The thyroid gland is a bi-lobed gland that is found on both sides of the trachea (windpipe). It is responsible for producing the hormones thyroxine (T4) and triiodothyronine (T3). These thyroid hormones control metabolism. They also regulate body temperature and energy levels. Women are more likely than men to develop a thyroid disorder. A deficiency in thyroid hormones is termed hypothyroidism. The most common cause of hypothyroidism is Hashimoto's disease, which is an autoimmune disease where antibodies destroy the thyroid gland. The most common symptoms of hypothyroidism are weight gain, fatigue, constipation, hair thinning, and intolerance to cold.

Many other conditions can cause these same symptoms, so laboratory analysis of thyroid hormones is also appropriate in the diagnosis. The most common test is to measure thyroid stimulating hormone (TSH), but there are often inaccuracies with this test alone. Many women who have hypothyroidism have normal TSH levels. Measuring T4, T3, and TSH, as well as a good clinical history will more accurately diagnose thyroid disorders.

Hyperthyroidism is when the thyroid is over producing thyroid hormones and typically has the opposite symptoms as hypothyroidism. The most common symptoms of hyperthyroidism are weight loss, diarrhea, heart palpitations, intolerance to heat, poor memory, and muscle weakness. The most common cause of hyperthyroidism is Grave's disease, which is a condition where antibodies stimulate the thyroid gland to produce more thyroid hormones. Women are nine times more likely to develop hypothyroidism than hyperthyroidism. Approximately 10% of women have an undiagnosed thyroid condition. The basal metabolic rate drops 5% every decade of life, which is why hypothyroidism is very common in women over the age of sixty.

The endocrine hormones respond to each other and abnormal levels of hormones affect other hormones. Too much or too little thyroid hormone affects the menstrual cycle, which can result in ovulatory problems, causing infertility. Ovulatory problems also change bleeding patterns, resulting in irregular bleeding or amenorrhea. Thyroid disease can also be responsible for miscarriages. Estrogen dominance can also cause hypothyroidism, by inhibiting the uptake of thyroid hormones. Estrogen dominance is common in anovulatory states such as perimenopause. Estrogen dominance can be treated with natural progesterone. There is good evidence that hypothyroidism is responsible for causing artherosclerosis, leading to heart disease.

The thyroid gland can become enlarged, forming a goiter. Most thyroid goiters do not affect the amount of thyroid hormone released from the thyroid. All thyroid goiters need to be evaluated by a physician because a significant percentage of them are cancerous.

The underlying disorder of hypothyroidism is usually not curable. In order to treat hypothyroidism, thyroid hormone must be replaced. The most common treatment is with levothyroxine (Synthroid). Synthroid is synthetic thyroxine (T4). The problem with synthroid alone is that some people are not able to convert T4 to T3; T3 is the most active thyroid hormone. Another problem is that some people only convert T4 to reverse T4. Because of this it is also important to treat women with T3. Cytomel is a prescription form of T3. Some practitioners prefer Armour thyroid. Armour thyroid is derived from pig thyroid and contains T3 as well as T4. 

Taking too much thyroid hormone is dangerous because it can cause heart problems and osteoporosis. Hyperthyroidism is usually treated with radioactive iodine, which destroys the thyroid gland. After treatment, most of these women are now hypothyroid and need thyroid supplementation for the rest of their lives.