It would be easier to list b5 actors without drug or alcohol issues.
I know that some of them, indeed, died due to substance abuse issues; I don't know the circumstances of all of them. They will all be greatly missed.
Too many others of the main cast had died relatively young, of "natural causes" though. Richard Biggs, Mira Furlan and Stephen Furst stand out.
My impression is that there's not much causation from being an actor to mental fragility. It's the other way around; the pool of people who make good actors is already prone to mental fragility before they become actors.
It is of profound significance.
https://www.amazon.com/Cure-Alcoholism-Willpower-Abstinence-...