Hormones are typically classified into three groups, based on their chemical structure rather than their function. These three groups are steroids, amines, and peptides.

All the steroid hormones, except retinoic acid, are lipids synthesized from cholesterol through a series of biochemical reactions. 17b -Estradiol is perhaps one of the few most discussed hormones in this group, as it is the active form of estrogen responsible for the development of many female sex characteristics. Testosterone, having a structure similar to estradiol, is an androgen responsible for the development of many male characteristics. These steroids are referred to as sex hormones and are secreted by the adrenal cortex, the placenta, and mostly the gonads. Some other steroid hormones are aldosterone, corticosterone, and progesterone.

Amine hormones are (almost) all derived from the amino acid tyrosine. They are secreted by the adrenal medulla but largely by the thyroid, and are typically stored as granules in the cytoplasm until needed. Epinephrine and thyroxine are the notable ones in this group.

Most hormones are peptides, thus each having only a short chain of amino acids. They are secreted by several tissue organs including the pituitary, parathyroid, heart, stomach, liver, and kidneys. Many hypothalamic factors (e.g., gonadotropin- and growth hormone-releasing hormones) and pituitary hormones (e.g., growth hormone, thyroid-stimulating hormone) belong to this peptide group. Also included in this group are insulin and glucagons. These peptide hormones are synthesized largely as proteins on the ribosomes first, and then cleaved into the size of amino acids. Some of them also serve as neurotransmitters.