Generic Name: levothyroxine (LEE voe thye ROX een)
Brand Name: Levoxyl, Synthroid, Tirosint, Unithroid, ...show all 16 brand namesLevothroid, Levo-T, Levotabs, Eltroxin, Euthyrox, Levotec, Oroxine, Eutroxsig, L THYROXINE ROCHE, LEVOTHYROX, Evotrox, Thyroxine Sodium Pentahydrate
Medically reviewed on May 4, 2018
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.
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.
Before taking this medicine
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. Tell your doctor if you have:
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).
Tell your doctor if you have ever had:
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 taking levothyroxine);
anemia (lack of red blood cells);
osteoporosis, or low bone mineral density;
problems with your pituitary gland; or
any food or drug allergies.
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.
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 and read all medication guides or instruction sheets. Your doctor may occasionally change your dose. Use the medicine exactly as directed.
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.
Levothyroxine doses are based on weight in children. Your dose needs may change if you gain or lose weight.
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.
You may need frequent medical tests. Tell any doctor, dentist, or surgeon 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 medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take 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.
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?
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.
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:
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;
headache, leg cramps, muscle aches;
feeling nervous or irritable;
dryness of your skin or hair, hair loss;
changes in your menstrual periods; or
Certain side effects may be more likely in older adults.
Common side effects may include:
headache, leg cramps;
tremors, nervousness, trouble sleeping;
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. Certain other medicines may also increase or decrease the effects of 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:
ferrous sulfate iron supplement;
Many drugs can affect levothyroxine. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed here. Tell your doctor about all your current medicines and any medicine you start or stop using.
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.
Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.
Copyright 1996-2018 Cerner Multum, Inc. Version: 12.04.
More about levothyroxine
- Levothyroxine Side Effects
- During Pregnancy or Breastfeeding
- Dosage Information
- Drug Images
- Drug Interactions
- Compare Alternatives
- Support Group
- Pricing & Coupons
- En Español
- 454 Reviews
- Drug class: thyroid drugs
- Levothyroxine Tablets
- Levothyroxine Capsules
- Levothyroxine Injection Solution
- Levothyroxine (Advanced Reading)
- Levothyroxine Injection (Advanced Reading)