This is a tough question. The answer to your question is, both. You will get asked about why you did poorly in school the first time, and you will need to have an answer to that. It may be hard to explain your record without mentioning it, and if you don't give a good reason for the gap in your history, people tend to assume the worst (prison, insane asylum, you get my drift).
However, you will also likely run into resistance if you have a known history of substance abuse, and understandably so. Physicians with substance abuse problems are put into positions of serious temptation, particularly if they go into certain high risk specialties like anesthesiology or emergency medicine where they're handling controlled substances. Anesthesiology is especially high risk; a few anesthesiologists (and nurse anesthetists) die every year from overdoses. So if you are going to be up front about your past, I suggest that you also show insight into this issue and go on record as planning to avoid specialties that give you ready access to controlled substances.
Please note that I'm not merely suggesting what you should say to adcoms; anyone with a history of substance abuse truly should not go into anesthesiology for their own safety and for the sake of maintaining their sobriety. Hopefully that wasn't your dream specialty....