Initially, the primary method of breeding giant pandas in captivity was by artificial insemination, as they seemed to lose their interest in mating once they were captured. This led some scientists to try extreme methods, such as showing them videos of giant pandas mating and giving the males sildenafil (commonly known by name Viagra). Only recently have researchers started having success with captive breeding programs, and they have now determined giant pandas have comparable breeding to some populations of the American black bear, a thriving bear species. The normal reproductive rate is considered to be one young every two years.