What are the effects of cannibalism ?

Today my friend and i were talking about vampires/cannibals/etc. and he told me that drinking human blood can deteriorate your body or something. He'd seen a doentary about a guy who had been a cannibal and he had a whole lot of problems with his organs and stuff. So when i got home i looked up if human blood was harmful to the body and i couldn't find anything. Can anyone tell me what the side effects of cannibalism are?