Hypothyroidism is an underactive thyroid gland producing insufficient thyroid hormone: TSH is elevated, free T4 is low or low-normal. It slows metabolism and drives fatigue, weight gain, and cold intolerance, and is distinct from Hashimoto's thyroiditis (the autoimmune cause), though the two frequently co-occur. This page covers the three parts of working with hypothyroidism in one place: metabolic diagnostics, the correction protocol, and how the online consultation itself works.