Is it possible you have the cause and effect backwards? These people could have highly addictive personalities and were just switching from one drug to another and it’s not the actual drug that’s the issue.
Take the adderall and benzodiazepines out of the equation and they might just as well be using cocaine and barbiturates.
Barbituate withdrawal won’t kill you.
Benzodiazepines, and alcohol, can actually induce death if you withdraw too quickly