It seems that substance-abuse is often a response to underlying, and usually undiagnosed, psychological/emotional/mental issues (depression, ADHD, FAS, etc.); hence the term 'self-medicating'. Criminal behaviour is often linked as well. Most people behind bars were probably in desperate need of mental health therapy long before their legal troubles began. Knowing this doesn't necessarily make such people any easier to deal with, though ... you do have to keep yourself healthy before you can help anyone else - and that might necessitate avoiding the people you wish you could help.