Hormones are powerful, complex chemicals that are normally produced by the endocrine system (pituitary, thyroid, adrenal glands, pancreas, ovaries and testes, etc.) and transported through the bloodstream to stimulate or inhibit metabolism in target glands or organs. Some hormones like epinephrine have powerful effects throughout the body; others have their effects on a specific brain region or organ. Hormones continuously interact in a complicated feedback cycle; if this cycle is disrupted, the level of hormones may rise or drop from normal levels, causing altered metabolism.