Synthroid (Levothyroxine Oral)

Generic name: Levothyroxine
Drug class: Thyroid drugs

Usage of Synthroid (Levothyroxine Oral)

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.

This medicine is available only with your doctor's prescription.

Synthroid (Levothyroxine Oral) 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, discomfort, or tightness
  • 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
  • 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:

    Less common

  • Change in appetite
  • crying
  • diarrhea
  • false or unusual sense of well-being
  • fear or nervousness
  • feeling not well or unhappy
  • feeling of discomfort
  • feeling of warmth
  • feeling things are not real
  • feelings of suspicion and distrust
  • hair loss
  • headache
  • increased appetite
  • mental depression
  • muscle weakness
  • quick to react or overreact emotionally
  • rapidly changing moods
  • redness of the face, neck, arms, and occasionally, upper chest
  • restlessness
  • stomach cramps
  • trouble getting pregnant
  • trouble sitting still
  • unusual tiredness or weakness
  • vomiting
  • weight gain or loss

    • Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

    Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

    Before taking Synthroid (Levothyroxine Oral)

    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 this medicine, the following should be considered:

    Allergies

    Tell your doctor if you have ever had any unusual or allergic reaction to this medicine 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. However, your child's doctor will check your child closely for heart problems during the first 2 weeks of treatment.

    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.

    Breast Feeding

    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 this medicine, 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 this medicine 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.

  • Furosemide
  • Iopromide
  • Midodrine

    • Using this medicine 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
  • 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 this medicine 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 this medicine, or give you special instructions about the use of food, alcohol, or tobacco.

  • Enteral Nutrition
  • Soybean

    • Other Medical Problems

    The presence of other medical problems may affect the use of this medicine. Make sure you tell your doctor if you have any other medical problems, especially:

  • Adrenal gland insufficiency (underactive adrenal gland), untreated or
  • Heart attack, acute or recent or
  • Thyrotoxicosis (overactive thyroid), untreated—Should not be used in patients with these conditions.
  • Adrenal gland problems or
  • Anemia, pernicious or
  • Angina (severe chest pain), history of or
  • Blood clotting problems, or history of or
  • Diabetes or
  • Heart or blood vessel disease (eg, coronary artery disease, heart failure), history of or
  • Heart rhythm problems (eg, arrhythmia, atrial fibrillation), history of or
  • Osteoporosis, history of—Use with caution. May make these conditions worse.
  • Hypoproteinemia (low levels of protein in the blood), severe or
  • Kidney disease (eg, nephrosis) or
  • Liver disease (eg, hepatitis), severe or
  • Pituitary gland problems (eg, acromegaly) or
  • Porphyria (enzyme problem)—Use with caution. May need to adjust the dose of levothyroxine in patients with these conditions.
  • Patients who have trouble swallowing capsules (including children younger than 6 years of age)—Tirosint® should not be given in these patients.

    • Relate drugs

    How to use Synthroid (Levothyroxine Oral)

    This medicine will need to be taken for the rest of your life or your child's life. Do not stop taking this medicine or change your dose without first checking with your doctor. 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.

    Swallow the capsule whole. Do not cut, chew, or crush it.

    If your child is unable to swallow the tablet, you may crush and mix it in 1 to 2 teaspoons (5 to 10 milliliters) of water. Give the mixture right away using a spoon or dropper. Do not mix the tablet with any other liquid except water. Do not store the mixture for future use.

    If you are using the oral liquid:

  • This medicine 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 this medicine 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.

    • If you are using kayexalate, lanthanum, orlistat, sevelamer, sucralfate, antacids (eg, aluminum or magnesium hydroxide, simethicone, Maalox®, Mylanta®, Tums®), medicine to lower cholesterol (eg, cholestyramine, colesevelam, colestipol, Prevalite®,Welchol®, Colestid®), stomach medicine (eg, lansoprazole, omeprazole, pantoprazole, Aciphex®, Dexilant®, Nexium®, Prevacid®, Prilosec®), or any medicine that contains calcium or iron, take them at least 4 hours before or 4 hours after you take levothyroxine.

    Cotton seed meal, dietary fiber, soybean flour (infant formula), or walnuts may decrease the absorption of this medicine from your body. You may have to take this medicine 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 this medicine.

    Dosing

    The dose of this medicine 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 this medicine. 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. Your doctor may adjust your dose as needed or tolerated.
  • 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. Your doctor may adjust your dose as needed or tolerated.
  • 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. Your doctor may adjust your dose as needed or tolerated.
  • 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. Your doctor may adjust your dose as needed or tolerated.
  • 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. Your doctor may adjust your dose as needed or tolerated.
  • 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. Your doctor may adjust your dose as needed or tolerated.
  • 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. Your doctor may adjust your dose as needed or tolerated.

    • Missed Dose

    If you miss a dose of this medicine, 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.

    Warnings

    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. This medicine 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 this medicine, 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 this medicine 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 has 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.

    This medicine may cause severe hypothyroidism, called myxedema coma, which may be life-threatening and requires immediate medical attention. Check with your doctor right away if you have weakness, confusion or non-responsiveness, feeling cold, low body temperature, swelling of the body, especially the face, tongue, and lower legs, or difficulty breathing.

    Do not suddenly stop taking this medicine 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 this medicine. You or your child may need to stop using this medicine 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.

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