My sister says she has cocaine abuse. are family members more likely to get the same thing?

Maybe: Another my sister has questions. Addictions do run in families. Is that due to biologic predisposition or bad example? I think both. The worst case is the family member introducing another to the drug, violating trust in a terrible way. If addictions run in your family, i would be extra cautious about even trying any abusable drugs (cocaine, opiates, stimulants , meth etc) even once!

Genetic addiction: As noted by dr liebowitz, it is not known how much of a genetic component there is to addiction. Addiction clearly runs in families and anyone who has a family member addicted to a substance is likely more prone to addiction to that substance. That being said, everyone is addicted to something. Though drug addiction is more dangerous, the behavioral patterns are the same for all addictions.