Creatine has scientific evidence that shows it improves anaerobic performance and increases in lean body mass for some people, others may not respond to it at all. I'm a vegetarian and started taking creatine recently when I found out that not eating meat can result in lower muscle creatine stores compared to those who do eat animal flesh. I've noticed a very rapid improvement in strength and an increase in muscle size without any change in my diet or exercise routine. In regards to muscle size, much of this is a result of increased fluid retention within the muscles themselves while taking creatine. However, the potential negative of this is that fluid retention can result in increased blood pressure. There are other health concerns while taking creatine but these were from dosages that were extremely high.