Most definitely a (former) drug addict - here is the thing... medical school is hard. I mean - HARD. Competitive. It takes a strong character to get through those 6 years (where I'm from, it lasts that long)... I mean, you know the pressure. You know it gets ugly. Can you really count on a former drug addict to have what it needs to work through that pressure without relapsing...?
A dropout has proven, by dropping out, that they don't have the commitment/school abilty to go through it. And just like that, a drug addict has proven, by being a drug addict, that they don't have the character it takes to go through life challenges without looking for an unhealthy ways of coping. And medical school is full of challenges. It's full of free access to various drugs, too.
Personally - I'd always take a dropout before a drug addict, if I had to choose. For one reason: I believe it's easier to improve your school abilty and motivation than your addictive personality. Normally - I'd ban both from even applying.
I'm just genuinely shocked to learn that the deadliest mistake in the States (I'm European) medicine world is... well, giving up. I always thought the rules on crimes, drugs and especially cheating are much stricter.
I hope I didn't offend anybody, I applaud everyone who managed to get off drugs and stay sober, that takes a lot of hard work.