People grow due to a hormone called the Human Growth Hormone (HGH), which stimulates the liver to produce a protein that helps the growth plate, or cartilage on the ends of bones grow, making the bone longer. The growth plate will close at the end of puberty, this happens when the cartilage is converted to bone.
Growth hormones can be administered by a pediatric endocrinologist to stimulate growth, although if the growth plates are closed then the hormone will not be effective. There is a procedure called Distraction osteogenesis in which the long bones in the body are cut and screws are placed between the bones. At intervals depending on your body type the screws are turned and the bone is separated, allowing for more bone to grow in between the two segments. This is a long and painful process but can be extremely successful; it is also the only way to grow after puberty.
