Levothyroxine is a replacement for a hormone that is normally produced by your thyroid gland to regulate the body's energy and metabolism. Levothyroxine is given when the thyroid does not produce enough of this hormone on its own.
Levothyroxine treats hypothyroidism (low thyroid hormone). Levothyroxine is also used to treat or prevent goiter (enlarged thyroid gland), which can be caused by hormone imbalances, radiation treatment, surgery, or cancer.
Take Synthroid as a single dose, preferably on an empty stomach, one-half to one hour before breakfast. The drug is absorbed better on an empty stomach. If an infant or child cannot swallow whole tablets, you may crush a Synthroid tablet and mix it into 1 or 2 teaspoonfuls of water.
Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Call your doctor at once if you have a serious side effect such as:
- sleep problems (insomnia);
- feeling nervous or irritable;
- fever, hot flashes, sweating;
- pounding heartbeats or fluttering in your chest;
- changes in your menstrual periods; or
- appetite changes, weight changes.
Less serious side effects may include mild hair loss. This is not a complete list of side effects and others may occur.
Levothyroxine has a narrow therapeutic index. Regardless of the indication for use, careful dosage titration is necessary to avoid the consequences of over-or under-treatment. These consequences include, among others, effects on growth and development, cardiovascular function, bone metabolism, reproductive function, cognitive function, emotional state, gastrointestinal function, and on glucose and lipid metabolism. Many drugs interact with levothyroxine sodium, necessitating adjustments in dosing to maintain therapeutic response
Certain medicines can make levothyroxine less effective if taken at the same time. If you use any of the following drugs, avoid taking them within 4 hours before or 4 hours after you take levothyroxine:
- calcium carbonate (Caltrate, Citracal, Oystercal, and others);
- ferrous sulfate iron supplement;
- sucralfate (Carafate);
- sodium polystyrene sulfonate (Kayexalate, Kionex, and others);
- antacids that contain aluminum or magnesium (such as Acid Gone, Aldroxicon, Alternagel, Di-Gel, Gaviscon, Gelusil, Genaton, Maalox, Maldroxal, Milk of Magnesia, Mintox, Mylagen, Mylanta, Pepcid Complete, Rolaids, Rulox); or
- cholesterol-lowering drugs cholestyramine (Questran) and colestipol (Colestid).
If you miss a dose, take as soon as remembered; do not take if it is almost time for the next dose, instead, skip the missed dose and resume your usual dosing schedule. Do not "double-up" the dose to catch up. If you miss 2 or more doses in a row, consult your doctor.
Store at room temperature between 59 and 86 degrees F (between 15 and 30 degrees C) away from moisture and sunlight. Do not store in the bathroom. Keep away from children and pets.