Synthroid is a brand name for the drug levothyroxine, a thyroid hormone replacement medication for people with an underactive thyroid, or hypothyroidism. Synthroid effects mimic those of naturally occurring thyroid hormones, thereby alleviating the symptoms of hypothyroidism. Excessive amounts of levothyroxine can lead to symptoms similar to hyperthyroidism, or thyroid hormone excess. The U.S. Food and Drug Administration reports that 13 million Americans take various brands of levothyroxine.
Restoration of Metabolic Rate
Thyroid hormones control the activity level of the body organs or the metabolic rate. People with hypothyroidism have an abnormally low metabolic rate, leading to decreased body temperature, cold intolerance and weight gain, notes The Merck Manual for Healthcare Professionals. Levothyroxine administration restores the metabolic rate to a normal level and halts the weight gain associated with hypothyroidism.
Improved Cognition
Hypothyroidism commonly causes slowed mental function. Patients commonly exhibit forgetfulness and difficulty learning new information, reports the American Association of Clinical Endocrinologists. Restoring the thyroid hormone level to a normal range with the administration of Synthroid leads to normalization of brain function. Patients with hypothyroidism typically experience sustained improvement in their cognitive abilities after beginning levothyroxine treatment. In a December 2009 study published in the "European Journal of Endocrinology," Dr. Caroline Kramer and colleagues report finding no difference in cognitive functioning between older adults without thyroid problems and those on long-term thyroid hormone replacement therapy.
Correction of Depression
Many patients with hypothyroidism have depression, reports the Columbia University Medical Center Department of Surgery. Treatment with Synthroid usually reverses hypothyroidism-induced depression. The effect of thyroid hormones on mood proves significant, as is evidenced by the fact that doctors sometimes prescribe low doses of thyroid hormones, such as levothyroxine, for patients with treatment-resistant depression.
Nervousness, Irritability and Insomnia
Adjusting the dose of levothyroxine to achieve a normal level of thyroid hormones in the body without overshooting the mark sometimes proves challenging. Patients receiving too much Synthroid commonly exhibit nervous system symptoms, including nervousness, irritability and insomnia, notes the National Library of Medicine encyclopedia MedlinePlus. Decreasing the dose of the medication corrects this adverse side effect of the drug.
Diarrhea and Weight Loss
An excessive amount of levothyroxine can abnormally elevate the metabolic rate, leading to unintentional weight loss, reports MayoClinic.com. Increased intestinal motility caused by the drug may lead to diarrhea, further contributing to weight loss.
Decreased Bone Density
The manufacturer's FDA-approved prescribing information for Synthroid warns that women on long-term levothyroxine therapy may experience loss of calcium and phosphorus from the bones, leading to bone fragility. This effect typically proves most profound among postmenopausal women. To reduce the risk for this side effect of Synthroid, the manufacturer recommends using the lowest dose possible to restore normal thyroid hormone levels.
References
- U.S. Food and Drug Administration: Postmarket Drug Safety Information for Patients and Providers, Levothyroxine Sodium Product Information
- The Merck Manual for Healthcare Professionals: Hypothyroidism (Myxedema)
- American Association of Clinical Endocrinologists: Hypothyroidism
- "European Journal of Endocrinology"; Treated Hypothyroidism, Cognitive Function, and Depressed Mood in Old Age: the Rancho Bernardo Study. Caroline K. Kramer, M.D., et al.; December 2009
- Columbia University Medical Center Department of Surgery: Hypothyroidism
