http://au.news.yahoo.com/thewest/a/-/br ... gs-charge/One book I read about Heroin addiction written by a medical addiction specialist was called something like, "It's so good, don't even try it once!".
In medical practice I've found two groups who are prone to turning to drug use:
1. Those who had traumatic upbringings.
2. Those who, when you look back, were developing illnesses like Bipolar Disorder or Schizophrenia and had not gone for medical help first.
There is also evidence that some people are genetically more prone to become addicted to alcohol and drugs than others.
These may be the ones who get hooked when trying these things out as party drugs, then rationalise their addiction to themselves.