A.  Thyroid stimulating hormone (TSH) is a hormone, which is released from the pituitary gland and it regulates the production of thyroid hormones T3 and T4) from the thyroid gland. Its level is regulated by a negative feedback mechanism from T3 and T4, which means that if T3 and T4 are low, the TSH level goes up and when T3 and T4 are high, the TSH levels go down. While treating thyroid hormone deficiency, as thyroid hormone pill is given the TSH levels become normal once the dose is appropriate. Thyroid hormone dose fluctuation can be related to variable compliance with medications, or any factors that affect its absorption from the gut, like taking it along with food, vitamins, calcium, etc.