A near certainty
more than someone with no family history, but don't worry, mental illness isn't so bad. it's not a death sentence or anything. i've had it pretty rough in the past and i'm still optimistic.
If you don't do a bunch of drugs and alcohol then you might not suffer like they did. I would say you may have a one in three chance of dealing with thos things.
It is nice to know that if you do have problems there is lots of understanding out there as to how to treat these problems. Just think when they had no understanding of mental illness and you usually became an alcoholic to stop the pain but it made the pain worse in the process. You live in a time when you can treat any problem like that so relax.