Somatropin injection is used to replace growth hormone (a natural hormone produced by your body) in adults and children with growth hormone deficiency. Somatropin injection is also used to increase growth in children with certain conditions that affect normal growth and development. Somatropin injection (Serostim) is used to increase body weight and physical endurance in patients with human immunodeficiency virus (HIV) who have HIV-associated wasting syndrome. Somatropin injection (Zorbtive) is used to treat short bowel syndrome in adults who are receiving additional nutrition or fluids from intravenous (IV) therapy. Somatropin is a human growth hormone (hGH) analog. It works by replacing growth hormones that are normally produced in the body, which may result in increased growth, body weight, and improved absorption of nutrients and fluids from the intestines.