Synthroid Medication Information

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Synthroid, also known as levothyroxine, is a medication used in the treatment of hypothyroidism (underactive thyroid). Normally produced thyroid hormone is replaced by this medication. Other thyroid disorders may also be treated by this medication, such as certain types of goiters, thyroiditis, thyroid nodules, and thyroid cancer.


This medication is typically taken once daily, 30 to 60 minutes before breakfast on an empty stomach. However, all patients should take this exactly as directed. This medication is taken orally.

Side Effects

Patients may experience headache, trembling, increased appetite, weight loss, nervousness, sweating, diarrhea, and insomnia. Though rare, during the first few months of use, patients may experience hair loss. This side effect is most often temporary and will usually stop once the body is used to this drug.

There are some serious side effects that are unlikely, but will require emergency medical attention. These may include chest pain, shortness of breath, irregular or rapid heartbeat, and seizures.

Though unlikely, an allergic reaction is possible. This is a medical emergency. Some signs include swelling (specifically affecting the tongue, throat, or face), difficulty breathing, and dizziness.


Certain medical conditions may be adversely affected by this drug or may be contraindicated with it. These include overactive thyroid conditions, adrenal gland problems, and heart attack. Other possible contraindications may include heart problems, diabetes, bone loss disease, hormone deficiencies, certain thyroid problems, female or male infertility issues, other hormone disorders, blood clotting disorders.

Drug Interactions

Before starting this medication is it important to know that certain other medications may interact. Other medications that may interact with Synthyroid include warfarin, estrogen products, amiodarone, lithium, androgens/anabolic steroids, high-dose salicylates, rifamycins, antidepressants, growth hormones, theophylline, digoxin, diabetes medications, iodide, anti-thyroid agents, glucocorticoids, phenobarbital, beta blockers, cytokines, and ketamine.

Certain medications may reduce how well this drug is absorbed into the bloodstream and, therefore, should not be taken within four hours of Synthyroid. These include calcium supplements, antacids, orlistat, colesevelam, sucralfate, iron supplements, simethicone, cholestyramine, colestipol, and sodium polystyrene sulfonate.


This medication should never be used for weight loss or to treat obesity, either with diet pills or alone. Doing so could result in serious side effects, including some that could be life-threatening. When taken in large doses, especially in combination with diet pills, toxicity symptoms may occur.

This medication has been shown to be able to be used when pregnant. However, a dose adjustment will be necessary. This drug will pass into breast milk in small amounts so before breastfeeding all patients must consult their physician.

The elderly may be more sensitive to the side effects of this drug. Children’s future height may be affected by this drug if it is overused.

Before having any dental work done or any surgical procedures, all patients must let their doctor or dentist know they are taking this drug.


RxList. (2010). Synthyroid. Retrieved on November 20, 2010 from RxList:

United States National Library of Medicine National Institutes of Health. (2008). Levothyroxine. Retrieved on November 20, 2010 from PubMed Health: