How did you come by this information? I don't recall Zac saying all of this on the show. I thought the brain tumor was when he was around 19 or so. He got addicted to pain killers after that, which if you have an addictive type personality, is very easy to do. My neighbor was early 20s and sustained a fall down an outside metal staircase injuring his back badly. He got addicted to the painkillers but in his family his uncle was an alcoholic and his dad abused crack cocaine, so it wasn't a surprise when the kid got addicted.
I had a total knee replacement a few years back. They sent me home with 80 oxycontin pills, which shocked me. I found they didn't really alleviate the pain all that much and they were super constipating. I have about 60 still left. I have often wondered why some get addicted and others don't and I truly do think some folks have an addictive type personality, through no fault of their own..
Also, I just seemed to get a vibe from both of Zac's parents that they like to imbibe just a wee bit too much. We have seen other parents with wine glasses in hand, but it was just a feeling I get from having been around people who like to say they are social drinkers but can't really go a day without having a cocktail. I guess my own biases are showing b/c while my folks imbibed on occasion at social functions, daily drinking was not something they ever did.
I could be way off base but his folks just struck me as big time boozers, which would reinforce my theory as to why Zac became so easily addicted. I thought Zac was sober for almost 10 years, which is a significant amount of time.