Levothyroxine

Uses for levothyroxine

Levothyroxine is used to treat hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormone. Levothyroxine is also used to help decrease the size of enlarged thyroid glands (also called a goiter) and to treat thyroid cancer.

Levothyroxine is available only with your doctor's prescription.

Before using levothyroxine

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For levothyroxine, the following should be considered:

Allergies

Tell your doctor if you have ever had any unusual or allergic reaction to levothyroxine or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.

Pediatric

Appropriate studies performed to date have not demonstrated pediatric-specific problems that would limit the usefulness of levothyroxine in children.

Geriatric

Appropriate studies performed to date have not demonstrated geriatric-specific problems that would limit the usefulness of levothyroxine in the elderly. However, elderly patients are more likely to have age-related heart or blood vessel problems, which may require caution and an adjustment in the dose for patients receiving levothyroxine.

Breastfeeding

Studies in women suggest that this medication poses minimal risk to the infant when used during breastfeeding.

Interactions with medicines

Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking levothyroxine, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Using levothyroxine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

Midodrine

Using levothyroxine with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

Aluminum Carbonate, Basic
Aluminum Hydroxide
Aluminum Phosphate
Calcium Acetate
Calcium Carbonate
Calcium Citrate
Chlorotrianisene
Cholestyramine
Chromium
Ciprofloxacin
Colesevelam
Conjugated Estrogens
Conjugated Estrogens Synthetic A
Conjugated Estrogens Synthetic B
Dexlansoprazole
Dienestrol
Diethylstilbestrol
Dihydroxyaluminum Aminoacetate
Dihydroxyaluminum Sodium Carbonate
Eltrombopag
Esomeprazole
Esterified Estrogens
Estradiol
Estramustine
Estriol
Estropipate
Ethinyl Estradiol
Fosphenytoin
Imatinib
Iron
Kelp
Lansoprazole
Lanthanum Carbonate
Lopinavir
Magaldrate
Magnesium Carbonate
Magnesium Hydroxide
Magnesium Oxide
Magnesium Trisilicate
Mestranol
Omeprazole
Pantoprazole
Patiromer
Phenytoin
Polyestradiol Phosphate
Promestriene
Quinestrol
Rabeprazole
Rifampin
Ritonavir
Semaglutide
Sevelamer
Simvastatin
Tibolone

Interactions with food/tobacco/alcohol

Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Using levothyroxine with any of the following may cause an increased risk of certain side effects but may be unavoidable in some cases. If used together, your doctor may change the dose or how often you use levothyroxine, or give you special instructions about the use of food, alcohol, or tobacco.

Enteral Nutrition
Soybean

Proper use of levothyroxine

Levothyroxine will need to be taken for the rest of your life or your child's life. Do not stop taking levothyroxine or change your dose without first checking with your doctor. It may take several weeks before you start to notice that your symptoms are better.

It is best to take levothyroxine on an empty stomach. Take it with a full glass of water at least 30 minutes to 1 hour before eating breakfast.

Swallow the capsule whole. Do not cut or crush it. Also, if you are taking multiple strengths of levothyroxine, remove the capsules from the blisters in advance to help you identify the strength of each capsule.

For infants and children who cannot swallow the tablet form, the tablet can be crushed and mixed with a small amount of water (5 to 10 milliliters [mL] or 1 to 2 teaspoonfuls). You may use a spoon or dropper to give the mixture. Use the mixture right away and do not store it to use later.

If you are using the oral liquid:

Levothyroxine should come with patient instructions. Read and follow the instructions carefully. Ask your doctor if you have any questions.
Levothyroxine may be mixed with water or be given directly into the mouth.
If mixed with water, squeeze the contents of 1 single unit-dose ampule into a glass or cup containing water. Stir and drink it immediately. Add some water to the glass or cup and drink the water. This will help get all of the medicine out of the glass or cup. Do not mix levothyroxine with any other liquid except water. Do not store the mixture for later use.
If taken without water, squeeze the medicine directly into the mouth or into a spoon and swallow it immediately.

