SYNTHROID® (levothyroxine sodium tablets, USP) contain synthetic crystalline L-3,3′,5,5′-tetraiodothyronine sodium salt [levothyroxine (T₄) sodium]. Synthetic T₄ is identical to that produced in the human thyroid gland. Levothyroxine (T₄) sodium has an empirical formula of C15H10I4N NaO4•H2O, molecular weight of 798.86 g/mol (anhydrous), and structural formula as shown:Inactive Ingredients: acacia, confectioner’s sugar (contains corn starch), lactose monohydrate, magnesium stearate, povidone, and talc.
Common uses
This medicine is a thyroid hormone used to treat hypothyroidism. It may also be used to treat other conditions as determined by your doctor.
Before using
Warning: this medicine should not be used either alone or in combination with diet pills to treat obesity or for weight loss because serious, even life-threatening, effects could occur. Large doses of this medicine, especially with diet pills, may cause symptoms of toxicity. (see possible side effects and overdose sections for more information). Some medicines or medical conditions may interact with this medicine.Additional monitoring of your dose or condition may be needed if you are taking warfarin, digoxin, estrogen products (including estrogen-containing birth control pills), diabetes medicines (e.g., insulin, glipizide, rosiglitazone), amiodarone, iodide (including radiographic contrast agents containing iodine), lithium, anti-thyroid agents (e.g., methimazole, propylthiouracil), androgens or anabolic steroids, glucocorticoids (e.g., dexamethasone, prednisone), high dose salicylates (e.g., aspirin), phenobarbital, rifamycins (e.g., rifampin), beta-blockers (e.g., propranolol), antidepressants (e.g., amitriptyline, maprotiline, sertraline), cytokines (e.g., interferon-alpha, interleukin-2), growth hormones, ketamine, theophylline.Inform your doctor of any other medical conditions including heart problems (e.g., hypertension, congestive heart failure, arrhythmias, coronary artery disease), diabetes, male or female infertility problems, bone loss (osteoporosis), other hormone disorders, other thyroid problems, blood clotting disorders, allergies, pregnancy, or breast-feeding.Use of this medicine is not recommended if you have a history of overactive thyroid condition (e.g., thyrotoxicosis), a heart attack (acute myocardial infarction), or adrenal gland problems (e.g., uncorrected adrenal insufficiency).
Directions
Take this medicine on an empty stomach at least 1 hour before or 2 to 3 hours after eating. It is recommended that you take your dose 1 hour before breakfast unless otherwise directed by your doctor.Try to take this medicine at the same time each day. This medicine works best when there is a constant level of the drug in your body. For children who cannot swallow whole tablets, crush the tablet and mix in 1 or 2 teaspoons (5 or 10 ml) of water, and give using a spoon or dropper as soon as possible after preparation. Do not store the mixture for later use. Do not mix crushed tablets in soybean infant formula.Some medicines may decrease the absorption of this medicine into your bloodstream. Therefore, take this medicine 4 hours apart from calcium supplements, iron, antacids (those containing aluminum, calcium, or magnesium), simethicone, cholestyramine, colestipol, sucralfate, or sodium polystyrene sulfonate.Store this medicine at room temperature in a tightly-closed container, away from heat, moisture, and light. If you miss a dose of this medicine, take it as soon as possible. If it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not take 2 doses at once.
Cautions
Continuous use of this medicine for a few weeks may be necessary to relieve symptoms of your condition. Symptoms of low thyroid hormone levels include fatigue, muscle aches, constipation, dry skin, weight gain, slow heart rate, sensitivity to cold, or dry brittle hair that tends to fall out easily. These symptoms should disappear as your body adjusts to the medicine. If they persist or become bothersome, notify your doctor promptly as your dose may need to be adjusted. Do not adjust your dose or stop taking this medicine without checking with your doctor.Tell the doctor or dentist that you are taking this medicine before you have emergency treatment or surgery. Keep all doctor and laboratory appointments (e.g., thyroid function tests) while you are taking this medicine. Before you begin taking any new medicine, either prescription or over-the-counter, check with your doctor or pharmacist. This includes calcium or aluminum-containing antacids, iron preparations and cough-and-cold products, or diet aids.Caution is advised when using this medicine in the elderly because they may be more sensitive to the effects of this medicine. Caution is advised when using this medicine in children because overuse may reduce the child’s final adult height. For women: inform your doctor if you become pregnant, as your dose may need to be adjusted. This medicine is excreted in breast milk. Consult your doctor before breast-feeding.
Possible side effects
Side effects that may occur while taking this medicine include headache, nervousness, trembling, sweating, increased appetite, diarrhea, weight loss or insomnia. If they continue or are bothersome, check with your doctor as your dose may need to be adjusted. In rare instances, some hair loss may occur during the first few months of starting this medicine. This effect is usually temporary as your body adjusts to this medicine. If this effect persists or worsens, notify your doctor as soon as possible.Contact your doctor immediately if you experience chest pain, rapid or irregular heartbeat, shortness of breath, or seizures. An allergic reaction to this medicine is unlikely, but if you experience difficulty breathing; tightness of chest; swelling of eyelids, face, or lips; or if you develop a rash or hives, tell your doctor immediately. If you notice other effects not listed above, contact your doctor or pharmacist.
If you take too much
If overdose is suspected, contact your local poison control center or emergency room immediately. Symptoms of overdose may include excessive sweating, extreme nervousness, irregular heartbeat, chest pain, or seizures.
Additional information
Do not share this medicine with others for whom it was not prescribed. Do not use this medicine for other health conditions. Keep this medicine out of the reach of children and pets. If using this medicine for an extended period of time, obtain refills before your supply runs out.
Drug interactions
Drug interactions can result in unwanted side effects or prevent a medicine from doing its job. Some medicines or medical conditions may interact with this medicine. Inform your doctor or pharmacist of all prescription and over-the-counter medicine that you are taking.