Treatment of the adult growth hormone deficiency syndrome with growth hormone: What are the implications for other hormone replacement therapies for hypopituitarism?

When initiating growth hormone replacement therapy, it is important to consider a patient's other pituitary hormone replacement medications, as adjustments are often necessary. Growth hormone therapy can increase the metabolism of hydrocortisone or endogenous cortisol, unmasking borderline ACTH deficiency and leading to the development of adrenal insufficiency and adrenal crisis. In addition, growth hormone can enhance the metabolism of thyroxine to triiodothyronine, uncovering borderline TSH deficiency. In many patients, thyroid hormone replacement therapy must be started, or the dose of levothyroxine must be increased. Oral estrogen replacement therapy leads to a state of relative growth hormone resistance, and the dose of GH may need to be increased substantially. Physicians have long been cognizant of the fact that adding a new prescription medication may lead to important drug-drug interactions. Starting growth hormone therapy may lead to hormone-hormone interactions that can pose serious complications for the hypopituitary patient unless the interaction of growth hormone on other pituitary hormone systems is understood.