What Is L-Thyroxine?

Kristeen Moore

L-thyroxine is the generic name of levothyroxine, a type of hormone that the thyroid gland produces. This gland is located at the base of the front of the neck. Thyroid hormones are responsible for helping the body to achieve a normal metabolic rate, and can even affect the heart rate, weight maintenance, and mood. When there is not enough l-thyroxine in the body, a doctor might recommend a prescription hormone replacement to equalize thyroid levels.

Hopothyroidism, or an under-active thyroid, often results from an absence of L-thyroxine.
Hopothyroidism, or an under-active thyroid, often results from an absence of L-thyroxine.

Thyroxine, also known as T4, is the medial term for levothyroxine. Triiodothyronine (T3) is the other type of hormone produced by the thyroid gland. The thyroid produces a greater amount of T4 hormones than T3 hormones. For this reason, medications that contain l-thyroxine are the most common type of drugs prescribed for patients with thyroid hormonal imbalances.

The pituitary gland produces thyroid stimulating hormones (TSH). The gland produces increased amounts of TSH when a lack of thyroid hormones is detected within the body. For this reason, a doctor might reveal that TSH levels are high in a patient that has low thyroxine levels. TSH, T4, and T3 levels are all checked through a blood test.

The most common effect of the absence of T4 is hypothyroidism, also known as under-active thyroid. This condition is marked by symptoms such as rapid weight gain and excessive fatigue, as well as cold intolerance and depression. A blood test can determine how much T4 is missing from the body. Then an endocrinologist, a type of doctor who specializes in thyroid diseases, can determine how much l-thyroxine to prescribe.

Levothyroxine dosages might be changed over the course of several months. At the same time, blood work will regularly be performed to see if the body is getting the correct amount of l-thyroxine. Once TSH and T4 levels are normal, a patient might be given the same dosage for several months or even a year at a time before another blood test is ordered again.

L-thyroxine is also used to treat a goiter in some patients. A goiter, or enlarged thyroid gland, can be caused by hypothyroidism, benign cysts on the gland, or cancer. Small dosages of levothyroxine are usually recommended to keep swelling of the gland down. This can also help prevent the occurrence of hypothyroidism in patients who do not have the condition as of yet.

Any hypothyroid symptoms will likely improve once a patient starts taking l-thyroxine. Weight gain is perhaps the most difficult thing to overcome in hypothyroidism. Levothyroxine is not a weight loss medication, and should not be used as such. The hormones that the medication produces will aid in weight loss efforts, but the drug does not directly cause weight loss.

There are certain side effects associated with l-thyroxine. In some cases, too much thyroxine can cause an overactive thyroid gland, or hyperthyroidism. Symptoms might include increased appetite, sudden weight loss, anxiety, and insomnia.

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