Brand name:

Levothyroxine

Why is this drug prescribed?

Levothyroxine, a synthetic thyroid hormone, may be given in any of the following cases:

If your own thyroid gland is not making enough hormone;

If you have an enlarged thyroid (a goiter) or are at risk for developing a goiter;

If you have certain cancers of the thyroid;

If your thyroid production is low due to surgery, radiation, certain drugs, or disease of the pituitary gland or hypothalamus in the brain.

Most important fact about this drug

If you are taking levothyroxine to make up for a lack of natural hormone, it is important to take it regularly at the same time every day. You will probably need to take it for the rest of your life.

How should you take this medication?

Take levothyroxine as a single dose, preferably on an empty stomach, one-half to one hour before breakfast. The drug is absorbed better on an empty stomach. Be sure to take the dose with plenty of water.

• If you miss a dose...
  Take it as soon as you remember. If it is almost time for your next dose, skip the one you missed and go back to your regular schedule. Never take 2 doses at the same time. If you miss 2 or more doses in a row, consult your doctor.

• Storage instructions...
  Keep this medication in a tightly closed container. Store it at room temperature, away from light and moisture.

What side effects may occur?

Side effects from levothyroxine, other than overdose symptoms, are rare. People who are treated with levothyroxine may initially lose some hair, but this effect is usually temporary. You may have an allergic reaction such as a rash or hives. Children may have an increase in pressure within the skull. Excessive dosage or a too rapid increase in dosage may lead to overstimulation of the thyroid gland. Notify your doctor immediately if you develop any of the following symptoms.

• Symptoms of overstimulation:
  Abdominal cramps, anxiety, changes in appetite, change in menstrual periods, chest pain, diarrhea, emotional instability, fatigue, fever, flushing, hair loss, headache, heart attack or failure, heat intolerance, hyperactivity, increased heart rate, irregular heartbeat, irritability, muscle weakness, nausea, nervousness, palpitations, shortness of breath, sleeplessness, sweating, tremors, vomiting, weight loss

Why should this drug not be prescribed?

You should not be treated with levothyroxine if you are hypersensitive to thyroid hormone; your thyroid gland is making too much thyroid hormone; you have had a recent heart attack; or your adrenal glands are not making enough corticosteroid hormone. If you are sensitive to dyes, ask your doctor for a levothyroxine formulation that is made without color additives.

Although levothyroxine will speed up your metabolism, it is not effective as a weight-loss drug and should not be used as such. An overdose may cause life-threatening side effects, especially if you take levothyroxine with an appetite-suppressant medication.

Special warnings about this medication

Levothyroxine has profound effects on the body. Make sure your doctor is aware of all your medical problems, especially heart disease, clotting disorders, diabetes, and disorders of the adrenal or pituitary glands. The doctor will also need to know about any allergies you may have to food or medicine, and will ask for the names of any medications you take, whether prescription or over-the-counter.

You should receive low doses of levothyroxine, under very close supervision, if you are an older person, or if you suffer from high blood pressure, angina (chest pain caused by a heart condition), or other types of heart disease. If you develop chest pain or additional circulatory problems, your dosage may have to be reduced.

If you have diabetes, or if your body makes insufficient adrenal corticosteroid hormone, levothyroxine will tend to make your symptoms worse. If you take medication for any of these disorders, the dosage will probably have to be adjusted once you begin taking levothyroxine. If diabetes is the problem, you should immediately report to your doctor any change in your glucose readings.

Postmenopausal women on long-term levothyroxine therapy may suffer a loss of bone density, increasing the danger of osteoporosis (brittle bones). To minimize the loss, the doctor will prescribe the lowest dosage needed to control symptoms of thyroid deficiency.

Levothyroxine may cause seizures at the beginning of treatment, although this is rare. You may also notice some hair loss at first, but this is temporary.

It may take a few weeks for levothyroxine to begin working, and you may not see any change in your symptoms until then.

Tell your doctor or dentist you are taking levothyroxine before you have surgery of any kind.

Tell your doctor if you become pregnant while you are taking levothyroxine. Your dose may need to be increased.

Excessive doses of levothyroxine in infants may cause the top of the skull to close too early. In children, overtreatment can stunt growth.

Possible food and drug interactions when taking this medication

Levothyroxine can interact with a wide variety of medications. It's advisable to check with your doctor before taking any other drug, but you should be especially wary of the following:

Amiodarone

Androgens (male hormones)

Antacids and anti-gas medications

Antidepressants

Blood pressure drugs

Blood-thinning drugs such as warfarin and heparin

Chloral hydrate (a sedative)

Cholesterol-lowering drugs

Diabetes drugs, including insulin

Digitalis-type drugs such as digoxin

Estrogen products and oral contraceptives

Furosemide

Growth hormones

Hormone inhibitors

Immune system drugs such as interferon and interleukin

Iodide

Iron supplements

Kayexalate

Ketamine

Lithium

Methadone and heroin

Metoclopramide

Nonsteroidal anti-inflammatory drugs such as phenylbutazone and aspirin

Parkinson's drugs

Propylthiouracil (a thyroid inhibitor)

Seizure medications

Steroids such as dexamethasone and hydrocortisone

Stimulants such as epinephrine

Sucralfate

The cancer drugs 5-fluorouracil, 6-mercaptopurine, mitotane, and tamoxifen

The tranquilizers perphenazine and diazepam

The tuberculosis drugs aminosalicylate, rifampin, and ethionamide

Theophylline

A high-fiber diet, soy-containing supplements, and walnuts can also interfere with the effects of levothyroxine.

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Special information if you are pregnant or breastfeeding

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If you need to take levothyroxine because of a thyroid hormone deficiency, you can continue to take the medication during pregnancy. In fact, your doctor will test you regularly and may increase your dose. Once your baby is born, you may breastfeed while continuing to take carefully regulated doses of levothyroxine.

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Recommended dosage

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Your doctor will tailor the dosage to meet your individual requirements, taking into consideration the status of your thyroid gland and other medical conditions you may have. Older adults often require somewhat smaller doses. To make sure the dosage is right for you, the doctor will monitor your thyroid hormone level with periodic blood tests.

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Overdosage

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An overdose of levothyroxine can produce the same symptoms of overstimulation listed under "What side effects may occur?" Confusion and disorientation are also possible, and there have been reports of stroke, shock, coma, and death. If you suspect a massive overdose, seek emergency medical attention immediately.