• headache;

• sleep problems (insomnia);

• nervous or irritable feeling;

• fever, hot flashes, sweating;

• changes in your menstrual periods;

• 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. Tell your doctor about any unusual or bothersome side effect.

What other drugs will affect levothyroxine?

The following drugs may cause medical problems if you use them with levothyroxine: lithium, amiodarone, or antidepressants. Tell your doctor if you have recently received radiation therapy with iodine (such as I-131).

This list is not complete and there are many other drugs that can interact with levothyroxine. Tell your doctor about all the prescription and over-the-counter medications you use. This includes vitamins, minerals, herbal products, and drugs prescribed by other doctors. Do not start using a new medication without telling your doctor.

Certain medicines can be continued, but they may make levothyroxine less effective if taken at the same time. If you use any of the following drugs, use them at least 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 (Amphojel, Gaviscon, Maalox, Mylanta, Riopan, Rulox, Tums, and others); and

• cholesterol-lowering drugs cholestyramine (Questran) and colestipol (Colestid).