All of us have taken drugs at some point in our lives. There are times when we binge on painkillers. Do most people become addicted? Nope. Just because it's a drug, it is not necessary that someone will become addicted to it and not every drug is addictive. Everyone is different, it's not necessary that one person will have the same affinity to a particular drug as someone else. You mentioned caffeine, I know a lot of people who are addicted to coffee (Requiring at least 3 cups a day) while I on the other hand rarely drink it - tried drinking coffee for all nighters and next minute I was sleeping like a log, doesn't work for me booo. I know a lot of people who have done different recreational drugs (molly, LSD, shrooms, and the very common weed quite a number of times) yet none of them became addicts.