Synthetic thyroid hormones used to treat underactivity of the thyroid gland
In hypothyroidism, the thyroid gland produces insufficient amounts of thyroid hormones, particularly thyroxine, causing symptoms such as tiredness and weight gain. This disorder can be caused by inflammation of the thyroid gland, known as thyroiditis, which may be either a short-term or long-term condition. Hypothyroidism may also be the result of previous radioiodine treatment for over-activity of the thyroid gland (see Drugs for hyperthyroidism), or it may be present from birth (see Inborn errors of metabolism). Hypothyroidism usually needs lifelong treatment with synthetic thyroid hormones.
How are they used?
Newborn babies who have hypothyroidism may initially need injections of the hormones. In adults, synthetic thyroid hormones are taken orally every day. Drugs are started at a low dose and the dose is increased gradually until an effective level is reached without causing side effects. The drugs take a few weeks to become effective, and it may take up to 6 months for symptoms to disappear completely.
What are the side effects?
Given at the correct dose, synthetic thyroid hormones cause no side effects. To ensure that the correct dose is maintained, you will have regular blood tests. If the dose that you are given initially is too high, you may develop symptoms of hyperthyroidism, which may include tremor, weight loss, and rapid, sometimes irregular heartbeat. These symptoms will disappear once the correct dose for you has been established.
From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.
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