Levothyroxine (By mouth)


Levothyroxine (lee-voe-thye-ROX-een)
Treats hypothyroidism, which is when your body does not produce enough thyroid hormone. Also used to treat an enlarged thyroid gland (goiter) and thyroid cancer.

Brand Name(s)

There may be other brand names for this medicine.

Synthroid, Levoxyl, Levothroid, Unithroid, Tirosint

When This Medicine Should Not Be Used

You should not use this medicine if you have had an allergic reaction to any type of thyroid hormone or to a color dye. You should not use this medicine if you have high levels of thyroid hormone in your blood (hyperthyroidism) or if you have recently had a heart attack. This medicine should not be used to treat obesity or for weight loss.

How to Use This Medicine

Capsule, Tablet
  • Your doctor will tell you how much of this medicine to use and how often. Your dose may need to be changed several times in order to find out what works best for you. Do not use more medicine or use it more often than your doctor tells you to.
  • Use only the brand of this medicine that your doctor prescribed. Different brands may not work the same way.
  • Take this medicine in the morning on an empty stomach. Wait at least a half hour (30 minutes) before you eat any food.
  • Swallow this tablet with a full glass (8 ounces) of water. This will help prevent choking or gagging on the tablet. If you still have trouble swallowing the tablet, talk to your doctor or pharmacist.
  • If this medicine is being given to a baby or a small child, you can crush the tablet and mix it in a small amount (1 to 2 teaspoons) of water. This mixture can be given by spoon or dropper. Do not mix the tablet with any other liquid except water, unless your doctor says it is okay. Do not store the mixture. If you do not give the medicine right after it is mixed, throw the medicine away.
  • Some people must take this medicine every day for the rest of their life.
If a dose is missed:
  • If you miss a dose or forget to use your medicine, use it as soon as you can. If it is almost time for your next dose, wait until then to use the medicine and skip the missed dose. Do not use extra medicine to make up for a missed dose.

How to Store and Dispose of This Medicine

  • Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light.
  • Ask your pharmacist, doctor, or health caregiver about the best way to dispose of any leftover medicine after you have finished your treatment. You will also need to throw away old medicine after the expiration date has passed.
  • Keep all medicine away from children and never share your medicine with anyone.

Drugs and Foods to Avoid

Ask your doctor or pharmacist before using any other medicine, including over-the-counter medicines, vitamins, and herbal products.
  • There are many other medicines that you should not use together with levothyroxine. This includes nonprescription (over-the-counter) medicines. Make sure your doctor knows about all other medicines you are using.
  • Make sure your doctor knows if you are using digoxin (Lanoxin®), a blood thinner (such as heparin, warfarin, Coumadin®) or a diabetes medicine (such as glipizide, glyburide, metformin, repaglinide, tolbutamide, Actos®, Glucotrol®, Prandin®).
  • Tell your doctor if you are using rifampin, medicines to treat heart problems (such as amiodarone, furosemide, propranolol, Diuril®, Inderal®, Lasix®), medicines to treat epilepsy or seizures (such as carbamazepine, diazepam, phenobarbital, phenytoin, Luminal®, Tegretol®), or pain or arthritis medicines, also called "NSAIDs" (such as aspirin, mefenamic acid, phenylbutazone, Ponstel®).
  • Make sure your doctor knows if you are also using medicines to treat depression (such as amitriptyline, doxepin, imipramine, maprotiline, nortriptyline, sertraline, Elavil®, Ludiomil®, Pamelor®, Sinequan®, Zoloft®), medicines to treat Parkinson's disease (such as bromocriptine, ropinirole, Parlodel®, Requip®), medicines to treat thyroid problems (such as methimazole, PTU, Tapazole®), or growth hormones (such as octreotide, somatrem, somatropin, Sandostatin®, Nutropin®).
  • Tell your doctor if you are also using aminoglutethimide, iodide, heroin, ketamine, methadone, mitotane, tamoxifen (Nolvadex®), or theophylline (Theo-Dur®).
  • Make sure your doctor knows if you are also using any estrogens, or if you are using birth control pills that contain estrogen (such as estradiol, estropipate, Activella®, Climara®, Femhrt®, Premarin®, Vivelle-Dot®).
  • If you are using antacids (such as Amphojel®, Maalox®, Mylanta®, Tums®), medicines to treat high cholesterol (such as cholestyramine, colestipol, Colestid®, Questran®), orlistat (Xenical®), sucralfate (Carafate®), or any medicine that contains calcium or iron, take it at least 4 hours before or 4 hours after you take levothyroxine.
  • Do not eat a cotton seed meal, dietary fiber, soybean flour (infant formula), or walnuts when you take this medicine.

Warnings While Using This Medicine

  • Make sure your doctor knows if you are pregnant or breastfeeding, or if you plan to become pregnant. Your doctor should also know if you are postmenopausal or if you have osteoporosis (bone loss).
  • Tell your doctor if you have heart disease, blood clots, or diabetes. Make sure your doctor knows if you have pituitary gland problems, or adrenal gland problems such as Addison's disease.
  • Tell your doctor if you have problems with your blood, such as anemia, or if you are allergic to any foods or medicines.
  • You may have to take this medicine for 6 to 8 weeks before your symptoms start to get better.
  • Do not stop using this medicine suddenly without asking your doctor. You may need to slowly decrease your dose before stopping it completely.
  • Make sure any doctor or dentist who treats you knows that you are using this medicine. You may need to stop using this medicine several days before having surgery or medical tests.
  • Your doctor will need to check your blood at regular visits while you are using this medicine. Be sure to keep all appointments.

Possible Side Effects While Using This Medicine

Call your doctor right away if you notice any of these side effects:
  • Allergic reaction: Itching or hives, swelling in your face or hands, swelling or tingling in your mouth or throat, chest tightness, trouble breathing.
  • Chest pain, fast, uneven or pounding heartbeat.
  • Confusion, anxiety, or disorientation.
  • Fever, heat intolerance, sweating, hunger, tired feeling, or weight loss.
  • Severe irritability, nervousness, or tremors.
  • Severe vomiting, diarrhea, or stomach pain.
  • Shortness of breath, cold sweats, and bluish-colored skin.
  • Swelling in your hands, ankles, or feet.
If you notice these less serious side effects, talk with your doctor:
  • Changes in your menstrual periods.
  • Hair loss.
  • Headache.
  • Leg cramps.
  • Trouble sleeping.

If you notice other side effects that you think are caused by this medicine, tell your doctor

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088
Review Date: 2011-02-04 Reviewed By: Keywords: ,
Adam Data Copyright The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only--they do not constitute endorsements of those other sites. © 1997- 2010 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.

For information 410.787.4000

© 2015 UM Baltimore Washington Medical Center.  All rights reserved.

301 Hospital Drive, Glen Burnie, MD 21061 | 410-787-4000 | TTY 410-787-4498