Levothyroxine should be taken at least 4 hours before or 4 hours after these medicines: antacids (Maalox®, Mylanta®, Tums®), calcium supplements, stomach medicines (including lansoprazole, omeprazole, pantoprazole, Aciphex®, Dexilant®, Nexium®, Prevacid®, Prilosec®), cholestyramine (Prevalite®, Questran®), colesevelam (Welchol®), colestipol (Colestid®), iron supplements, Kayexalate®, orlistat (Alli®, Xenical®), simethicone (Gas-X®, Mylicon®), and sucralfate (Carafate®).

Cotton seed meal, dietary fiber, soybean flour (infant formula), or walnuts may affect the absorption of levothyroxine from your body. You may have to take levothyroxine at a different time of day from when you eat these foods. Talk with your doctor more about this if you have concerns.

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

Dosing

The dose of levothyroxine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of levothyroxine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

For oral dosage form (capsules):
For hypothyroidism:
Adults and children older than 12 years of age (growth and puberty complete)—Dose is based on body weight and must be determined by your doctor. The dose is usually 1.7 microgram (mcg) per kilogram (kg) of body weight per day but may be less in older adults.
Children older than 12 years of age (growth and puberty incomplete)—Dose is based on body weight and must be determined by your doctor. The dose is usually 2 to 3 mcg per kg of body weight per day.
Children 6 to 12 years of age—Dose is based on body weight and must be determined by your doctor. The dose is usually 4 to 5 mcg per kg of body weight per day.
Children younger than 6 years of age—Use is not recommended as your child might not be able to swallow the capsules.
For thyroid cancer:
Adults—Dose is based on body weight and must be determined by your doctor. The dose is usually more than 2 microgram (mcg) per kilogram (kg) of body weight per day.
Children—Use and dose must be determined by your doctor.
For oral dosage form (solution):
For hypothyroidism:
Adults and children older than 12 years of age (growth and puberty complete)—Dose is based on body weight and must be determined by your doctor. The starting dose is usually 1.7 microgram (mcg) per kilogram (kg) of body weight per day. Your doctor may adjust your dose as needed.
Children older than 12 years of age (growth and puberty incomplete)—Dose is based on body weight and must be determined by your doctor. The dose is usually 2 to 3 mcg per kg of body weight per day.
Children 6 to 12 years of age—Dose is based on body weight and must be determined by your doctor. The dose is usually 4 to 5 mcg per kg of body weight per day.
Children 1 to 5 years of age—Dose is based on body weight and must be determined by your doctor. The dose is usually 5 to 6 mcg per kg of body weight per day.
Children 6 to 12 months of age—Dose is based on body weight and must be determined by your doctor. The dose is usually 6 to 8 mcg per kg of body weight per day.
Children 3 to 6 months of age—Dose is based on body weight and must be determined by your doctor. The dose is usually 8 to 10 mcg per kg of body weight per day.
Children 0 to 3 months of age—Dose is based on body weight and must be determined by your doctor. The dose is usually 10 to 15 mcg per kg of body weight per day.
For thyroid cancer:
Adults—Dose is based on body weight and must be determined by your doctor. The dose is usually more than 2 microgram (mcg) per kilogram (kg) of body weight per day.
Children—Use and dose must be determined by your doctor.
For oral dosage form (tablet):
For hypothyroidism:
Adults and children older than 12 years of age (growth and puberty complete)—Dose is based on body weight and must be determined by your doctor. The dose is usually 1.6 microgram (mcg) per kilogram (kg) of body weight per day but may be less in older adults.
Children older than 12 years of age (growth and puberty incomplete)—Dose is based on body weight and must be determined by your doctor. The dose is usually 2 to 3 mcg per kg of body weight per day.
Children 6 to 12 years of age—Dose is based on body weight and must be determined by your doctor. The dose is usually 4 to 5 mcg per kg of body weight per day.
Children 1 to 5 years of age—Dose is based on body weight and must be determined by your doctor. The dose is usually 5 to 6 mcg per kg of body weight per day.
Children 6 to 12 months of age—Dose is based on body weight and must be determined by your doctor. The dose is usually 6 to 8 mcg per kg of body weight per day.
Children 3 to 6 months of age—Dose is based on body weight and must be determined by your doctor. The dose is usually 8 to 10 mcg per kg of body weight per day.
Children 0 to 3 months of age—Dose is based on body weight and must be determined by your doctor. The dose is usually 10 to 15 mcg per kg of body weight per day.

