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Medical Author:

Robert Ferry Jr., MD

Robert Ferry Jr., MD

Robert Ferry Jr., MD, is a U.S. board-certified Pediatric Endocrinologist. After taking his baccalaureate degree from Yale College, receiving his doctoral degree and residency training in pediatrics at University of Texas Health Science Center at San Antonio (UTHSCSA), he completed fellowship training in pediatric endocrinology at The Children's Hospital of Philadelphia.

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Medical Editor:

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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There are two main purposes for taking thyroid hormone:

1. to replace the thyroid hormone levels when your thyroid is underactive (hypothyroidism), and
2. to suppress further growth of thyroid tissue, in the treatment of thyroid cancer or benign nodular thyroid disease.

L-thyroxine (also called LT4 or levothyroxine)

L-thyroxine is the most commonly used form of thyroid hormone.

• This medicine contains the synthetic form of a thyroid hormone
• L-thyroxine as medication is identical to the L-thyroxine which is the major hormone made by the thyroid gland
• L-thyroxine is the most commonly prescribed form of thyroid hormone replacement

Initial L-thyroxine dose

• The initial dose of LT4 is based on age, weight, and medical history.
• Current brands include:
  • levothyroxine (Levoxyl, Synthroid, Levoxyl, Unithroid)
  • Multiple generic forms of L-thyroxine including but not limited to Levothroid

Physicians should be aware of the following conditions that their patients may also have when prescribing L-thyroxine:

• Heart disease
• High blood pressure
• High cholesterol or atherosclerosis (hardening of the arteries)
• Diabetes
• History of overactive thyroid
• Underactive adrenal gland
• Underactive pituitary gland.

L-thyroxine is taken once each day by mouth

• Stable blood levels of thyroid hormone are achieved when L-thyroxine is taken at approximately the same time each day, ideally the first thing in the morning on an empty stomach.
• Avoid taking food within 1 hour and avoid calcium, iron sucralfate, aluminum-containing antacid, and multivitamins within 2 hours before or after the dose.
• If a dose is skipped, two doses may be taken the following day.

Blood levels of thyroid stimulating hormone (TSH) should be checked approximately 4-6 weeks following each adjustment of LT4 dose.

• L-thyroxine comes in oral forms, for patients to use at home, and intravenous forms used in a hospital-setting.

• L-thyroxine during pregnancy and breastfeeding:

  • It is safe to take L-thyroxine during pregnancy.
  • The dose of L-thyroxine often must be increased during the first 20 weeks of pregnancy. TSH testing is recommended immediately after pregnancy is confirmed.

Side effects that your physician should be aware of include:

• chest pain, shortness of breath or palpitations,
• anxiety,
• flushing and sweating,
• severe headaches,
• vomiting,
• diarrhea,
• weight loss,
• abnormal menses, and
• Sleeping disturbances

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