One of the scariest things about the effects of human growth hormone on the brain is that it can lurk unnoticed for years. Take Bertil Fox; for most of his life, the St. Kitts-born muscle pro was a genial sort, famous for his incredible muscle density. After winning multiple titles in England and the United States, he returned to St. Kitts with his wife to start his own gym. Then one day in 1997, he walked into the dress shop that his mother-in-law owned and shot her and his wife with a pistol. He claims that it was in self-defense, but the evidence was against him and he was sent to jail for life.