The most common thyroid problems include hypothyroidism and hyperthyroidism. Hyperthyroidism is caused by an overproduction of thyroid hormones T-3 and T-4. When these hormones are overproduced, it can lead to an increase in your body's metabolism, which can cause accelerated weight loss and heart rate irregularities. Hypothyroidism is due to an underproduction of thyroid hormones. When T3 and T4 hormones are underproduced, it can lead to a decrease in your body's metabolism, leading to weight gain and slowed heart rate. Both conditions can lead to serious health problems if not addressed. Common causes of thyroid problems include Hashimoto's thyroiditis and Graves' disease. Hashimoto's thyroiditis is an autoimmune disorder that leads to chronic inflammation in the thyroid, causing hypothyroidism. It is often a condition that runs in families. Typically, there is no cure, but when Hashimoto's thyroiditis leads to hypothyroidism, it can be treated with medication (Hashimoto's thyroiditis does not have symptoms by itself). Graves' disease is an autoimmune disease that leads to overactivity in the thyroid, causing hyperthyroidism. However, treatment of this disease with medication can lead to remission in 30%-50% of patients. Rarely, people develop thyroid cancer, which affects around 35,000 women a year. People can also develop thyroid nodules, which are small growths on the thyroid gland. These are typically harmless but should be monitored by your healthcare provider for signs that they are cancerous.