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Synthroid

Generic Name: 

Levothyroxine sodium

Brand Names: 

Levothroid, Levoxyl, Synthroid, Unithroid

Synthroid Description: 

Synthroid is a synthetic form of the thyroid hormone thyroxine, also known as T4. Synthroid is a replacement therapy medication that is usually taken for life by people with hypothyroidism, a condition involving an inadequate production of thyroid hormone.

Synthroid Side Effects: 

Side effects of Synthroid resemble those of hyperthyroidism and include:

  • Anxiety
  • Diarrhea
  • Excessive sweating
  • Fatigue
  • Flushing
  • Headache
  • Heat intolerance
  • Increased appetite
  • Insomnia
  • Irritability
  • Menstrual irregularities
  • Tremors
  • Vomiting
  • Weight loss

 For more information, see our Synthroid side effects page.

Synthroid Uses: 

Synthroid is mainly prescribed in the treatment of hypothyroidism, a condition in which the thyroid gland does not produce enough thyroid hormone to regulate metabolic processes or allow for normal growth and development. Synthroid is effective as a supplemental or replacement therapy for people with underactive thyroid glands.

Hypothyroidism commonly affects women, especially those over 50, and if left untreated, can lead to joint pain, infertility, heart disease, and obesity. Symptoms of hypothyroidism include fatigue, increased sensitivity to cold, constipation, pale or dry skin, facial puffiness, a hoarse voice, weight gain, depression, muscle weakness, and brittle hair or fingernails.

Synthroid can also be used to decrease the size of the thyroid glands in people with goiter, a condition involving a benign enlargement of the thyroid gland. Synthroid can also treat thyroid cancer.

Synthroid Interactions: 

Do not take Synthroid within 4 hours of taking iron or calcium supplements, antacids, or orlistat, as the absorption of Synthroid can be decreased.

Synthroid has the potential to interact with many different medications, so talk with your doctor before combining any medications with your treatment. Some of the drugs that have been shown to interact with Synthroid include:

  • Anticoagulants
  • Antidepressants such as tricyclics, tetracyclics, and selective serotonin reuptake inhibitors (SSRIs)
  • Carbamazepine
  • Diazepam
  • Estrogen-containing oral contraceptives
  • Glucocorticoids
  • Heparin
  • Insulin
  • Ketamine
  • Lovastatin
  • Methadone
  • Non-steroidal anti-inflammatory drugs (NSAIDs)
  • Phenobarbital
  • Rifampin
  • Sympathomimetics
  • Tamoxifen

See your doctor or the Synthroid medication guide for a more complete listing of drug interactions.

Synthroid Dosage Information: 

Typical Dosage Recommendations

Synthroid is usually taken as a single, daily dose. Doses should be taken on an empty stomach, approximately 30 minutes to 1 hour before eating breakfast.

Dosage depends on body weight and other factors, but generally, the dosing is as follows:

  • Adults and teenagers: 1.7 microgram (mcg) per kg of body weight per day
  • Children 0 to 3 months: 10-15 mcg/kg/day
  • Children 3 to 6 months: 8-10 mcg/kg/day
  • Children 6 to 12 months: 6-8 mcg/kg/day
  • Children 1 to 5 years: 5-6 mcg/kg/day
  • Children 6 to 12 years: 4-5 mcg/kg/day
  • Children over 12 years (with growth and puberty incomplete): 2-3 mcg/kg/day
  • Children over 12 years (with growth and puberty complete): 1.7 mcg/kg/day

Elderly adults are typically prescribed smaller doses of less than 1 mcg/kg/day.

Missing a Dose of Synthroid

If a dose of Synthroid is missed, take the missed dose as soon as you remember. If it is almost time for your next scheduled dose, skip the missed dose and wait to return to your regular dosing schedule.

Synthroid Overdose

Seek emergency medical attention if you believe you have overdosed on this medication. Symptoms of overdose are similar to those of hyperthyroidism (rapid heartbeat, anxiety, fatigue, difficulty sleeping, tremor, irritability) and may additionally include confusion and disorientation.

Synthroid FDA Approval: 

July 24, 2002

Synthroid Recall/Black Box Warning Information: 

There is a Black Box warning on Synthroid and other thyroid hormone medications alerting consumers that thyroid hormones should never be used for weight loss. In patients with normal thyroid function, doses of thyroid hormones are ineffective for weight loss, and larger doses may lead to serious or potentially fatal cases of toxicity, especially if given in conjunction with sympathomimetic amine drugs that are frequently used for weight loss.

Sources: 
  1. http://www.synthroid.com/PrescribingInformation.cfm?CFID=748289&CFTOKEN=65676182
  2. http://www.mayoclinic.com/health/drug-information/DR602749
  3. http://www.accessdata.fda.gov/scripts/cder/drugsatfda/index.cfm?fuseaction=Search.Overview&DrugName=SYNTHROID
  4. http://www.mayoclinic.com/health/hyperthyroidism/DS00344/DSECTION=symptoms
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