I'm well aware of off label use, and they often do find that what works for one illness works for another. But the approval is done in a controlled environment and the side effects are noted. In other words, people just aren't reading about something on the internet and deciding that they'll take it for another problem. They usually are under medical solution.
Now, I don't believe in vitamins and supplements - I personally believe they are a waste of money, and can be quite dangeroous if taken in the wrong dosage - more is not better. I believe it is better to get your vitamins and minerals from the foods we eat and if we eat a healthy diet, there is no need for additional pills. But I am not going onto various websites decrying that other people shouldn't take them. You know it is big business, because every drug store you go into has aisles full of the stuff. People believe in them. Additionally there are the "brain" supplements that claim to help your memory - I've done research and my research has found that these claims are bogus. But if you believe in it, and you think it is helping you, then so be it.