including dental surgery, tell the doctor or dentist that you are taking levothyroxine.

What special dietary instructions should I follow?

Levothyroxine may cause an upset stomach. Take levothyroxine with food or milk.

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 side effects can this medication cause?

Although side effects from levothyroxine are not common, they can occur. Tell your doctor if any of these symptoms are severe or do not go away:

• weight loss
• tremor
• headache
• upset stomach
• vomiting
• diarrhea
• stomach cramps
• nervousness
• irritability
• insomnia
• excessive sweating
• increased appetite
• fever
• changes in menstrual cycle
• sensitivity to heat
• temporary hair loss, particularly in children during the first month of therapy

If you experience either of the following symptoms, call your doctor immediately:

• chest pain (angina)
• rapid or irregular heartbeat or pulse

What storage conditions are needed for this medicine?

Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom). Throw away any medication that is outdated or no longer needed. Talk to your pharmacist about the proper disposal of your medication.

In case of emergency/overdose

In case of overdose, call your local poison control center at 1-800-222-1222. If the victim has collapsed or is not breathing, call local emergency services at 911.

What other information should I know?

Keep all appointments with your doctor and the laboratory. Your doctor will order certain lab tests to check your response to levothyroxine.

Learn the brand name and generic name of your medication. Do not switch brands without talking to your doctor or pharmacist, as each brand of levothyroxine contains a slightly different amount of medication.

Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.