Overview: Levothyroxine is used as a replacement hormone therapy for people with low thyroid hormone levels, among other uses. Levothyroxine interacts with many medicines and health conditions. Always make sure your health care provider knows all of your health conditions and medicines, including any over-the-counter (OTC) products. Levothyroxine comes in a liquid form for people that have a hard time swallowing tablets or capsules.

Uses

What is levothyroxine used for?

Levothyroxine is commonly used for the following.

Levothyroxine may also be used for other conditions as determined by your health care provider.

How does levothyroxine work (mechanism of action)?

Levothyroxine provides a source of thyroid hormone in people who may not make enough on their own. Levothyroxine may also be used for thyroid cancer. Taking it tells the thyroid gland to stop producing its own hormones, which can help stop the growth of thyroid cancer.

How is levothyroxine supplied (dosage forms)?

Brands and other names

  • Ermeza
  • Levo-T
  • Synthroid
  • Thyquidity
  • Tirosint
  • Tirosint-Sol

Dosage forms and strengths

  • 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg, 300 mcg oral tablets
  • 13 mcg, 25 mcg, 37.5 mcg, 50 mcg, 62.5 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg oral capsules
  • 13 mcg/mL, 20 mcg/mL, 25 mcg/mL, 30 mcg/mL, 37.5 mcg/mL, 44 mcg/mL, 50 mcg/mL, 62.5 mcg/mL, 75 mcg/mL, 88 mcg/mL, 100 mcg/mL, 112 mcg/mL, 125 mcg/mL, 137 mcg/mL, 150 mcg/mL, 175 mcg/mL, 200 mcg/mL oral liquid

How should I store levothyroxine?

Oral Tablets. Levothyroxine tablets should be stored at room temperature, between 68 F and 77 F (20 C and 25 C).  They can be exposed to temperatures between 59 F and 86 F (15 C and 30 C) for shorter periods of time, such as when transporting them. Protect tablets from light and moisture. 

Oral Capsules. Levothyroxine capsules should be stored at room temperature, between 68 F and 77 F (20 C and 25 C).  They can be exposed to temperatures between 59 F and 86 F (15 C and 30 C) for shorter periods of time, such as when transporting them. Protect capsules from heat, light, and moisture. 

Oral Liquid. Levothyroxine liquid should be stored at room temperature, between 68 F and 77 F (20 C and 25 C).  It can be exposed to temperatures between 59 F and 86 F (15 C and 30 C) for shorter periods of time, such as when transporting it. Protect the liquid from light. Follow all instructions about keeping the liquid in the container and about when you should throw any unused liquid away after opening the bottle or pouch. 

Side Effects

What are the most common side effects of levothyroxine?

The most common side effects of levothyroxine are listed below. Tell your health care provider if you have any of these side effects that bother you.

  • Arrhythmias, which are abnormal heart rhythms
  • Heart attack
  • Shortness of breath
  • Muscle spasms or weakness
  • Headache
  • Nervousness
  • Crankiness
  • Trouble sleeping
  • Tremors
  • Increased appetite
  • Weight loss
  • Diarrhea
  • Trouble tolerating heat
  • Menstrual changes
  • Skin rash

There may be other side effects of levothyroxine that are not listed here. Contact your health care provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088 (800-332-1088). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of levothyroxine?

While less common, the most serious side effects of levothyroxine are described below, along with what to do if they happen.

Severe Allergic Reactions. Levothyroxine may cause allergic reactions, which can be serious. Stop taking levothyroxine and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Trouble swallowing or throat tightness
  • Itching, skin rash, or pale red bumps on the skin called hives
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain

Heart Problems. Levothyroxine may cause your heart rate to increase or become abnormal. You may also have chest pain. Your risk may be higher if you are older, have heart problems, or if you take too much levothyroxine. Tell your health care provider right away if you notice any of the following.

  • Chest pain or pressure
  • Fast or abnormal heartbeat
  • Shortness of breath

Weak Bones. Levothyroxine may cause your bones to become weaker, leading to reduced bone density (osteopenia). It may also cause a more serious condition called osteoporosis, which can cause your bones to break (fracture) more easily. You may be at higher risk of this if you take too much levothyroxine or if you have gone through menopause. Tell your health care provider if you break a bone, and get a bone mineral density test if one is ordered for you.    

Warnings & Precautions

Who should not use levothyroxine?

Allergies to Ingredients. People who are allergic to any of the following should not take levothyroxine.

  • Levothyroxine
  • Ermeza
  • Levo-T
  • Synthroid
  • Thyquidity
  • Tirosint
  • Tirosint-Sol
  • Any of the ingredients in the specific product dispensed

Your pharmacist can tell you all of the ingredients in the specific levothyroxine products they stock.

Reduced Adrenal Function (Adrenal Insufficiency). You should not take levothyroxine If you have reduced adrenal function that is not being treated. 

What should I know about levothyroxine before using it?

Do not take levothyroxine unless it has been prescribed to you by a health care provider. Take it as prescribed. You should not use levothyroxine to lose weight or for obesity.

Do not share levothyroxine with other people, even if they have the same condition as you. It may harm them.

If you need to measure a dose of the levothyroxine liquid, use an accurate measuring device. A household spoon is not an accurate measuring device and may cause you to take the wrong dose. Ask your pharmacist to recommend a good measuring device. Some levothyroxine liquid may come in small individual containers that do not require any measuring. These containers should stay in the pouch until you are ready to take a dose. Follow any “Instructions for Use” that come with your liquid levothyroxine about mixing with water or other liquids. 

