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

Levothyroxine is used to treat hypothyroidism (low thyroid hormone). This medicine is given when your thyroid does not produce enough of this hormone on its own.

Levothyroxine is also used to treat or prevent goiter (enlarged thyroid gland), which can be caused by hormone imbalances, radiation treatment, surgery, or cancer.

You may not be able to take levothyroxine if you have certain medical conditions. Tell your doctor if you have an untreated or uncontrolled adrenal gland disorder, a thyroid disorder called thyrotoxicosis, or if you have any recent or current symptoms of a heart attack.

Levothyroxine should not be used to treat obesity or weight problems. Dangerous side effects or death can occur from the misuse of this medicine, especially if you are taking any other weight-loss medications or appetite suppressants.

Levothyroxine comes as a tablet and a capsule to take by mouth. It usually is taken once a day on an empty stomach, 30 minutes to 1 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. Do not remove the capsule from the package until you are ready to take it.

Take the tablets with a full glass of water as they may get stuck in your throat or cause choking or gagging.

If you are giving levothyroxine to an infant, child, or adult who cannot swallow the tablet, 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. Give this mixture by spoon or dropper right away. Do not store it for later use.

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.

Take levothyroxine exactly as it was prescribed for you. Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose.

Levothyroxine oral is taken by mouth. The injection is given as an infusion into a vein. Levothyroxine is usually given by injection only if you are unable to take the medicine by mouth.

Levothyroxine oral works best if you take it on an empty stomach, 30 to 60 minutes before breakfast. Follow your doctor's dosing instructions and try to take the medicine at the same time each day.

Swallow the tablet or capsule whole, with a full glass (8 ounces) of water. The tablet may dissolve very quickly and could swell in your throat.

Measure liquid medicine carefully. Use the dosing syringe provided, or use a medicine dose-measuring device (not a kitchen spoon).

Levothyroxine doses are based on weight in children. Your child's dose needs may change if the child gains or loses weight.

It may take several weeks before your body starts to respond to levothyroxine. Keep using this medicine even if you feel well. You may need to use this medicine for the rest of your life.

You may need frequent medical tests. Tell any doctor, dentist, or surgeon who treats you that you are using this medicine.

Store at room temperature away from moisture and heat. Use Tirosint-Sol and within 3 months after opening the pouch.

Do not share this medicine with another person, even if they have the same symptoms you have.

Levothyroxine should not be used to treat obesity or weight problems. Dangerous side effects or death can occur from the misuse of levothyroxine, especially if you are taking any other weight-loss medications or appetite suppressants.

Since thyroid hormone occurs naturally in the body, almost anyone can take levothyroxine. However, you may not be able to take this medicine if you have certain medical conditions.

To make sure levothyroxine is safe for you, tell your doctor if you have ever had:

• an untreated or uncontrolled adrenal gland disorder;

• a thyroid disorder called thyrotoxicosis; or

• symptoms of a heart attack (chest pain or heavy feeling, pain spreading to the jaw or shoulder, nausea, sweating, general ill feeling).

• a thyroid nodule;

• heart problems such as a heart attack, stroke, blood clot or blood clotting disorder;

• diabetes (your diabetes medicine may need to be adjusted);

• anemia (low red blood cells);

• weak bones (osteoporosis), or low bone mineral density;

• problems with your pituitary gland;

• any food or drug allergies;

• plan to have surgery;

• recently received radiation therapy with iodine (such as I-131); or

• kidney disease.

If you become pregnant while taking levothyroxine, do not stop taking the medicine without your doctor's advice. Having low thyroid hormone levels during pregnancy could harm both mother and baby. Your dose needs may be different during pregnancy.

Tell your doctor if you are breastfeeding. Your dose needs may be different while you are nursing.

Do not give this medicine to a child without medical advice. Tirosint is not approved for use by anyone younger than 6 years old.

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.

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

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

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).

It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location – one that is up and away and out of their sight and reach. http://www.upandaway.org

Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA's Safe Disposal of Medicines website (http://goo.gl/c4Rm4p) for more information if you do not have access to a take-back program.

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.

Avoid the following food products, which can make your body absorb less levothyroxine: grapefruit juice, infant soy formula, soybean flour, cotton seed meal, walnuts, and high-fiber foods.

Get emergency medical help if you have signs of an allergic reaction to levothyroxine: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Levothyroxine may cause serious side effects. Call your doctor at once if you have:

• fast or irregular heartbeats;

• chest pain, pain spreading to your jaw or shoulder;

• shortness of breath;

• fever, hot flashes, sweating;

• tremors, or if you feel unusually cold;

• weakness, tiredness, sleep problems (insomnia);

• memory problems, feeling depressed or irritable;

• headache, leg cramps, muscle aches;

• feeling nervous or irritable;

• dryness of your skin or hair, hair loss;

• irregular menstrual periods; or

• vomiting, diarrhea, appetite changes, weight changes.

Certain side effects may be more likely in older adults.

Common side effects of levothyroxine may include:

• chest pain, irregular heartbeats;
• shortness of breath;
• headache, leg cramps, muscle pain or weakness;
• tremors, feeling nervous or irritable, trouble sleeping;
• increased appetite;
• feeling hot;
• weight loss;
• changes in your menstrual periods;
• diarrhea; or
• skin rash, partial hair loss.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Many other medicines can be affected by your thyroid hormone levels. Certain other medicines may also increase or decrease the effects of levothyroxine.

Certain medicines can make this medicine less effective if taken at the same time. If you use any of the following drugs, avoid taking them within 4 hours before or 4 hours after you take levothyroxine:

• calcium carbonate (Alka-Mints, Caltrate, Os-Cal, Oyster Shell Calcium, Rolaids Soft Chew, Tums, and others);

• cholestyramine, colesevelam, colestipol;

• ferrous sulfate iron supplement;

• sucralfate;

• sodium polystyrene sulfonate (Kalexate, Kayexalate, Kionex);

• stomach acid reducers - esomeprazole, lansoprazole, omeprazole, rabeprazole, Nexium, Prilosec, Prevacid, Protonix, Zegerid, and others; or

• antacids that contain aluminum or magnesium - Gaviscon, Maalox, Milk of Magnesia, Mintox, Mylanta, Pepcid Complete, and others.

Many drugs can interact with levothyroxine. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed here. Tell your doctor about all your current medicines and any medicine you start or stop using.

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.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.

Levothyroxine starts working right away, but it may take several weeks before you notice that your symptoms improve.

Your dosage will depend on your age, your medical condition, and other factors.

Your physician may need to adjust your dosage if you’re pregnant or if you have heart problems. They may also need to periodically change your dose on the basis of your blood tests.

Most of the time, side effects occur because you’re taking a larger dose than you need. If you experience side effects, your doctor can lower your dose.

Levothyroxine is sometimes used as an “off-label” treatment for subclinical hypothyroidism — a mild, but very common, form of hypothyroidism.