Roger Clemens's Congressional testimony has put pro athletes' steroid use on center stage. On Please Explain, find out what exactly steroids and human growth hormones are, how they affect the body, and why they can be so dangerous.

Leonard speaks with Dr. Timothy Hewett of The Sports Medicine Biodynamics Center at the Cincinnati Children's Hospital Medical Center; and Dr. Donald Catlin, President of the non-profit Anti Doping Research Institute.