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Levothyroxine (Synthroid): Uses, Side Effects and Dosage

Updated:
Facts
Status:
Prescription (Rx) Boxed warning
Strength:
175 mcg, 125 mcg, 137 mcg, 150 mcg, 200 mcg, 13 mcg, 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg
Brand names:
Drug class:
Active ingredient:

Source: FDA drug labeling via NLM DailyMed · About this document

Patient information: uses, side effects, how to take - Levothyroxine

What is the most important information I should know about Levothyroxine Sodium capsules?

  • Do not use Levothyroxine Sodium capsules to treat weight problems or weight loss.
  • Do not take more Levothyroxine Sodium capsules than your doctor prescribes for you to take. Over dosage or taking too much Levothyroxine Sodium capsules may cause life-threatening side effects or death.

What are Levothyroxine Sodium capsules?

Levothyroxine Sodium capsules are a prescription medicine that contains a hormone called levothyroxine which is normally produced by the thyroid gland. Levothyroxine Sodium capsules are used to treat adults and children 6 years of age or older:

  • to replace or give extra levothyroxine in people whose thyroid does not produce enough of this hormone.
  • who need surgery and radioiodine therapy to manage a type of thyroid cancer called thyroid-dependent well-differentiated thyroid cancer.

Levothyroxine Sodium capsules should not be used to treat people who are recovering from swelling of the thyroid gland (thyroiditis) and whose bodies do not produce enough levothyroxine for a short time.

Levothyroxine Sodium capsules are unsuitable for children less than 6 years of age or who may be unable to swallow an intact capsule.

Do not take Levothyroxine Sodium capsules:

  • if your adrenal glands are not working well and you have not been treated for this problem.

Before you take Levothyroxine Sodium capsules, tell your doctor about all of your medical conditions, including if you:

  • have or had heart problems.
  • have or had thyroid nodules.
  • have kidney or pituitary gland problems.
  • have any food or drug allergies.
  • have a low red blood cell count (anemia).
  • have diabetes.
  • have weak bones (osteoporosis).
  • have or had a history of blood clotting problems.
  • have recently received radiation therapy with iodine (such as I-131).

  • are pregnant or plan to become pregnant. Levothyroxine Sodium capsules may harm your unborn baby. Your doctor may need to change your Levothyroxine Sodium capsules dose while you are pregnant.

  • are breastfeeding. Levothyroxine sodium capsules can pass into your milk. Talk to your doctor about the best way to feed your baby if you take Levothyroxine Sodium capsules.

Tell your doctor about all the medicines you take including prescription and over-the-counter medicines, vitamins, and herbal supplements. Levothyroxine Sodium capsules may affect the way other medicines work, and other medicines may affect how Levothyroxine Sodium capsules works. You can ask your doctor or pharmacist for a list of medicines that interact with Levothyroxine Sodium capsules.

How should I take Levothyroxine Sodium capsules?

  • Take Levothyroxine Sodium capsules exactly as your doctor tells you to take it.
  • Your doctor will tell you how much Levothyroxine Sodium capsules to take each day.
  • Swallow Levothyroxine Sodium capsules whole. Do not cut, crush, or chew Levothyroxine Sodium capsules before swallowing. If you or your child cannot swallow Levothyroxine Sodium capsules whole, tell your doctor. You may need a different medicine.
  • Your doctor may change your dose, if needed.

  • Take your dose of Levothyroxine Sodium capsules 1 time each day, 30 minutes to 1 hour before breakfast, on an empty stomach.

  • Certain medicines can interfere with how Levothyroxine Sodium capsules are absorbed by your body. Take Levothyroxine Sodium capsules:

    • at least 4 hours before or after you take medicines that contain calcium carbonate or iron (ferrous sulfate).
    • at least 4 hours before you take medicines that contain bile acid sequestrants or ion exchange resins.
  • Know the medicines that you take. Ask your doctor or pharmacist for a list of these medicines, if you are not sure.
  • Certain foods including soybean flour, cotton seed meal, walnuts, and dietary fiber can affect your treatment and dose of Levothyroxine Sodium capsules. Talk to your doctor if you eat or drink these foods.
  • Do not remove Levothyroxine Sodium capsules from the original blister package until you are ready to take them.
  • Your doctor should do certain blood tests while you are taking Levothyroxine Sodium capsules and may change your daily dose of Levothyroxine Sodium capsules as needed. You should not stop taking Levothyroxine Sodium capsules or change your dose unless your doctor tells you to.
  • It may take weeks before you notice your symptoms getting better. Keep using this medicine even if you feel well.
  • If you take too much Levothyroxine Sodium capsules or overdose, call your doctor or poison control center at 1-800-222-1222, or go to the nearest hospital emergency room right away.

What are the possible side effects of Levothyroxine Sodium capsules?

