Synthroid (Levothyroxine; a thyroid hormone), is used to treat hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormone. Levothyroxine is also used to treat congenital hypothyroidism (cretinism) and goiter (enlarged thyroid gland). Levothyroxine is also used with surgery and radioactive iodine therapy to treat thyroid cancer. Levothyroxine is in a class of medications called hormones. It works by replacing the thyroid hormone that is normally produced by the body. Without thyroid hormone, your body cannot function properly, which may result in poor growth, slow speech, lack of energy, excessive tiredness, constipation, weight gain, hair loss, dry, thick skin, increased sensitivity to cold, joint and muscle pain, heavy or irregular menstrual periods, and depression. When taken correctly, levothyroxine reverses these symptoms

Levothyroxine comes as a tablet and a capsule to take by mouth. It usually is taken once a day on an empty stomach, one half to one hour before breakfast. 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. Swallow capsules whole; do not chew or crush them. The tablets may get stuck in your throat or cause choking or gagging; therefore, the tablet should be taken with a full glass of water. If you are giving levothyroxine to an infant, child, or adult who cannot swallow the tablet, crush the tablet and mix it in 1 to 2 teaspoons of plain water. Give this mixture by spoon or dropper right away. Do not store this mixture. Only mix the crushed tablets with water. Do not mix with food or soybean infant formula. Your doctor will probably start you on a low dose of levothyroxine and gradually increase your dose. Levothyroxine controls hypothyroidism, but does not cure it. It may take several weeks before you notice a change in your symptoms. Continue to take levothyroxine even if you feel well. Do not stop taking levothyroxine without talking to your doctor.

Before taking levothyroxine,

• tell your doctor and pharmacist if you are allergic to levothyroxine, thyroid hormone, any other medications, or any of the ingredients in levothyroxine. Ask your pharmacist for a list of the ingredients.
• tell your doctor and pharmacist what prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention any of the following: amiodarone (Cordarone, Pacerone); amphetamines; anticoagulants ('blood thinners') such as warfarin (Coumadin); aspirin or aspirin-containing products and other nonsteroidal anti-inflammatory drugs; beta-blockers such as metoprolol (Lopressor), corticosteroids such as dexamethasone; digoxin (Lanoxin); estrogens; furosemide (Lasix); imatinib (Gleevac); insulin or other medications to treat diabetes; lithium (Lithobid); maprotiline; oral contraceptives; phenobarbital; selective serotonin reuptake inhibitors (SSRIs) such as sertraline (Zoloft); theophylline (TheoDur); and tricyclic antidepressants such as amitriptyline (Elavil). Many other medications may also interact with levothyroxine, so be sure to tell your doctor about all the medications you are taking, even those that do not appear on this list. Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
• if you take an antacid, calcium carbonate (Tums), cholestyramine (Questran), colesevelam (Welchol), colestipol (Colestid), iron, orlistat (Alli, Xenical), simethicone (Phazyme, Gas X), sevelamer (Renvela, Renagel), sodium polystyrene sulfonate (Kayexalate), or sucralfate (Carafate), take it at least 4 hours before or 4 hours after you take levothyroxine.
• tell your doctor if you have or have ever had diabetes; hardening of the arteries (atherosclerosis); kidney disease; liver disease or hepatitis; bleeding problems; porphyria (condition in which abnormal substances build up in the blood and cause problems with the skin or nervous system); cardiovascular disease such as high blood pressure, chest pain (angina), arrhythmias, or heart attack; an underactive adrenal or pituitary gland, or any condition that makes it difficult for you to swallow.
• 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.

Levothyroxine may cause side effects including but not limited to:

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

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

If you experience either of the following symptoms, call your doctor immediately or get emergency medical treatment:

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

If your condition doesn’t improve or worsens, let your physician know immediately.    

Q: Why is Synthroid prescribed?

A: Synthroid is a thyroid medicine that replaces a hormone normally produced by your thyroid gland to regulate the body's energy and metabolism.

Q: Does Synthroid have a generic alternative?

A: Synthroid is only available in the brand name. 

Q: How long until I see the effects of Synthroid?

A: It may take several weeks before your body starts to respond to levothyroxine. Keep using this medicine even if you feel well.

Q: What if I miss a dose of Synthroid?

A: Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

Q: How should I store this medication?

A: 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).