Levothyroxine, a synthetic thyroid hormone, is taken for a variety of thyroid problems. It is best taken on an empty stomach, 30 to 60 minutes before breakfast.

Levothroid Overview

Reviewed: December 12, 2012

Levothyroxine is a prescription medication used to treat underactive thyroid (hypothyroidism) and other thyroid problems. Levothroxine is a synthetic thyroid hormone, which replaces the body's reduced levels of natural thyroid hormone.

This medication comes in tablet form and is taken once in the morning on an empty stomach, with a glass of water.

Common side effects of levothyroxine include tremors, change in appetite, and irregular heartbeats.


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  • Other
  • Goiter
  • Hypothyroidism
  • Myxedema
  • Thyroid Neoplasms
  • Thyroiditis, Autoimmune

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Levothroid Cautionary Labels


Uses of Levothroid

Levothyroxine, a synthetic thyroid hormone, is a prescription medication used as a replacement or supplemental therapy in hypothyroidism, a condition in which the thyroid gland does not produce enough thyroid hormone. This medication is also used to treat nodules and goiters, as well as some types of thyroid cancer.

This medication may be prescribed for other uses. Ask your doctor or pharmacist for more information.


Levothroid Drug Class

Levothroid is part of the drug class:

Side Effects of Levothroid

Too much levothyroxine can cause symptoms of hyperthyroidism. If you experience the following symptoms, call your doctor right away as your dosage may need to be reduced:

  • rapid or irregular heartbeat or pulse
  • heart palpitations
  • chest pain
  • difficulty breathing
  • leg cramps
  • headache
  • nervousness
  • irritability
  • sleeplessness
  • tremors
  • change in appetite
  • weight gain or loss
  • vomiting
  • diarrhea
  • excessive sweating
  • heat intolerance
  • fever
  • changes in menstrual periods
  • hives or skin rash
  • any other unusual medical event

Levothyroxine can cause allergic reactions. Symptoms include:

  • wheezing
  • difficulty breathing
  • hives
  • itching
  • swelling of lips, mouth, throat

Call your doctor right away if you experience symptoms of allergic reaction.

This is not a complete list of levothyroxine side effects. Ask your doctor or pharmacist for more information.

Levothroid Interactions

Tell your doctor about all the medicines you take including prescription and non-prescription medicines, vitamins, and herbal supplements. Many medicines affect the absorption and metabolism of levothyroxine and may change the way your body responds to levothyroxine. Additionally, levothyroxine has effects on the way your body responds to other medicines. The following medicines may interact with levothyroxine:

  • amphetamines
  • anticoagulants ('blood thinners') such as warfarin (Coumadin)
  • antidepressants or anti-anxiety agents
  • arthritis medicine
  • aspirin 
  • beta-blockers such as metoprolol (Lopressor, Toprol), propranolol (Inderal) or timolol (Blocadren, Timoptic) 
  • cancer chemotherapy agents
  • diabetes medications (insulin and tablets)
  • digoxin (Lanoxin)
  • estrogens 
  • methadone
  • oral contraceptives 
  • phenytoin (Dilantin)
  • steroids
  • theophylline (TheoDur)
  • vitamins
  • antacids
  • cholestyramine (Questran)
  • colestipol (Colestid)
  • iron 
  • orlistat (Alli, Xenical)
  • simethicone (Phazyme, Gas X)
  • sodium polystrene sulfonate (Kayexalate)
  • sucralfate (Carafate)

This is not a complete list of levothyroxine drug interactions. Ask your doctor or pharmacist for more information.

Levothroid Precautions

You should not take levothyroxine if you:

  • are allergic to any ingredient in the medication
  • have hyperthyroidism (overactive thyroid)
  • have a low TSH
  • have untreated adrenal insufficiency
  • have had a heart attack

Use levothyroxine only as prescribed by your physician. Do not discontinue or change the amount you take or how often you take it, unless directed to do so by your physician.

It may take several weeks before you notice an improvement in your symptoms.

