At what point is an intervention acceptable? Necessary?

a close friend is not in the best shape – he chain smokes, lives in literal filth, consumes alcohol constantly and hard drugs pretty regularly, barely can keep his job. he is still pleasant to be around and kind/considerate to a degree, but i know he has great potential that has yet to actually manifest itself. but then again he is only 24. am i being too square?
recently my best friend handed him a job that basically would pay him to do what he loves to do – and it would showcase his work to important people. how often does that happen? he committed to it and then flaked out last minute to do drugs with friends.
i get it – he’s young and this is brooklyn… but at some point i feel like it’s just not ok.
should i do something? what?