WHAT IT IS: Human growth hormone, or HGH, is a protein produced by the pituitary gland.

WHAT IT DOES: It stimulates overall growth.

WHAT THE HEALTH RISKS ARE: Over-production of human growth hormone, or overuse by healthy individuals, has been linked to cardiovascular problems, diabetes, an increased risk of some cancers and enlarged limbs and features.

OVERVIEW: Until 1981, HGH deficiencies were treated with growth hormone extracted from cadavers. Pharmaceutical versions of human growth hormone that have since been developed are considered safer and just as effective. With the introduction of such products to the medical marketplace, athletes in the 1990s began using HGH to build size and strength, and anti-aging or wellness clinics began prescribing it to slow down the process of aging — though there is no substantial medical evidence to support either use.

In 2003, the Food and Drug Administration approved HGH for use in extremely short children whose stunted growth did not have a known cause, leading to increases in prescriptions of the drug. Though long banned in most pro sports, human growth hormone cannot be detected in standard urine tests. A blood test developed to detect HGH has been in use since the 2004 Summer Olympics, though the only U.S. pro sport to employ it is Major League Baseball.

— Amy Shipley