Tell your doctor if you become pregnant while taking levothyroxine. It is likely that your dose of levothyroxine will need to be increased while you are pregnant.

Notify your doctor or dentist that you are taking this medicine prior to any surgery.

Partial hair loss may occur rarely during the first few months of levothyroxine therapy, but this is usually temporary.

Levothyroxine should not be used as a weight loss medication in people without hypothyroidism.

Iron and calcium supplements and antacids can decrease the absorption of levothyroxine. Therefore, levothyroxine should not be administered within 4 hrs of these products.

Levothyroxine may increase your risk of developing osteoporosis, especially if your levothyroxine dose is too high.

Levothroid Food Interactions

Medicines can interact with certain foods. In some cases, this may be harmful and your doctor may advise you to avoid certain foods. In the case of levothyroxine there are no specific foods that you must exclude from your diet when receiving levothyroxine.

Inform MD

Before taking levothyroxine tell your doctor:

  • if you are allergic to levothyroxine or any foods or medicines
  • if you are pregnant or intend to become pregnant, or if you are breastfeeding
  • if you have heart disease, diabetes, clotting disorders, or adrenal and pituitary gland problems. Your dose of medications used to control these other conditions may need to be adjusted while you are taking levothyroxine. If you have diabetes, monitor your blood and/or urinary glucose levels as directed by your doctor and tell your doctor right away if there are any changes. If you are taking anticoagulants (blood thinners), your clotting status should be checked frequently.

Tell your doctor about all the medicines you take including prescription and non-prescription medicines, vitamins, and herbal supplements.

Levothroid and Pregnancy

Tell your doctor if you are pregnant or plan to become pregnant. Studies in women taking levothyroxine during pregnancy have shown it is safe for use during pregnancy. It does not appear to cause harm to the unborn baby. In fact, it is important to treat hypothyroidism (underactive thyroid) during pregnancy, as undertreatment can be dangerous. Pregnant women often require higher doses of levothyroxine.

Levothroid and Lactation

Tell your doctor if you are breastfeeding or plan to breastfeed. Small amounts of levothyroxine are excreted in human breastmilk, just as natural thyroid hormone passes through breast milk. However, women who don't have enough thyroid hormone may not be capable of lactation (secretion or formation of milk).

Levothroid Usage

Levothyroxine is a tablet that is taken by mouth, usually once a day. It should be taken with a full glass of water. Take levothyroxine in the morning on an empty stomach, at least one-half hour to one hour before eating any food. Iron and calcium supplements and antacids can decrease the absorption of levothyroxine tablets. Take these products at least 4 hours before or 4 hours after you take levothyroxine.

If needed, levothyroxine tablets can be crushed and mixed in 1 to 2 teaspoons of plain water. This mixture must be taken right away.

If you forget a dose of levothyroxine, take the missed dose as soon as you remember it. If it is almost time for your next dose, skip the missed dose. Do not take a double dose of this medication.

Note: if you are prescribed levothyroxine in capsule form, you must swallow them whole. Never crush these capsules.

Levothroid Dosage

Dosing of levothyroxine must be individualized. Your doctor will determine the best levothyroxine dose for you, which will likely be carefully and slowly adjusted. Regular blood tests will be required to monitor your progress. Follow the directions on your prescription label carefully. Do not take more or less than prescribed. It may take several weeks before you begin to notice a change in your symptoms. Do not stop taking levothyroxine without talking to your doctor.

Levothroid Overdose

If you take too much levothyroxine, call your local Poison Control Center or seek emergency medical attention right away.

Other Requirements

Store levothyroxine away from heat, moisture, and light.

Keep this and all medicines out of the reach of children.

Levothroid FDA Warning

WARNING: Thyroid hormones, including Levothyroxine Sodium Tablets, USP, either alone or with other therapeutic agents, should not be used for the treatment of obesity for weight loss. In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction. Larger doses may produce serious or even life threatening manifestations of toxicity, particularly when given in association with sympathomimetic amines such as those used for their anorectic effects.