Missed dose

If you miss a dose of levothyroxine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage

Keep out of the reach of children.

Do not keep outdated medicine or medicine no longer needed.

Ask your healthcare professional how you should dispose of any medicine you do not use.

Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.

Use the oral liquid within 15 days after opening the pouch. Keep the ampules in the pouch until you are ready to use them.

Detailed Levothyroxine dosage information

Precautions while using levothyroxine

If you will be taking levothyroxine for a long time, it is very important that your doctor check the progress of you or your child at regular visits. This will allow your doctor to see if the medicine is working properly and to decide if you should continue to take it. Blood tests will be needed to check for unwanted effects.

Levothyroxine should not be used for the treatment of obesity or for the purpose of losing weight. Levothyroxine is not effective for weight reduction. If taken in large amounts, levothyroxine may cause serious unwanted effects.

Hypothyroidism can sometimes cause infertility in men and women. Levothyroxine should not be used for the treatment of infertility unless it is caused by hypothyroidism.

For patients with diabetes: It is very important that you keep track of your blood or urine sugar levels as instructed by your doctor. Check with your doctor right away if you notice any changes in your sugar levels.

If you think you have become pregnant while using levothyroxine, tell your doctor right away. You may need a larger dose of levothyroxine while you are pregnant.

Women who are post-menopausal or who use levothyroxine for a long time may have some bone loss, which could lead to osteoporosis. Talk with your doctor if you have questions or concerns about this.

Call your doctor right away if you or your child start to have rapid or irregular heartbeats, chest pain, leg cramps, headaches, nervousness, irritability, sleeplessness, tremors, a change in appetite, weight gain or loss, vomiting, diarrhea, excessive sweating, heat intolerance, a fever, changes in menstrual periods, hives, or a skin rash. These could be symptoms of too much medicine in your body.

Do not suddenly stop taking levothyroxine without first checking with your doctor. Your doctor may want you or your child to gradually reduce the amount you are using before stopping completely.

Make sure any doctor or dentist who treats you knows that you or your child are using levothyroxine. You or your child may need to stop using levothyroxine several days before having surgery or medical tests.

A temporary loss of hair may occur during the first few months of levothyroxine therapy. Ask your doctor about this if you have any concerns.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.

Levothyroxine side effects

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur:

Less common

Chest pain or discomfort
decreased urine output
difficult or labored breathing
difficulty with swallowing
dilated neck veins
extreme fatigue
fainting
fast, slow, irregular, pounding, or racing heartbeat or pulse
fever
heat intolerance
hives or welts, skin itching, rash, or redness
irregular breathing
irritability
menstrual changes
nausea
pain or discomfort in the arms, jaw, back, or neck
sweating
swelling of the eyes, face, lips, throat, or tongue
tightness in the chest
tremors

Rare

Blurred or double vision
dizziness
eye pain
lack or slowing of normal growth in children
limp or walk favoring one leg
pain in the hip or knee
seizures
severe headache

Get emergency help immediately if any of the following symptoms of overdose occur:

Symptoms of overdose

Change in consciousness
cold, clammy skin
confusion
disorientation
fast or weak pulse
lightheadedness
loss of consciousness
sudden headache
sudden loss of coordination
sudden slurring of speech

Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them: