Synthroid is used for:

Treating low thyroid activity and treating or suppressing different types of goiters. It is also used with surgery and other medicines for managing certain types of thyroid cancer.

Synthroid is a thyroid hormone. Thyroid hormones are produced and released by the thyroid gland and regulate the body's metabolism. When the thyroid gland is underactive (hypothyroidism) it does not produce enough thyroid hormone and metabolism slows.

Do NOT use Synthroid if:
you are allergic to any ingredient in Synthroid
you have a history of heart attack, chest pain (angina), adrenal gland problems, or elevated thyroid hormone levels that have not been treated

Contact your doctor or health care provider right away if any of these apply to you.

Before using Synthroid :

Some medical conditions may interact with Synthroid . Tell your doctor or pharmacist if you have any medical conditions, especially if any of the following apply to you:
if you are pregnant, planning to become pregnant, or are breast-feeding
if you are taking any prescription or nonprescription medicine, herbal preparation, or dietary supplement
if you have allergies to medicines, foods, or other substances
if you have heart problems, high blood pressure, blood clotting problems, diabetes, bone loss (osteoporosis), digestion or nutrient absorption problems, infertility problems, pituitary gland problems, high thyroid levels, or other thyroid problems
If you have just had or are scheduled for surgery

Some MEDICINES MAY INTERACT with Synthroid . Tell your health care provider if you are taking any other medicines, especially any of the following:
Aluminum salts (eg, antacids), aminoquinolones (eg, chloroquine), amiodarone, HMG-CoA reductase inhibitors (eg, simvastatin), iron salts (eg, ferrous sulfate), raloxifene, rifampin, sertraline, or sucralfate because they may decrease Synthroid 's effectiveness
HMG-CoA reductase inhibitors (eg, simvastatin) or tricyclic antidepressants (eg, amitriptyline) because side effects such as nervousness, fast heart rate, or irregular heartbeat may occur
Anticoagulants (eg, warfarin) or ketamine because their actions and the risk of their side effects may be increased by Synthroid
Beta-blockers (eg, metoprolol) or digitalis glycosides (eg, digoxin) because their effectiveness may be decreased by Synthroid

This may not be a complete list of all interactions that may occur. Ask your health care provider if Synthroid may interact with other medicines that you take. Check with your health care provider before you start, stop, or change the dose of any medicine.

How to use Synthroid :

Use Synthroid as directed by your doctor. Check the label on the medicine for exact dosing instructions.
Take Synthroid on an empty stomach at least 1 hour before or 2 to 3 hours after eating. It is recommended that you take your dose 1 hour before breakfast unless otherwise directed by your doctor.
Take Synthroid with a full glass of water (8 oz/240 mL).
Notify your health care provider if you eat foods that contain soybean flour (infant formula), cottonseed meal, walnuts, or dietary fiber. These foods decrease the absorption of Synthroid . Your doctor may need to change your dose of Synthroid .
Take Synthroid 4 hours apart from calcium supplements, iron, antacids (those containing aluminum, calcium, or magnesium), simethicone, cholestyramine, colestipol, sucralfate, or sodium polystyrene sulfonate. These medicines may decrease the absorption of Synthroid into your bloodstream.
Synthroid works best if it is taken at the same time each day.
It may take several weeks (4 to 6 weeks) before you notice an improvement in your symptoms.
Synthroid will usually have to be taken for life, except in the cases of temporary low thyroid activity associated with thyroid inflammation and in patients who are taking Synthroid on a trial basis.
For children or patients who cannot swallow whole tablets: Crush the tablet and mix in 1 or 2 teaspoons (5 or 10 mL) of water, and give using a spoon or dropper as soon as possible after preparation. Do not store the mixture for later use. Do not mix crushed tablets in soybean infant formula. Consult your pharmacist for more information.
If you miss a dose of Synthroid and you are taking it regularly, take it as soon as possible. If several hours have passed or if it is nearing time for the next dose, do not double the dose to catch up, unless advised by your health care provider. Do not take 2 doses at once.

Ask your health care provider any questions you may have about how to use Synthroid .

Important safety information:

Synthroid may rapidly swell and disintegrate resulting in choking, gagging, the tablet getting stuck in your throat, or difficulty swallowing. It is very important that you take the tablet with a full glass of water. Most of these problems disappeared when levothyroxine tablets were taken with water.
Tell your doctor or dentist that you take Synthroid before you receive any medical or dental care, emergency care, or surgery.
If you are taking blood thinners at the same time as Synthroid , lab tests will be required to adjust the blood thinners.
Diabetes patients - Synthroid may affect your blood sugar. Check blood sugar levels closely. Ask your doctor before you change the dose of your diabetes medicine.
Lab tests will be required to monitor therapy. Be sure to keep appointments.
Use Synthroid with caution in the ELDERLY; they may be more sensitive to its effects.
Synthroid should be used with caution in CHILDREN; overuse may reduce the child's final adult height.
PREGNANCY and BREAST-FEEDING: It is not known if Synthroid can cause harm to the fetus. If you become pregnant, contact your doctor. You will need to discuss the benefits and risks of using Synthroid while you are pregnant. Synthroid is found in breast milk. If you are or will be breast-feeding while you use Synthroid , check with your doctor. Discuss any possible risks to your baby.

Possible side effects of Synthroid :

All medicines may cause side effects, but many people have no, or minor, side effects. Check with your doctor if any of these most COMMON side effects persist or become bothersome:

Anxiety; diarrhea; flushing; mood swings; muscle weakness; partial, temporary hair loss; sleeplessness; stomach cramps; tiredness; vomiting.
Seek medical attention right away if any of these SEVERE side effects occur:

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); changes in appetite; changes in menstrual periods; chest pain; difficulty breathing; excessive sweating; fast heartbeat; fever; headache; hives or skin rash; hyperactivity; inability to handle warm or hot room/weather conditions; irregular heartbeat; irritability; leg cramps; nervousness; pounding in the chest; seizures; shortness of breath; tremors; weight gain or weight loss.