Generic Name: levothyroxine (LEE voe thye ROX een)
Brand Name: Levoxyl, Synthroid, Tirosint, Unithroid
What is levothyroxine?
Levothyroxine is a replacement for a hormone 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 may also be used for purposes not listed in this medication guide.
What is the most important information I should know about levothyroxine?
You may not be able to take levothyroxine if you have certain medical conditions. Tell your doctor if you have an untreated or uncontrolled adrenal gland disorder, a thyroid disorder called thyrotoxicosis, or if you have any recent or current symptoms of a heart attack.
Levothyroxine should not be used to treat obesity or weight problems.
What should I discuss with my healthcare provider before taking levothyroxine?
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.
Since thyroid hormone occurs naturally in the body, almost anyone can take levothyroxine. However, you may not be able to take this medicine if you have certain medical conditions.
To make sure levothyroxine is safe for you, tell your doctor if you have:
a thyroid disorder called thyrotoxicosis;
heart disease, coronary artery disease, or a history of blood clots;
diabetes (insulin or oral diabetes medication doses may need to be changed when you start taking levothyroxine);
anemia (lack of red blood cells);
osteoporosis, or low bone mineral density;
problems with your pituitary gland;
any food or drug allergies;
an untreated or uncontrolled adrenal gland disorder; or
if you have recently had a heart attack, or are having any symptoms of a heart attack (chest pain or heavy feeling, pain spreading to the jaw or shoulder, nausea, sweating, general ill feeling).
Tell your doctor if you have recently received radiation therapy with iodine (such as I-131).
Levothyroxine is not expected to harm an unborn baby. If you become pregnant while taking levothyroxine, do not stop taking 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.
Levothyroxine can pass into breast milk, but it is not expected to be harmful to a nursing baby. Tell your doctor if you are breast-feeding. Your dose needs may be different while you are nursing.
Do not give this medicine to a child without medical advice. Tirosint is not approved for use by anyone younger than 6 years old.
How should I take levothyroxine?
Follow all directions on your prescription label. Your doctor may occasionally change your dose. Do not take this medicine in larger or smaller amounts or for longer than recommended.
Levothyroxine works best if you take it on an empty stomach, at least 30 minutes before breakfast. Follow your doctor's dosing instructions and try to take the medicine at the same time each day.
Swallow the tablet or capsule whole, with a full glass (8 ounces) of water. The levothyroxine tablet may dissolve very quickly and could swell in your throat.
If a child is using this medicine, tell your doctor if the child has any changes in weight. Levothyroxine doses are based on weight in children, and any changes may affect your child's dose.
It may take several weeks before your body starts to respond to levothyroxine. Keep using this medicine even if you feel well. You may need to use levothyroxine for the rest of your life.
While using levothyroxine, you may need frequent medical tests. Tell any doctor or dentist who treats you that you are using levothyroxine.
Store at room temperature away from moisture and heat.
Do not share this medicine with another person, even if they have the same symptoms you have.
What happens if I miss a dose?
Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.
What happens if I overdose?
Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.
Overdose symptoms may include headache, leg cramps, tremors, feeling nervous or irritable, chest pain, shortness of breath, and fast or pounding heartbeats.
What should I avoid while taking levothyroxine?
Certain medicines can make levothyroxine less effective if taken at the same time. If you use any of the following drugs, avoid taking them within 4 hours before or 4 hours after you take levothyroxine:
calcium carbonate (Alka-Mints, Calcium Oyster Shell, Caltrate, Os-Cal, Oyster Shell Calcium, Rolaids Soft Chew, Tums, and others);
ferrous sulfate iron supplement;
sodium polystyrene sulfonate (Kalexate, Kayexalate, Kionex); or
antacids that contain aluminum or magnesium--Acid Gone, Gaviscon, Maalox, Milk of Magnesia, Mintox, Mylanta, Pepcid Complete, and others).
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
Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Call your doctor at once if you have a serious side effect such as:
fast or irregular heart rate;
chest pain, feeling short breath;
fever, hot flashes, sweating;
feeling unusually cold;
weakness, tiredness, sleep problems (insomnia);
memory problems, feeling depressed or irritable;
dryness of your skin or hair, hair loss;
changes in your menstrual periods; or
vomiting, diarrhea, appetite changes, weight changes.
Common side effects may include:
leg cramps, muscle weakness;
feeling nervous or irritable;
skin rash, mild hair loss.
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.
See also: Side effects (in more detail)
What other drugs will affect levothyroxine?
Many other medicines can be affected by your thyroid hormone levels. Other medicine may also increase or decrease the effects of levothyroxine.
Many drugs can interact with levothyroxine and not all possible interactions are listed in this medication guide.
Tell your doctor about all medications you use, start using, or stop using during your treatment with levothyroxine. This includes prescription, over-the-counter, vitamin, and herbal products. Give a list of all your medicines to any healthcare provider who treats you.
More about Synthroid (levothyroxine)
- Side Effects
- During Pregnancy or Breastfeeding
- Dosage Information
- Drug Images
- Drug Interactions
- Support Group
- Pricing & Coupons
- En Español
- 126 Reviews – Add your own review/rating
- Drug class: thyroid drugs
Related treatment guides
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.
- Disclaimer: 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.
Copyright 1996-2012 Cerner Multum, Inc. Version: 12.01.
Date modified: July 02, 2017
Last reviewed: May 02, 2017