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Tirosint

Generic Name: levothyroxine (LEE voe thye ROX een)
Brand Name: Levoxyl, Synthroid, Tirosint, Unithroid

Medically reviewed on November 6, 2017.

What is Tirosint?

Tirosint is a replacement for a hormone normally produced by your thyroid gland to regulate the body's energy and metabolism. This medicine is given when the thyroid does not produce enough of this hormone on its own.

Tirosint treats hypothyroidism (low thyroid hormone). This medicine is also used to treat or prevent goiter (enlarged thyroid gland), which can be caused by hormone imbalances, radiation treatment, surgery, or cancer.

Tirosint may also be used for purposes not listed in this medication guide.

Important Information

You may not be able to take Tirosint 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.

Tirosint should not be used to treat obesity or weight problems.

Before taking this medicine

Tirosint 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.

Since thyroid hormone occurs naturally in the body, almost anyone can take Tirosint. However, you may not be able to take this medicine 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

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

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

  • heart disease, coronary artery disease, a heart attack, or a blood clot;

  • diabetes (insulin or oral diabetes medication doses may need to be changed when you start taking Tirosint);

  • anemia (lack of red blood cells);

  • a blood-clotting disorder;

  • osteoporosis, or low bone mineral density;

  • problems with your pituitary gland; or

  • any food or drug allergies.

Tell your doctor if you have recently received radiation therapy with iodine (such as I-131).

Tirosint is not expected to harm an unborn baby. If you become pregnant while taking this medicine, 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.

Levothyroxine can pass into breast milk, but it is not expected to be harmful to a nursing baby. Tell your doctor if you are breast-feeding. 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.

How should I take Tirosint?

Follow all directions on your prescription label. Your doctor may occasionally change your dose. Do not take this medicine in larger or smaller amounts or for longer than recommended.

Tirosint works best if you take it on an empty stomach, at least 30 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 Tirosint tablet may dissolve very quickly and could swell in your throat.

If a child is using this medicine, tell your doctor if the child has any changes in weight. Tirosint doses are based on weight in children, and any changes may affect your child's dose.

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

While using Tirosint, 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.

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

What happens if I miss a dose?

Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

What happens if I overdose?

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.

What should I avoid while taking Tirosint?

Certain medicines can make Tirosint 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 this medicine:

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

Tirosint side effects

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

Call your doctor at once if you have a serious side effect such as:

  • fast or irregular heart rate;

  • chest pain, feeling short breath;

  • fever, hot flashes, sweating;

  • feeling 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;

  • changes in your menstrual periods; or

  • vomiting, diarrhea, appetite changes, weight changes.

Certain side effects may be more likely in older adults.

Common side effects may include:

  • muscle weakness;

  • headache;

  • diarrhea; or

  • skin rash, mild 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.

See also: Side effects (in more detail)

What other drugs will affect Tirosint?

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

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

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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