Levothyroxine (Synthroid)

Levothyroxine (Synthroid)

Levothyroxine is a medicine used to treat people with hypothyroidism.

Hypothyroidism means a person’s thyroid gland doesn’t make enough thyroid hormone. People with this condition may no longer have a functioning thyroid, or hypothyroidism can be caused by a variety of other reasons that affect thyroid hormone production.

Levothyroxine is also used to prevent or treat a goiter (an enlarged thyroid gland) or with other therapies to treat thyroid cancer.

This drug is a hormone, which works by replacing thyroid hormone that your body normally produces.

The U.S. Food and Drug Administration (FDA) initially approved this medicine in 1969. It’s marketed under various brands.

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What is Levothyroxine (Synthroid) used for?

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What is the most important information I should know about Levothyroxine (Synthroid)?

Levothyroxine should not be used to treat obesity or weight problems. Dangerous side effects or death can occur from the misuse of levothyroxine, especially if you are taking any other weight-loss medications or appetite suppressants.

If you become pregnant while using levothyroxine, do not stop using 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.

Tell your doctor if you are breastfeeding. Your dose needs may be different while you are nursing.

Do not give this medicine to a child without medical advice. is not approved for use by anyone younger than 6 years old. Tirosint

Since thyroid hormone occurs naturally in the body, almost anyone can use levothyroxine. However, Tell your doctor if you have: you may not be able to use this medicine if you have certain medical conditions.

Tell your doctor if you have ever had:

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

  • 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).
  • a thyroid nodule;
  • heart disease, a blood clot, or a blood-clotting disorder;
  • diabetes (insulin or oral diabetes medication doses may need to be changed when you start using levothyroxine);
  • kidney disease;
  • anemia (lack of red blood cells);
  • osteoporosis, or low bone mineral density;
  • problems with your pituitary gland; or
  • any food or drug allergies.
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Side Effects

What are the side effects of Levothyroxine (Synthroid)?

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

Call your doctor at once if you have:

Certain side effects may be more likely in older adults.

  • fast or irregular heartbeats;
  • chest pain, pain spreading to your jaw or shoulder;
  • shortness of breath;
  • fever, hot flashes, sweating;
  • tremors, or if you feel 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;
  • irregular menstrual periods; or
  • vomiting, diarrhea, appetite changes, weight changes.
  • chest pain, irregular heartbeats;
  • shortness of breath;
  • headache, leg cramps, muscle pain or weakness;
  • tremors, feeling nervous or irritable, trouble sleeping;
  • increased appetite;
  • feeling hot;
  • weight loss;
  • changes in your menstrual periods;
  • diarrhea; or
  • skin rash, partial hair loss.

Common side effects may include:

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.

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Pregnancy & Breastfeeding

Can I take Levothyroxine (Synthroid) if I’m pregnant or breastfeeding?

If you become pregnant while using levothyroxine, do not stop using 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.

Tell your doctor if you are breastfeeding. Your dose needs may be different while you are nursing.

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What drugs and food should I avoid while taking Levothyroxine (Synthroid)?

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

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Dosage Guidelines & Tips

How to take Levothyroxine (Synthroid)?

Use Levothyroxine (Synthroid) exactly as directed on the label, or as prescribed by your doctor. Do not use in larger or smaller amounts or for longer than recommended.

Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose. Use the medicine exactly as directed.

Levothyroxine is taken by mouth. Levothyroxine is given as an infusion into a vein. Levothyroxine is usually given by injection only if you are unable to take the medicine by mouth. oralinjection

Measure carefully. Use the dosing syringe provided, or use a medicine dose-measuring device (not a kitchen spoon). liquid medicine

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

You may need frequent medical tests. Tell any doctor, dentist, or surgeon who treats you that you are using levothyroxine.

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

Levothyroxine works best if you take it on an empty stomach, 30 to 60 minutes before breakfast. Follow your doctor's dosing instructions and try to take the medicine at the same time each day. oral

Swallow the or whole, with a full glass (8 ounces) of water. The levothyroxine tablet may dissolve very quickly and could swell in your throat. tabletcapsule

Levothyroxine doses are based on weight in children. Your child's dose needs may change if the child gains or loses weight.

Store at room temperature away from moisture and heat. Use within 3 months after opening the pouch. Tirosint-Sol

What should I do if I missed a dose of Levothyroxine (Synthroid)?

Use the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. use two doses at one time. Do not

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Overdose Signs

What happens if I overdose on Levothyroxine (Synthroid)?

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

If you think you or someone else may have overdosed on: Levothyroxine (Synthroid),  call your doctor or the Poison Control center
(800) 222-1222
If someone collapses or isn't breathing after taking Levothyroxine (Synthroid), call 911
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What to Expect

Levothyroxine starts working right away, but it may take several weeks before you notice that your symptoms improve.

Usually, treatment with levothyroxine is lifelong. If you stop taking it, your symptoms will return.
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Additional Dosage Information

Your dosage will depend on your age, your medical condition, and other factors.

Your physician may need to adjust your dosage if you’re pregnant or if you have heart problems. They may also need to periodically change your dose on the basis of your blood tests.

Most of the time, side effects occur because you’re taking a larger dose than you need. If you experience side effects, your doctor can lower your dose.

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Secondary Uses

Levothyroxine is sometimes used as an “off-label” treatment for subclinical hypothyroidism — a mild, but very common, form of hypothyroidism.

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Medical Disclaimer

Drugs A-Z provides drug information from Everyday Health and our partners, as well as ratings from our members, all in one place. Cerner Multum™ provides the data within some of the Overview, Uses, Warnings, Side Effects, Pregnancy, Interactions, Dosage, Overdose, and Images sections. The information within all other sections is proprietary to Everyday Health.