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T4 Supplement Side Effects

T4, also known as thyroxine, is a hormone produced by the thyroid glad. It contains iodine and its primary function is to increase the rate of chemical reactions in cells. T4 also helps control growth and development. Furthermore, T4 supplements are used to treat a variety of thyroid disorders. Besides thyroxine, T4 is also referred to as levothyroxine, thyroxin, L-3, L-5, and L-5'- tetraiodothyronine.

  1. The Facts

    • Thyroxine is created by the body when tyrosine (an amino acid) and iodine are combined. It enters the blood attached to plasma globulin (another protein). T4, like other thyroid hormones, are prescribed when the person's thyroid gland does not secrete enough natural thyroid hormone. These supplements cause an increase in the rate of carbohydrate metabolism as well as an increase in the rate of protein breakdown and synthesis.

    Function

    • T4 supplements excite the nervous system by acting on its endocrine system. Once administered, they remain in the body for more than a month. T4 activity is controlled by thyrotropin (a substance released by the pituitary glrand) and vice versa. Therefore, high levels of T4 depress the rate of thyrotropin secretion.

    Side Effects

    • Thyroxine is typically well tolerated; however, some side effects still exist. Most side effects originate from therapeutic overdose and include increased appetite, weight loss, insomnia, anxiety, diarrhea, heat intolerence, heart palpitations, increase in bowel movements, angina, hypertension, tachycardia and irregular periods.

    Features

    • T4 supplementation may also result in side effects on the central nervous system that include headaches, hyperactivity, nervousness, anxiety and irritability. Musculoskeletal side effects may include muscle weakness and tremors, and respiratory side effects may include dyspnea (rapid breathing). Endocrine side effects include decreased bone mineral density, reproductive side effects include impaired fertility, and dermatological side effects include flushing of the face and hair loss.

    Considerations

    • Cardiovascular side effects of thyroxine supplementation include tachycardia, arrhythmias, increased blood pressure, increased pulse rate, heart failure, cardiac arrest and myocardial infraction. Gastrointestinal side effects include vomiting, elevation in liver function and diarrhea. Other general side effects include fatigue and excessive sweating.

      Children undergoing excessive thyroid replacement therapy may experience pseudotumor cerebri (a reversible process that affects the brain) and slipped capital femoral epiphysis (separation of the ball and hip joint from the thigh bone at the upper growing end of the bone). Furthermore, infants who are overtreated with T4 supplements may experience craniosynostosis (congenital defect that causes sutures on the baby's head to close earlier than normal). They may also experience premature closure of the epiphyses (rounded end of a long bone) that results in adult height shortness.

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