Generic Name: levothyroxine (Oral route)
Thyroid hormones, including levothyroxine, should not be used either alone or with other therapeutic agents for the treatment of obesity or weight loss. In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction. Larger doses may produce serious or even life-threatening manifestations of toxicity, particularly when given in association with sympathomimetic amines such as those used for their anorectic effects .
Commonly used brand name(s)
In the U.S.
Available Dosage Forms:
- Capsule, Liquid Filled
Therapeutic Class: Thyroid Supplement
Uses For Synthroid
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.
Before Using Synthroid
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:
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.
Appropriate studies performed to date have not demonstrated pediatric-specific problems that would limit the usefulness of levothyroxine in children.
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.
|All Trimesters||A||Adequate studies in pregnant women have not shown an increased risk of fetal abnormalities.|
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 not recommended. Your doctor may decide not to treat you with this medication or change some of the other medicines you take.
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.
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
- Conjugated Estrogens
- Dihydroxyaluminum Aminoacetate
- Dihydroxyaluminum Sodium Carbonate
- Esterified Estrogens
- Lanthanum Carbonate
- Magnesium Carbonate
- Magnesium Hydroxide
- Magnesium Oxide
- Magnesium Trisilicate
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
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 problems or
- Anemia, pernicious or
- Angina (severe chest pain), history of or
- Blood clotting problems or
- Diabetes or
- Heart or blood vessel disease (e.g., coronary artery disease), history of or
- Heart rhythm problems (e.g., arrhythmia, atrial fibrillation), history of or
- Osteoporosis, history of or
- Pituitary gland problems—Use with caution. May make these conditions worse.
- Patients who have trouble swallowing capsules (including children younger than 6 years of age)—Tirosint® should not be given in these patients.
Proper Use of levothyroxine
This section provides information on the proper use of a number of products that contain levothyroxine. It may not be specific to Synthroid. Please read with care.
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. It may take several weeks before you start to notice that your symptoms are better.
It is best to take this medicine on an empty stomach. Take it with a full glass of water at least 30 minutes to 1 hour before eating breakfast.
This medicine should be taken at least 4 hours before or 4 hours after these medicines: antacids (Maalox®, Mylanta®, Tums®), calcium supplements, cholestyramine (Prevalite®, Questran®), colestipol (Colestid®), iron supplements, orlistat (Alli®, Xenical®), simethicone (Gas-X®, Mylicon®), and sucralfate (Carafate®).
Swallow the capsule whole. Do not cut or crush it. Also, if you are taking multiple strengths of this medicine, 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.
Cotton seed meal, dietary fiber, soybean flour (infant formula), or walnuts may affect 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.
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 (tablet):
- For hypothyroidism:
- Adults and teenagers—Dose is based on body weight and must be determined by your doctor. The usual dose is 1.7 microgram (mcg) per kilogram (kg) per day but may be less in older adults.
- Children older than 12 years of age—Dose is based on body weight and must be determined by your doctor. The usual dose is 2 to 3 mcg per kg per day.
- Children 6 to 12 years of age—Dose is based on body weight and must be determined by your doctor. The usual dose is 4 to 5 mcg per kg per day.
- Children 1 to 5 years of age—Dose is based on body weight and must be determined by your doctor. The usual dose is 5 to 6 mcg per kg per day.
- Children 6 to 12 months of age—Dose is based on body weight and must be determined by your doctor. The usual dose is 6 to 8 mcg per kg per day.
- Children 3 to 6 months of age—Dose is based on body weight and must be determined by your doctor. The usual dose is 8 to 10 mcg per kg per day.
- Children 0 to 3 months of age—Dose is based on body weight and must be determined by your doctor. The usual dose is 10 to 15 mcg per kg per day.
- For hypothyroidism:
- For oral dosage form (capsules):
- For hypothyroidism:
- Children older than 12 years of age (but growth and puberty incomplete)—Dose is based on body weight and must be determined by your doctor. The usual dose is 2 to 3 mcg per kg 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 usual dose is more than 2 microgram (mcg) per kilogram (kg) per day.
- Children—Use and dose must be determined by your doctor.
- For hypothyroidism:
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.
Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.
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.
Precautions While Using Synthroid
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 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 start to have rapid or irregular heartbeats, chest pain, shortness of breath, 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 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.
Synthroid 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
- fast, slow, irregular, pounding, or racing heartbeat or pulse
- heat intolerance
- hives or welts
- increased blood pressure
- increased pulse
- irregular breathing
- menstrual changes
- pain or discomfort in the arms, jaw, back, or neck
- shortness of breath
- skin itching, rash, or redness
- swelling of the eyes, face, lips, throat, or tongue
- tightness in the chest
- troubled breathing
- Blurred or double vision
- eye pain
- lack or slowing of normal growth in children
- limp or walk favoring one leg
- pain in the hip or knee
- severe headache
Get emergency help immediately if any of the following symptoms of overdose occur:Symptoms of overdose
- Change in consciousness
- cold, clammy skin
- fast or weak pulse
- 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
- Abdominal or stomach cramps
- change in appetite
- false or unusual sense of well-being
- feeling not well or unhappy
- feeling of discomfort
- feeling of warmth
- feeling things are not real
- feelings of suspicion and distrust
- hair loss
- 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
- trouble getting pregnant
- trouble sitting still
- unusual tiredness or weakness
- weight gain
- weight 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.
See also: Side effects (in more detail)
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