When the thyroid gland is unable to produce a satisfactory level of thyroid hormones, hypothyroidism may develop. The hormones produced by the endocrine or thyroid gland are responsible for the regulation of a person's metabolism; hence, an injury to this gland or an abnormality in its hormone production will directly affect the metabolic rate of the body. Deficient quantities of thyroid hormones can decrease the metabolic rate of a person's body.

Hypothyroidism is characterized by several signs and symptoms that may lead to serious health risks and severe complications. Due to sluggish metabolic rate, a person suffering from hypothyroidism may experience lack of vigor and drowsiness, chronic physical fatigue, difficulty in withstanding coldness, weight gain despite loss of appetite, severe constipation, and abnormal menstrual cycles in women. Other early symptoms observed in hypothyroid patients are persistent headaches, swelling of the face and muscle cramps, chest pain and difficulty in breathing, enlarged thyroid gland or goiter, dry hair and pale skin, difficulty concentrating, and decreased memory retention. These early symptoms of hypothyroidism are often misconstrued as manifestations of other health disorders such as menopause, stress, or aging.

Failure to undergo proper treatments will aggravate a hypothyroid's condition. In such case, other symptoms may occur and, over time, develop into serious or even fatal complications. The patient may suffer from memory loss, loss of hearing and eyesight, numbness, severe depression, and incurable mental impairment or dementia. Extreme cases may lead to myxedema coma, a form of hypothyroidism characterized by adverse physiological changes like enlarged tongue, bulging eyes, and swollen face, and behavioral and mental maladies such as delirium, completely suspended feeling or apathy, seizures, and, at the worst, coma.

In addition, children with congenital hypothyroidism have any or all of the following symptoms: jaundice or yellowish skin, rugged breathing, constipation, delayed teething, and loss of appetite. If they remain untreated, lumps may appear beneath their skin due to fatty build-up, making them look swollen and bulging.

The aforementioned symptoms may be observed in hypothyroid patients, regardless of age or gender. It is worth noting, however, that each hypothyroid patient differs from other patients in terms of the number of symptoms present and the severity of the experienced symptoms. Patients may complain about different natures and varied intensity of these symptoms.