 STUDY DESIGN Many patients undergo thyroidectomy for nodular thyroid disease. They have normal thyroid function prior to surgery and are immediately placed on standard thyroid hormone replacement therapy levothyroxine, LT4 after surgery. The levothyroxine dose is titrated every 6-8 weeks to normalize the thyroid stimulating hormone TSH level. The investigators aim to study this population before surgery when the patients still have endogenous thyroid function and after surgery once their TSH has been normalized to pre-surgery levels. Using a weight based dosing strategy 1.6mcgkg, most patients will remain euthyroid throughout this process. This experimental design eliminates many of the confounding variables that have plagued previous thyroid replacement trials. One of the most difficult aspects of conducting these types of studies is testing a uniform patient population. The most common cause of hypothyroidism is autoimmune thyroiditis Hashimotos thyroiditis and previous studies have largely focused on these patients. The difficulty in testing patients with autoimmune thyroid failure is that even though they have a common illness, the disease course is extremely variable. Each patient may have different degrees of thyroid failure and may still be making different amounts of endogenous thyroid hormone. The presence of thyroid autoantibodies has also been reported to have systemic effects, and may influence perception of overall health and sense of well-being. This study will focus on a more homogenous population without the potential cofounders inherent to patients with autoimmune thyroid disease. Each patient will serve as their own control and also avoid any cognitive or somatic effects that temporary hypothyroidism may induce. 