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Thyroid hormones help regulate the way the body uses energy. You need thyroid hormone replacement when you do not have enough thyroid hormones in your blood (hypothyroidism). Depending on the cause of your hypothyroidism, you may need to take thyroid hormones for the rest of your life.

Thyroid hormones are usually taken by mouth. How much you need depends on your age, your body weight, and whether you are pregnant.

Thyroid hormone replacement is the only way to treat hypothyroidism. For most people, taking a thyroid hormone medicine:

• Reduces or stops the symptoms of hypothyroidism.
• Allows them to live normal lives.
• Reduces the risk of complications from having too little thyroid hormone in the blood, including a high level of fats and cholesterol in the blood.

People who take thyroid hormones need to have their blood checked regularly to make sure that they are taking the correct dose of replacement hormone. Children, pregnant women, and older adults may need to have their blood levels checked more often than other people.

For more information about thyroid hormone replacement and hypothyroidism, see the topic Hypothyroidism.