Consumer Drug Information

levothyroxine

Generic Name: levothyroxine (LEE voe thy ROX een)
Brand names: Levothroid, Levoxyl, Synthroid, Unithroid, ...show all 15 brand names.

What is levothyroxine?

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

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

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

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

What is the most important information I should know about levothyroxine?

Since thyroid hormone occurs naturally in the body, almost anyone can take levothyroxine. You should not use this medication if you have had a heart attack, a thyroid disorder called thyrotoxicosis, or an adrenal gland problem that is not controlled by treatment.

Before taking this medication, tell your doctor if you have heart disease, coronary artery disease, anemia (lack of red blood cells), diabetes, problems with your pituitary or adrenal glands, or a history of blood clots.

If you use insulin or take diabetes medicine by mouth, ask your doctor if your dose needs to be changed when you start using levothyroxine.

Different brands of levothyroxine may not work the same. If you get a prescription refill and your new pills look different, talk with your pharmacist or doctor.

It may take several weeks before your body starts to respond to this medication. Do not stop taking this medication suddenly. Even if you feel well, you may still need to take this medicine every day for the rest of your life to replace the thyroid hormone your body cannot produce.

There are many other medicines that can affect levothyroxine. Tell your doctor about all the prescription and over-the-counter medications you use. This includes vitamins, minerals, herbal products, and drugs prescribed by other doctors. Do not start using a new medication without telling your doctor.

What should I discuss with my healthcare provider before taking levothyroxine?

If you use insulin or take diabetes medicine by mouth, ask your doctor if your dose needs to be changed when you start using levothyroxine.

Levothyroxine is in the FDA pregnancy category A. This means that it is safe to use while you are pregnant. It is also safe to use while you are breast-feeding a baby. This drug does pass into breast milk, but it is not expected to be harmful to a nursing infant.

Tell your doctor if you become pregnant during treatment. You may need to increase your dose during pregnancy or if you plan to breast-feed.

In most cases, you will need to take levothyroxine for the rest of your life. Taking levothyroxine over long periods of time may cause bone loss, which can lead to osteoporosis. Talk with your doctor about how this could affect you.

How should I take levothyroxine?

Take levothyroxine exactly as your doctor has prescribed it for you. Do not use more of the medication than recommended. Do not take levothyroxine for longer than your doctor has prescribed.

Your doctor may occasionally change your dose to make sure you get the best results from this medication.

It is very important to take levothyroxine with a full glass (8 ounces) of water. The levothyroxine tablet can dissolve very quickly and swell in the throat, possibly causing choking or gagging. Take this medicine on an empty stomach, 30 minutes before eating. Levothyroxine is usually taken in the morning. Follow your doctor's dosing instructions and try to take this medication at the same time each day.

To be sure this medication is helping your condition, your blood will need to be tested on a regular basis. Your kidney or liver function may also need to be tested. It is important that you not miss any scheduled visits to your doctor.

Tell any doctor or dentist who treats you that you are using levothyroxine.

Store levothyroxine at room temperature away from moisture and heat.

What happens if I miss a dose?

Take the missed dose as soon as you remember. If it is almost time for your next dose, skip the missed dose and take the medicine at the next regularly scheduled time. Do not take extra medicine to make up the missed dose.

What happens if I overdose?

Seek emergency medical attention if you think you have used too much of this medicine.

Overdose symptoms may include chest pain, pounding heartbeat, tremor, shortness of breath, leg cramps, confusion, vomiting, diarrhea, or seizures.

What should I avoid while taking levothyroxine?

Do not change brands or change to a generic levothyroxine drug product without first asking your doctor. Different brands of levothyroxine may not work the same. If you get a prescription refill and your new pills look different, talk with your pharmacist or doctor.

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

Levothyroxine side effects

Stop using levothyroxine and get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat. Call your doctor at once if you have any of these serious side effects:

headache;
sleep problems (insomnia);
nervous or irritable feeling;
fever, hot flashes, sweating;
changes in your menstrual periods;
appetite changes, weight changes;

Less serious side effects may include mild hair loss.

This is not a complete list of side effects and others may occur. Tell your doctor about any unusual or bothersome side effect. You may report side effects to FDA at 1-800-FDA-1088.

