When you use a drug such as heroin or speed on a regular basis your whole life seems to revolve around it. You push away your loved ones. You lose ambition and even the will to get up in the morning. You become isolated in your own world which is a sure way of driving you insane. The deeper you get, the more dangerous it becomes.
Excessive use makes the amount increase as the buzz becomes harder and harder to obtain.
Taking any sort of drug is a risk, but the one thing that is certain is that it becomes boring after a while. So you start to mix, which is not only a dangerous cocktail but also another step to not being able to get a buzz on lighter drugs. Violence follows, violence towards the people you love, people you should never hurt and yet you have. Then you come down, and the realisation of what you have done gives you incredible guilt, guilt you cannot deal with. The feelings that go on in your head become so bad you take more and more to obliviate them, until one day you really don't care anymore.