Teens reported use of synthetic human growth hormone without a prescription — generally with the intent of mimicking the effects of steroids — has more than doubled over the last two years, rising from 5 percent of high school students in 2012 to 11 percent in 2013, according to a new study from the Partnership for Drug-Free Kids. The partnership says that the results represent teens increasing interest in performance-enhancing substances like steroids, which synthetic human growth hormone (HGH) is often used as a substitute for. HGH naturally occurs in the body, but a synthetic version of it is available as a prescription for treating diseases, deficiencies, and issues with short stature. Because the study relies on self-reported data, its unlikely that teens are all actually using prescription HGH — instead, many may well be using supplements that are marketed as containing HGH or promoting HGH production in the body.