I work in a pharmacy, I see this question a lot! There are so many answers. Heart problems and neurological problems are the number two issues that you will see. It will clearly cause addiction, but that’s tied with the word “abusing”. Psychological issues will be a big follow up issue as well that a lot of people don’t take as serious. Over dosing comes almost too fast for us to list all the chain reactions. Everything gets messed up when you don’t take medicine correctly.