Creatine is a natural compound your body makes (in the liver, kidneys and pancreas) and also gets from meat and fish. About 95% is stored in muscle as phosphocreatine, a rapid backup that regenerates ATP — the cell's energy currency — during short, intense effort.
As a supplement, creatine monohydrate is the best-studied form. It supports gains in strength and lean muscle when paired with resistance training, and is increasingly of interest to women in midlife for muscle and bone. It is not a steroid, stimulant or fat burner. See what creatine is and creatine for women.