Levothyroxine Dosing Information

Usual Adult Dose for Hypothyroidism:

Oral:
The initial dose is 12.5 to 50 mcg orally once a day. The dosage can be increased in 12.5 to 25 mcg/day increments every 2 to 4 weeks. In older patients or in younger patients with a history of cardiovascular disease, the dosage should be increased in 12.5 to 25 mcg increments every 3 to 6 weeks.

Few patients require doses higher than 200 mcg. Inadequate response to doses higher than 200 mcg is rare and may suggest malabsorption, poor patient compliance and/or drug interactions.

Parenteral: The usual IV or IM dose is 50 to 75% of the oral dose.

Usual Adult Dose for TSH Suppression:

Oral:
The initial dose is 50 mcg orally once a day. The dosage may be increased in 25 to 50 mcg increments every 2 to 4 weeks. The typical maintenance dose is 100 to 200 mcg orally once a day.

Parenteral: The usual IV or IM dose is 50 to 75 % of the oral dose.

Usual Adult Dose for Thyroid Suppression Test:

Oral: 2.6 mcg/kg/day for 7 to 10 days.

Parenteral: The usual IV or IM dose is 50 to 75% of the oral dose.

Usual Adult Dose for Myxedema Coma:

The initial dose 300 to 500 mcg IV bolus administered one time. The maintenance dose is 75 to 100 mcg IV once a day until the patient can be converted to oral therapy.

Usual Pediatric Dose for Hypothyroidism:

Oral:
0 to 3 months: 10 to 15 mcg/kg orally once per day.

Increase dosage every 4 to 6 weeks until the desired effect is achieved.

3 to 6 months: 8 to 10 mcg/kg orally once per day.

6 to 12 months: 6 to 8 mcg/kg orally once per day.

1 to 5 years: 5 to 6 mcg/kg orally once per day.

6 to 12 years: 4 to 5 mcg/kg orally once per day.

13 to 18 years but growth and puberty incomplete: 2 to 3 mcg/kg orally once per day.

Patients in which growth and puberty are complete: 1.7 mcg/kg orally once per day.

For chronic or severe hypothyroidism:
Initial dose: 25 mcg orally once per day.

Increase dosage as needed in increments of 25 mcg every 2 to 4 weeks until the desired effect is achieved.

Parenteral:
The usual IV or IM dose is 50 to 75% of the oral dose.

What other drugs will affect levothyroxine?

The following drugs may cause medical problems if you use them with levothyroxine: lithium, amiodarone, or antidepressants. Tell your doctor if you have recently received radiation therapy with iodine (such as I-131).

This list is not complete and there are many other drugs that can interact with levothyroxine. Tell your doctor about all the prescription and over-the-counter medications you use. This includes vitamins, minerals, herbal products, and drugs prescribed by other doctors. Do not start using a new medication without telling your doctor.

Certain medicines can be continued, but they may make levothyroxine less effective if taken at the same time. If you use any of the following drugs, use them at least 4 hours before or 4 hours after you take levothyroxine:

calcium carbonate (Caltrate, Citracal, Oystercal, and others);
ferrous sulfate iron supplement;
sucralfate (Carafate);
sodium polystyrene sulfonate (Kayexalate, Kionex, and others);
antacids that contain aluminum (Amphojel, Gaviscon, Maalox, Mylanta, Riopan, Rulox, Tums, and others); and
cholesterol-lowering drugs cholestyramine (Questran) and colestipol (Colestid).

Where can I get more information?

Your pharmacist can provide more information about levothyroxine.

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.
Every effort has been made to ensure that the information provided by Cerner Multum, Inc. ('Multum') is accurate, up-to-date, and complete, but no guarantee is made to that effect. Drug information contained herein may be time sensitive. Multum information has been compiled for use by healthcare practitioners and consumers in the United States and therefore Multum does not warrant that uses outside of the United States are appropriate, unless specifically indicated otherwise. Multum's drug information does not endorse drugs, diagnose patients or recommend therapy. Multum's drug information is an informational resource designed to assist licensed healthcare practitioners in caring for their patients and/or to serve consumers viewing this service as a supplement to, and not a substitute for, the expertise, skill, knowledge and judgment of healthcare practitioners. The absence of a warning for a given drug or drug combination in no way should be construed to indicate that the drug or drug combination is safe, effective or appropriate for any given patient. Multum does not assume any responsibility for any aspect of healthcare administered with the aid of information Multum provides. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the drugs you are taking, check with your doctor, nurse or pharmacist.