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Hypothyroidism: woman clutching her throat. Hypothyroidism: woman clutching her throat.

Underactive thyroid

With an underactive thyroid, the thyroid gland does not produce enough hormones. This slows down the metabolism. People affected often feel lethargic, have a low heart rate and constipation.

A doctor performs an ultrasound scan of the thyroid gland. A doctor performs an ultrasound scan of the thyroid gland.

Overactive thyroid

The thyroid gland is classed as overactive when it produces more hormones than usual. This speeds up the metabolism and results in symptoms such as weight loss, perspiration or heart palpitations.