<Li> Hyperthyroidism (an example is Graves Disease) is the clinical syndrome caused by an excess of circulating free thyroxine, free triiodothyronine, or both . It is a common disorder that affects approximately 2% of women and 0.2% of men . Thyrotoxicosis is often used interchangeably with hyperthyroidism, but there are subtle differences . Although thyrotoxicosis also refers to an increase in circulating thyroid hormones, it can be caused by the intake of thyroxine tablets or by an over-active thyroid, whereas hyperthyroidism refers solely to an over-active thyroid . </Li> <Li> Hypothyroidism (an example is Hashimoto's thyroiditis) is the case where there is a deficiency of thyroxine, triiodothyronine, or both . </Li> <Li> Clinical depression can sometimes be caused by hypothyroidism . Some research has shown that T is found in the junctions of synapses, and regulates the amounts and activity of serotonin, norepinephrine, and γ - aminobutyric acid (GABA) in the brain . </Li> <Li> Hair loss can sometimes be attributed to a malfunction of T and T. Normal hair growth cycle may be affected disrupting the hair growth . </Li>

When t3 and t4 are needed iodinated thyroglobulin