Generic name: levothyroxine (oral/injection) [ LEE-voe-thye-ROX-een ]
Brand names: Ermeza, Euthyrox, Levo-T, Levoxyl, Synthroid, ... show all 9 brands Thyquidity, Tirosint, Tirosint-Sol, Unithroid
Drug class: Thyroid drugs

Medically reviewed by Carmen Pope, BPharm. Last updated on Jan 4, 2024.

What is levothyroxine?

Levothyroxine is used in adults and children to treat hypothyroidism (underactive thyroid - a condition where the thyroid gland does not produce enough thyroid hormone).

Levothyroxine is also used in adults along with surgery and radioactive iodine therapy to treat a certain type of thyroid cancer.

Levothyroxine injection is used in adults to treat myxedema coma.

Levothyroxine belongs to a class of medications called hormones. It works by replacing thyroid hormone that is normally produced by the body.

Without thyroid hormone, your body cannot function properly, which may result in poor growth, slow speech, lack of energy, excessive tiredness, constipation, weight gain, hair loss, dry, thick skin, increased sensitivity to cold, joint and muscle pain, heavy or irregular menstrual periods, and depression. When taken correctly, levothyroxine reverses these symptoms.

Levothyroxine side effects

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:

• sudden pain or trouble moving your hip, wrist, or back;

• fast or irregular heartbeats;

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

• wheezing;

• fever, swollen glands, itching, joint pain, or not feeling well;

• nausea, vomiting, or diarrhea; or

• high blood sugar - increased thirst, increased urination, dry mouth, fruity breath odor.

Common levothyroxine side effects may include:

• fever, hot flashes, increased sweating;

• tiredness;

• skin rash, hair loss;

• chest pain, fast or irregular heartbeats, shortness of breath;

• headache, leg cramps, muscle pain or weakness;

• tremors, feeling nervous or irritable, sleep problems (insomnia);

• increased or change in appetite;

• weight loss or weight gain;

• changes in your menstrual periods; or

• vomiting, diarrhea.

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.

Related/similar drugs

Warnings

You may not be able to use levothyroxine if you have certain medical conditions. Tell your doctor if you have an untreated or uncontrolled adrenal gland disorder or any heart problems such as a recent 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.

Taking more than your recommended dose will not make this medicine more effective, and may cause serious side effects.

Before taking this medicine

You should not use levothyroxine if you are allergic to glycerin or edetate disodium, or if you have an untreated or uncontrolled adrenal gland disorder.

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

• a thyroid nodule;

• thyroiditis (inflammation of thyroid gland);

• heart problems such as a heart attack, stroke;

• a blood clot or a 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 or adrenal gland;

• an allergy to any food or drugs;

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

• kidney disease.

Tell your doctor if you are pregnant or plan to become pregnant. Having hypothyroidism during pregnancy may increase the risk of premature birth or other complications. The benefit of treating hypothyroidism may outweigh any risks to the 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.

You may be more likely to have a broken bone while using levothyroxine. Talk with your doctor about ways to keep your bones healthy.

How should I use levothyroxine?

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

Some brands of levothyroxine have different dosage instructions and/or recommendations of how soon you need to take them before eating food. Always check the instructions on the label.

Oral levothyroxine

Oral levothyroxine is taken by mouth and is available as tablets, capsules, and an oral solution.

• Keep using this medicine even if you feel well. You may not fully benefit from this medicine for several weeks.
• You will need frequent medical tests, and your next dose may be delayed based on the results.
• This medicine can affect the results of certain medical tests. Tell any doctor who treats you that you are using this medicine.
• Tell your doctor if you have a planned surgery or dental procedure.
• Taking more than your recommended dose will not make this medicine more effective, and may cause serious side effects.

Tablets and capsules

Take levothyroxine tablets and capsules on an empty stomach, at least 30 to 60 minutes before breakfast with a full glass of water. Take the medicine at the same time each day.

• Swallow the capsule whole and do not crush, chew, break, or open it. Tell your doctor if your child cannot swallow a capsule whole.
• If you cannot swallow a tablet whole, crush the tablet, and mix it with 1 or 2 teaspoons of water; give the mixture right away. Do not save it for later use.
• Keep each tablet or capsule in the blister pack until you are ready to take one.
• Store at room temperature away from moisture, heat, and light.

Oral solution (liquid medicine)

Measure liquid medicine with the supplied measuring device (not a kitchen spoon).

• Dosages are based on weight in children and teenagers. Your child's dose may change if the child gains or loses weight.
• Your dose needs may change if you switch to a different brand, strength, or form of levothyroxine. Avoid medication errors by using only the medicine your doctor prescribes.
• Tirosint-Sol oral solution can be administered 15 minutes before eating breakfast. Use it within 3 months after opening the pouch.
• Ermeza and Thyquidity liquids should be taken on an empty stomach, at least 30 to 60 minutes before breakfast. Store them in their original bottle. Use Ermeza within 90 days and Thyquidity within 8 weeks of opening the bottle.
• Store at room temperature away from moisture, heat, and light.

Intravenous levothyroxine

This is given as an injection into a vein by a healthcare provider and should only be used to treat myxedema coma.

What happens if I miss a dose?

In a medical setting, you are not likely to miss a dose of levothyroxine injection.

Take the missed oral levothyroxine dose as soon as you remember, and then go back to your regular schedule. Do not use two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose can be fatal.

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

What should I avoid while using levothyroxine?

Avoid the following food products within 1 hour of taking oral levothyroxine or the medication will not be as effective: grapefruit juice, infant soy formula, soybean flour, cotton seed meal, walnuts, and high-fiber foods.

What other drugs will affect levothyroxine?

Sometimes it is not safe to use certain medicines at the same time. Some drugs can affect your thyroid hormone levels and also make levothyroxine less effective.

If you use any of the following drugs, avoid taking them within 4 hours before or 4 hours after you use levothyroxine:

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

• sevelamer, lanthanum;

• cholestyramine, colesevelam, colestipol;

• iron supplements;

• sucralfate;

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

• stomach acid reducers - esomeprazole, lansoprazole, omeprazole, rabeprazole, Nexium, Prilosec, Prevacid, Protonix, Zegerid, and others (this applies to most brands of levothyroxine except for Tirosint-SOL); or

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

Tell your doctor about all your other medicines, especially:

• orlistat;

• phenobarbital, rifampin;

• ketamine, steroid medicines;

• antidepressants such as amitriptyline or maprotiline;

• heart or blood pressure medication;

• diabetes medications;

• cancer medicine such as imatinib; or

• a blood thinner - warfarin, Coumadin, Jantoven.

This list is not complete and many other drugs may interact with levothyroxine. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.

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Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use levothyroxine 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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