What is Levothyroxine? Uses, warnings & side effects

Take your medicine as directed. Your dose may need to be changed several times to find what works best for you. 

Read and follow the patient instructions that come with this medicine. Talk to a doctor or pharmacist if you have any questions.

You may have to take this medicine for 4 to 8 weeks before your symptoms start to get better.

Take this medicine in the morning on an empty stomach, at least 30 to 60 minutes before eating breakfast.

If you take calcium supplements, calcium carbonate, iron supplements, or antacids, take levothyroxine at least four hours before or four hours after you take one of these supplements or antacids.

How to take levothyroxine tablets

• Swallow the levothyroxine tablet whole.

• If you are giving this medicine to a baby or child who cannot swallow the tablet whole, crush the tablet and mix it with 1 to 2 teaspoons of water and give the mixture to the child.

• Levothyroxine tablets normally need to be stored at room temperature and protected from light, heat, and moisture.

How to take levothyroxine capsules

• Swallow the levothyroxine capsule whole. Do not cut, crush, or chew the capsules.

• Store levothyroxine capsules at room temperature protected from light, moisture, and heat.

How to take levothyroxine oral solution

• This medicine will either come in a bottle or single-dose vials (Tirosint-Sol)

• Neither the bottle nor the vials need to be shaken before use.

• For levothyroxine oral solution vials, use one vial per day.

• The contents of the vial can be poured directly into the mouth, poured into a spoon, or mixed with a cup of water. 

• For levothyroxine oral solution bottles, measure each dose with the calibrated syringe that comes with the medicine. It’s very important to measure these doses precisely.

• Store levothyroxine oral solution at room temperature.

Take a dose as soon as you remember. If it is almost time for your next dose, wait until then and take a regular dose. 

Do not take extra medicine to make up for a missed dose.

This medicine is not right for everyone. 

Do not use it if you have an underactive adrenal gland (adrenal insufficiency) that hasn’t been corrected.

People who are allergic to any of the ingredients in the pills or oral solution (such as glycerol) should not take levothyroxine products with those ingredients. Switch to another version of levothyroxine.

Tell any doctor or other healthcare provider who treats you that you are using this medicine.

Your doctor may need to do lab tests regularly to check on the effects of this medicine and make sure the dose is correct. Keep all appointments.

Tell your doctor if you are pregnant or breastfeeding.

Tell your doctor if you have:

• Heart problems

• Thyroid nodules

• Kidney disease

• Pituitary gland problems

• Adrenal gland problems

• Diabetes

• Low red blood cell counts

• A history of blood clotting problems

• Food or drug allergies

Tell your doctor if you have recently received radiation treatment with iodine.

This medicine may cause the following problems:

• Heart problems, including angina (chest pain)

• Heart rhythm abnormalities

• Worsening of diabetes

• Bone weakening and loss of bone density

This medicine should never be used to treat obesity or as part of a treatment plan for a weight control program. It should never be used to enhance athletic performance.

Do not stop taking levothyroxine except under the advice of your doctor.

To avoid potentially hazardous drug interactions, tell the prescribing healthcare provider about all prescription drugs, over-the-counter medications, and supplements you use before taking amitriptyline.

Tell other healthcare providers you are using this medicine before they prescribe new medications.

Some medicines can affect how levothyroxine works or increase the risk or severity of side effects. Alternatively, levothyroxine can affect how other medicines work. Tell your doctor if you are taking:

• Birth control pills

• Diabetes medications or insulin

• Drugs that treat depression

• NSAIDs such as aspirin or ibuprofen

• Aspirin and drugs like aspirin called salicylates

• Steroids like testosterone or prednisone

• Blood pressure medications called beta blockers

• Cholesterol treatments called fibrates

• Blood thinners 

• The anticancer drugs mitotane, tamoxifen, asparaginase, or tyrosine-kinase inhibitors

• The heart rhythm drugs amiodarone or digoxin

• The anti-seizure drugs carbamazepine, phenytoin, or phenobarbital

• The diuretic furosemide

• Extended-release niacin

• Ketamine

• Heroin or methadone

Some drugs, foods, or supplements can affect how well the body absorbs your levothyroxine dose. These foods, supplements, and drugs can be taken with levothyroxine as long as they’re taken 4 hours before or 4 hours after the day’s levothyroxine dose:

• Soy products or soybean flour

• High-fiber foods

• Dietary supplements containing iron, calcium, or magnesium

• Antacids

• Heartburn or ulcer drugs called proton pump inhibitors

• The ulcer drug sucralfate

• High cholesterol drugs called bile acid sequestrants 

• The stomach gas drug simethicone

• The obesity treatment orlistat

• Treatments for high electrolyte levels including kayexalate, sevelamer, or lanthanum

Do not eat grapefruit or drink grapefruit juice while you are using this medicine.