According to Dr. Bernard Robaire, a professor in obstetrics and gynecology at McGill University, men produce about 100 million sperm per day - about 1,000 sperm for every heartbeat. So in the vast majority of cases, improving sperm count and quality is all about providing healthy nutrients to make sperm, and making sure that one's lifestyle choices aren't damaging one's sperm. Put another way, men don't have to do much to increase overall sperm production; the focus should be on providing the right materials to produce healthy sperm, and then keeping those sperm healthy.
One study appeared to show that gw 50156 side effects included the growth of cancer cells but on further inspection, the results could be considered misleading. The study of gw1516 which was carried out on mice included 1000 times the recommended dose, taken over a prolonged period of time. As no individual would be taking such an inflated level of gw501516, there is debatable value attached to this particular study. Nevertheless, despite the criticism of this study, it was sufficient for GSK to drop the project so shouldn’t be dismissed completely.