A hormone is a chemical made by specialized cells, usually in an endocrine gland, and it is released into the bloodstream to send a message to another part of the body. Since hormones are released into the bloodstream and can therefore be transported throughout the body, they can perform these two actions on many different targets. The complex interaction between the glands, hormones and other target organs is called the endocrine system. Hormones affect many physiological activities, including growth, metabolism, appetite, puberty and fertility. The best and most popular hormones on the market in 2020 are found on this page.