Levothyroxine Sodium capsules may cause serious side effects, including:

  • heart problems. You may experience an increased heart rate, chest pain and irregular heartbeat. Your risk of developing heart problems may be greater if you are elderly, have heart problems, or if you take too much Levothyroxine Sodium capsules. Your doctor may reduce your dose or stop treatment with Levothyroxine Sodium capsules for a while if you develop heart problems.
  • worsening diabetic control. If you are diabetic, it may be harder to control your blood sugar levels causing hyperglycemia while taking Levothyroxine Sodium capsules. Check your blood sugar levels closely after starting, changing, or stopping treatment with Levothyroxine Sodium capsules. Your doctor may have to change your diabetes treatment plan.
  • weak or brittle bones. Your risk of developing weak or brittle bones may be greater if you are post-menopausal or you take too much Levothyroxine Sodium capsules.

The most common side effects of Levothyroxine Sodium capsules include:

  • irregular heartbeat
  • chest pain
  • shortness of breath
  • leg cramps
  • headache
  • nervousness
  • hives or skin rash
  • irritability
  • sleep problems (insomnia)
  • tremors
  • muscle weakness
  • change in appetite
  • weight loss
  • vomiting
  • diarrhea
  • sweating a lot
  • heat intolerance
  • fever
  • changes in menstrual period

Other side effects may include:

  • partial hair loss during the first months of treatment with Levothyroxine Sodium capsules. This usually lasts a short period of time (temporary).

These are not all the possible side effects of Levothyroxine Sodium capsules. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

You may also report side effects to YARAL Pharma, Inc at 1-866-218-9009 or www.fda.gov/medwatch.

How should I store Levothyroxine Sodium capsules?

  • Store Levothyroxine Sodium capsules at room temperature between 68°F to 77°F (20°C to 25°C).
  • Store Levothyroxine Sodium capsules away from heat, light, and moisture.
  • Keep Levothyroxine Sodium capsules in the original blister pack until you are ready to use it.

Keep Levothyroxine Sodium capsules and all medicines out of the reach of children.

General information about the safe and effective use of Levothyroxine Sodium capsules

Medicines are sometimes prescribed for purposes other than those listed in a Patient Information leaflet. Do not use Levothyroxine Sodium capsules for a condition for which it was not prescribed. Do not give Levothyroxine Sodium capsules to other people, even if they have the same symptoms that you have. It may harm them. You can ask your pharmacist or doctor for information about Levothyroxine Sodium capsules that is written for health professionals.

What are the ingredients in Levothyroxine Sodium capsules?

Active ingredient: levothyroxine sodium

Inactive ingredients: gelatin, glycerin, and water

Manufactured by: IBSA Institut Biochimique SA, 6912 Pazzallo, Switzerland;

Distributed by: YARAL Pharma, Parsippany, NJ 07054, USA

For more information, call 1-866-218-9009.

About this document

Source: FDA drug labeling via NLM DailyMed · Application number: NDA AUTHORIZED GENERIC 021924 · View the label on DailyMed

Revision date stated in the text: October 2022

Found a mistake? Write to us via the contact page.

The information on this site does not replace the advice of a doctor or pharmacist.

Drug information for Levothyroxine

Rx or OTC
Prescription (Rx)?
  • This drug is available only with a prescription from a licensed healthcare provider.
  • Rx
Boxed warning Yes – this drug has a boxed warning (also called a black box warning), the strongest warning of the FDA.
Drug class l-Thyroxine
Active ingredient Levothyroxine sodium
Dosage form Capsule
Route Oral
Marketing status listed in the FDA NDC Directory
Company (applicant) IBSA
FDA approval NDA AUTHORIZED GENERIC 021924NDA authorized generic Approved October 13, 2006
Reference listed drug This is the reference listed drug (RLD) that generics are compared with.
Manufacturers 12 labelers list this drug on DailyMed
Recalls
  • August 6, 2026: Class II recall: Subpotent Drug
  • August 6, 2026: Class II recall: Subpotent Drug
  • August 6, 2026: Class II recall: Subpotent Drug
Show more recalls (2)+
  • August 6, 2026: Class II recall: Subpotent Drug
  • August 6, 2026: Class II recall: Subpotent Drug
Packages (NDC)
Package
175 mcg – 10 in 1 blister pack / 3 in 1 carton NDC 82347-0055-4
125 mcg – 10 in 1 blister pack / 3 in 1 carton NDC 82347-0040-4
137 mcg – 10 in 1 blister pack / 3 in 1 carton NDC 82347-0045-4
150 mcg – 10 in 1 blister pack / 3 in 1 carton NDC 82347-0050-4
200 mcg – 10 in 1 blister pack / 3 in 1 carton NDC 82347-0060-4
13 mcg – 10 in 1 blister pack / 3 in 1 carton NDC 82347-0005-4
25 mcg – 10 in 1 blister pack / 3 in 1 carton NDC 82347-0010-4
50 mcg – 10 in 1 blister pack / 3 in 1 carton NDC 82347-0015-4
75 mcg – 10 in 1 blister pack / 3 in 1 carton NDC 82347-0020-4
88 mcg – 10 in 1 blister pack / 3 in 1 carton NDC 82347-0025-4
100 mcg – 10 in 1 blister pack / 3 in 1 carton NDC 82347-0030-4
112 mcg – 10 in 1 blister pack / 3 in 1 carton NDC 82347-0035-4

Source: FDA drug labeling via NLM DailyMed, data as of November 2, 2026. FDA data (DailyMed, Orange Book, Drug Shortages, enforcement reports). Not a substitute for the advice of a doctor or pharmacist.