Some people turn to a substance called human growth hormone (HGH) in hopes that it will keep them feeling and looking youthful. But experts say that hope is unfounded. And worse, these products can be harmful.

HGH, produced by the pituitary gland, spurs growth in children and adolescents. It also helps to regulate body composition, body fluids, muscle and bone growth, sugar and fat metabolism, and possibly heart function. Produced synthetically, HGH is the active ingredient in a number of prescription drugs and in other products available widely over the Internet.