Common Uses:Off Label Uses:Side Effects:
Side effects typically occur when the Levothroid dosage is too high. Too much Levothroid causes symptoms of an overactive thyroid (known medically as hyperthyroidism). These symptoms can be dangerous, and any of these symptoms should be reported to your healthcare provider (as they may signal that your Levothroid dosage needs to be decreased). These side effects may include:

Feeling hot all the time and increased sweating
Fever
Hyperactivity, nervousness, anxiety, or irritability
High blood pressure (hypertension)
Insomnia (see Levothroid and Insomnia)
Broken bones or other signs of weakened bones
Menstrual problems or fertility problems
Shakiness (tremors) or muscle weakness
Heart palpitations
Emotional changes
Hair loss (see Levothroid and Hair Loss)
Flushing
A rapid heart rate (tachycardia)
Heart failure, chest pain, or a heart attack
Difficult or painful breathing
An increased appetite, along with weight loss
Diarrhea, vomiting, or abdominal cramps (stomach cramps)
Seizures.

As with any medication, Levothroid can also cause allergic reactions. Seek medical attention immediately if you develop signs of an allergic reaction, including:

An unexplained rash or hives
Itching
Wheezing or difficulty breathing
Unexplained swelling (especially of the lips, mouth, or throat).

Cautions / Warnings:Drug Interactions:
Levothroid or levothyroxine sodium may interact with several other medications, including numerous non-prescription products. Some of the medicines that may potentially lead to Levothroid interactions include:

Antacids or gas-relieving medications
Antidepressant medications
Calcium products, including vitamin supplements and calcium-rich foods
Certain seizure medications, such as:

Carbamazepine (Carbatrol®, Epitol®, Equetro®, Tegretol®)
Phenobarbital (Luminal®)
Phenytoin (Dilantin®, Phenytek®)

Cholestyramine (Prevalite®, Questran®, Questran® Light)
Colestipol (Colestid®)
Diabetes drugs, including insulin and oral diabetes medications
Digoxin (Digitek®, Lanoxin®)
Estrogens, such as birth control pills, patches, rings, or hormone replacement therapy (HRT)
Iron (including iron found in multivitamins)
Orlistat (Alli™, Xenical®)
Raloxifene (Evista®)
Rifampin (Rifadin®)
Sucralfate (Carafate®)
Theophylline (Uniphyl®, Theocron®, TheoCap®, Theo-24®, Elixophyllin®)
Warfarin (Coumadin®, Jantoven®).