Most people know that the thyroid gland is very important. It helps regulate activity of almost every body system, so it is very important to make sure this hormone is well regulated in the body. Too little thyroid hormone can cause weight gain, memory problems, fatigue, lethargy, constipation, and dry skin. Too much thyroid hormone can cause anxiety, irritability, hyperactivity, hair thinning, tremor or shaking, weight loss, and excessive sweating. The Thyroid gland is in lower part of the neck at the top edge of the breastbone. It is usually very small and can be hard to feel on exam. The thyroid gland uses Iodine to produce thyroid hormone. This is called Thyroxine, or T4 for short. Triiodothyronine, or T3 for short, is also produced in the thyroid gland to a lesser extent, converted in other tissues from T4. This T3 form of the hormone is more active than the T4 form. T4 can also be converted to “Reverse T3” instead of T3 under times of stress or with certain vitamin deficiencies. The Reverse T3 form has the opposite effect of the other thyroid hormones and can slow metabolism. If possible, I would make sure any thyroid evaluation labs include a Thyroid Stimulating Hormone (TSH), Free T4, and Free T3 along with Reverse T3 if they feel it is appropriate.