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What is Thyroxine?

Tricia Christensen
Updated May 17, 2024
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Thyroxine (T4) is one of the hormones produced by the thyroid gland that helps regulate the adrenal system, and plays a role in energy, normal growth and development, ability to maintain a healthy weight, and in mood stability. The other hormone produced by the thyroid gland is T3 or triiodothyronine. Both of these hormones get produced when the pituitary gland creates thyroid-stimulating hormone (TSH). Either of these hormones may be excessive (hyperthyroidism) or below normal levels (hypothyroidism) and this can have serious effects on the body.

Thyroid hormones are essential. An inadequate supply in infants and children, for instance, can retard growth and cause mental retardation. In many countries, thyroid levels are checked on infants to make certain they have a functioning thyroid gland. In adults with low amounts, a number of the body’s systems may not work as well as they should. The body’s metabolism may be depressed, leading to easy weight gain, and even things like poor respiration and cardiac output.

Thyroxine’s effect on mood and mental illness is beginning to be studied extensively. There is increasing evidence that people with conditions like major depression and bipolar disorder may have low levels of thyroid function. There is also some evidence that current laboratory levels suggesting normal range may not be accurate when it comes to treating low levels of thyroid hormones, and the scale of what is considered normal has been adjusted several times. Doctors are urged not to overlook low normal readings anymore, as these may be medically significantly.

When the body fails to produce adequate T4, this can be discovered via blood sampling, as stated. Initial tests may be called TSH tests and only evaluate the level of thyroid stimulating hormone. If TSH is not correct, doctors might then order T4 and T3 tests to look at the specific levels of each hormone. Should thyroxine be low, doctors may suggest supplementation with medications called levothyroxine. This is the chemical version of T4, which is also known by the brand name Synthroid®.

There is a body of evidence suggesting supplementation with levothyroxine may not be as helpful as supplementation with the brand-name drug. Part of this may relate to the instability of drug versions of T4. Different formulations, may actually work differently and a high number of people report problems with generic types, especially when switching from one generic manufacturer to another. There are still many in the medical field who argue that generic thyroxine is just as good as Synthroid®, but a number of doctors now appear to agree with patients who use thyroid supplementation that there is an appreciable difference.

As important as having adequate thyroxine is, it’s also important not to have too much. High levels may lead to weight loss, sweating, tremor, and enlargement at the neck where the thyroid gland is located. Prolonged hyperthyroidism may cause significant hair loss, heart problems, and development of osteoporosis. When these symptoms are present, the goal is to reduce amount of T4 and T3. This might be accomplished by removing the thyroid gland and supplementing with levothyroxine or by giving medications that may suppress thyroid gland function.

WiseGeek is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Tricia Christensen
By Tricia Christensen
With a Literature degree from Sonoma State University and years of experience as a WiseGeek contributor, Tricia Christensen is based in Northern California and brings a wealth of knowledge and passion to her writing. Her wide-ranging interests include reading, writing, medicine, art, film, history, politics, ethics, and religion, all of which she incorporates into her informative articles. Tricia is currently working on her first novel.
Discussion Comments
By andee — On May 23, 2011

I also have a good success story from using Thyroxine to help control my thyroid gland. I felt tired all the time and had put on an extra 20 pounds. For a long time I just figured it was from getting older and not being as active.

I had tests done to check my thyroid and began using Thyroxine on a daily basis. I have not had any negative thyroxine side effects, but have been able to lose 15 pounds. I also have much more energy and do not get so tired as the day wears on. I know it is important to keep a close watch on your levels, so you can keep your body in balance. Why are we always so amazed that we feel better when things are balanced?

By myharley — On May 20, 2011

Regulating thyroid levels is also important in your pets. I had a golden retriever who was losing most of her hair, had put on a lot of weight and did not have much energy. When I took her to the vet he discovered that she had low thyroid readings. I began giving her one Thyroxine a day.

It was amazing to see the difference. Her coat grew back beautifully, over time she lost 30 pounds and had the energy of a puppy. She was on a low thyroxine dosage of one pill a day, but remained on it for the rest of her life. I am thankful that I had her checked out when I did so she could get the proper treatment and feel better.

By LisaLou — On May 19, 2011

The thyroid gland and adrenal glands are more important to our bodies staying balanced than I think many people realize. When I went to my doctor complaining about fatigue one of the first things he did was check my thyroid levels. They were low, so I began taking thyroxine and have noticed an improvement.

Because it is important to have a good balance and not have too much or too little, I regularly have my thyroxine levels checked. I am not sure what causes someone to have low thyroid levels, but the difference in energy levels is significant.

Tricia Christensen
Tricia Christensen
With a Literature degree from Sonoma State University and years of experience as a WiseGeek contributor, Tricia...
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