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What is Thyroxine?

By HERWriter
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Thyroid Conditions related image Photo: Getty Images

Your thyroid gland, which is located under the Adam’s apple area of your neck, produces two hormones. One of those hormones is called thyroxine (T4). Thyroxine is an iodine secreting hormone which regulates your metabolism.

According to the University of Maryland Medical Center, ʺT4 and T3 (triiodothyronine) hormones stimulate every tissue in the body to produce proteins and increase the amount of oxygen used by cells.ʺ

In some individuals, an increase or shortage of the hormone thyroxine may exist. Those with a shortage of the hormone thyroxine have hypothyroidism. Those with an excess amount of thyroxine have hyperthyroidism. These drugs will manage your hypothyroidism.

According to the American Thyroid Association and U.S. National Library of Medicine (NLM), symptoms of hypothyroidism may include:

• Feel cold
• Weight gain
• Dry skin
• Forgetfulness
• Hair loss
• Depression
• Fatigue
• Constipation
• Poor growth

Your doctor may order a T4 blood test to see if your thyroid is producing enough thyroxine. According to the National Institutes of Health (NIH), ʺA typical normal range is 4.5 to 11.2 micrograms per deciliter (mcg/dL).ʺ Review the results of your blood test with your doctor.

Prior to the blood test, inform your health care professional if you are taking any other medications. Some medications can interfere with a proper reading of your T4 test.

For example, the NIH states the following drugs may increase T4 measurements:

• Methadone
• Clofibrate
• Birth control pills
• Estrogens

Also, the NIH states the following drugs may decrease T4 measurements:

• Interferon alpha
• Propranolol
• Anabolic steroids
• Phenytoin
• Androgens
• Lithium
• Antithyroid drugs (for example, propylthiouracil and methimazole)
• Interleukin-2

If you have a shortage of the thyroxine hormone, your doctor may prescribe thyroxine or L-thyroxine (Levothyroxine) medication which comes in the form of a tablet. When you open your prescription bottle, you will notice the medications have a strong smell, which is typical.

The medication L-thyroxine is generally taken in the morning and only once per day. It is recommended that the medication be taken 30 minutes before your first meal.

Also, your doctor may order a follow-up blood test to see if you are responding to the hormone replacement treatment.

Side effects of thyroxine and l-thyroxine may include:

• diarrhea
• sweating
• insomnia
• palpitations
• headaches
• chest pain
• restlessness
• muscle cramps
• tremors

Contact your doctor and call 911 immediately if you feel extreme chest pains.


Thyroid Gland. University of Maryland Medical Center | Home. Retrieved September 28, 2011, from

T4 test: MedlinePlus Medical Encyclopedia. National Library of Medicine - National Institutes of Health. Retrieved September 28, 2011, from http://www.nlm.nih.gov/medlineplus/ency/article/003517.htm

thyroxine (hormone) -- Britannica Online Encyclopedia. Encyclopedia - Britannica Online Encyclopedia. Retrieved September 28, 2011, from http://www.britannica.com/EBchecked/topic/594710/thyroxine

Thyroid.org: Hypothyroidism Brochure. American Thyroid Association: Thyroid Cancer, Hyperthyroid, Hypothyroid, Thyroiditis, Thyroid Clinical Trials, Thyroid Patient Health Information. Retrieved September 28, 2011, from http://www.thyroid.org/patients/patient_brochures/hypothyroidism.html.

Blood Test: T4 (Thyroxine) . KidsHealth - the Web's most visited site about children's health. Retrieved September 28, 2011, from http://kidshealth.org/parent/system/medical/test_t4.html

Thyroxine. University of Dundee. Retrieved September 28, 2011, from http://www.dundee.ac.uk/medther/tayendoweb/thyroxine.htm

Thyroid Diseases. Lab Tests Online: Welcome!. Retrieved September 28, 2011, from

Levothyroxine - PubMed Health. National Center for Biotechnology Information. Retrieved September 28, 2011, from http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0000684

Reviewed September 28, 2011
by Michele Blacksberg RN
Edited by Malu Banuelos

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We value and respect our HERWriters' experiences, but everyone is different. Many of our writers are speaking from personal experience, and what's worked for them may not work for you. Their articles are not a substitute for medical advice, although we hope you can gain knowledge from their insight.

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