Do not open, chew, cut, or crush levothyroxine capsules. They should be swallowed whole. 

Keep levothyroxine out of the reach of children.

People who are elderly may be at greater risk of some side effects of levothyroxine. Talk to your health care provider about your risks if you are 65 years of age or older. 

You may notice hair loss while taking levothyroxine, especially when you first start taking it. This is rare, and the hair loss is usually temporary. 

Certain medicines can change how much levothyroxine gets into your blood. You may need to separate some medicines by about four hours before or after levothyroxine. Talk to your health care provider about all of the medicines you take. See the Drug Interactions section for more details.

It can take several weeks for the full effect of levothyroxine to be seen. Do not stop taking or change your dose of levothyroxine without talking to your health care provider. Levothyroxine is usually taken long-term.

What should I tell my health care provider before using levothyroxine?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if levothyroxine is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions. Tell your health care provider if you have any of the following. 

  • Any food allergies
  • Heart or blood vessel disease
  • Reduced adrenal function
  • Diabetes
  • Thyroid nodules
  • Myxedema coma
  • Low red blood cell levels (anemia)
  • Weak bones (osteoporosis)
  • Recently received radiation therapy with iodine
  • You are post-menopausal
  • Upcoming surgery or dental procedures
  • Pituitary problems
  • Clotting problems

Pregnancy. It is not known if or how levothyroxine could affect pregnancy or harm an unborn baby. Tell your health care provider if you are pregnant or plan to become pregnant. Your health care provider will let you know if you should take levothyroxine while you are pregnant or trying to get pregnant. If you continue taking levothyroxine during pregnancy, your health care provider may monitor your thyroid levels more often. 

Breastfeeding. Levothyroxine passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed. Your health care provider will let you know if you should take levothyroxine while breastfeeding.

Other Medicines and Supplements. Levothyroxine may interact with other medicines and supplements. Before taking levothyroxine, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Interactions

Does levothyroxine interact with foods or drinks?

It is important to take levothyroxine the same way each day. It should be taken on an empty stomach. Most levothyroxine products should be taken at least one-half to one hour before your first meal of the day. You may be able to take some liquid levothyroxine products as close as 15 minutes before eating. Follow any specific instructions given to you about separating levothyroxine from food. Ask your pharmacist if you have any questions about when to take your levothyroxine. 

Certain foods may affect the amount of levothyroxine that is absorbed into the body. Talk with your health care provider about how the following foods can affect your blood levels of levothyroxine. 

  • Soybean flour (infant formula)
  • Cottonseed meal
  • Walnuts
  • Dietary fiber
  • Grapefruit juice

It is unknown if drinking alcohol will affect levothyroxine.

Does levothyroxine interact with other medicines (drug interactions)?

Levothyroxine interacts with many other medicines. Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before taking levothyroxine.

  • Certain OTC vitamins/minerals such as calcium carbonate and ferrous sulfate
  • Orlistat, which is used for weight loss
  • Slow-release nicotinic acid or a bile acid sequestrant, such as cholestyramine (Prevalite), colestipol (Colestid), or colesevelam (Welchol), which is a medicine to lower cholesterol
  • Kayexalate, which is a medicine used to treat high potassium in the blood
  • Sevelamer, which is a medicine used to treat high phosphate in the blood
  • An antacid, sucralfate, or a proton pump inhibitor (PPI), such as esomeprazole (Nexium), lansoprazole (Prevacid), omeprazole (Prilosec), pantoprazole (Protonix), or rabeprazole (Aciphex), which is used for stomach acid problems
  • A hormone, such as estrogen (in birth control pills and hormone replacement therapy) or testosterone
  • Methadone, which is an opioid medicine used to treat pain or opioid use disorder
  • 5-fluorouracil (5-FU), asparaginase, mitotane, tamoxifen, and certain medicines known as tyrosine-kinase inhibitors, which are chemotherapy agents that are used to treat or prevent certain cancers
  • A corticosteroid, such as dexamethasone, methylprednisolone, or prednisone, which is a medicine for certain inflammatory conditions
  • A corticosteroid, which is a medicine for certain inflammatory conditions
  • A salicylate, such as diflunisal or salsalate, which is a medicine used for osteoarthritis or rheumatoid arthritis
  • Any medicine for seizures, such as carbamazepine, phenobarbital, or phenytoin 
  • A nonsteroidal anti-inflammatory drug (NSAID), such as ibuprofen, naproxen, and others, which are contained in many prescription and OTC products for pain, swelling, and fever
  • Rifampin, which is a medicine used to treat certain infections
  • Amiodarone, propranolol, or digoxin, which is a medicine used for certain heart conditions
  • A medicine for diabetes
  • A blood thinner, which is a medicine used to treat or prevent blood clots
  • A tricyclic antidepressant or maprotiline, even if it is not used for depression
  • A weight loss medication, such as diethylpropion, phendimetrazine, or phentermine (Adipex-P, Lomaira, Qsymia) 

Some other medicines may alter the blood levels of levothyroxine. Tell your health care provider about all medicines that you take or have recently taken.

This may not be a complete list of medicines that can interact with levothyroxine. Always check with your health care provider.

Does interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much levothyroxine?

If you or someone else has used too much levothyroxine, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of levothyroxine?

If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and only take the next dose. Do not take double or extra doses.