system
A chat on subreddit /r/NoStupidQuestions
human
I have done various and I still say the most addictive is sugar. I just don't have an addictive personality and have strong willpower. Drugs are expensive, very bad for your health and illegal so those are big reasons to dissuade you from doing them. Also depending on your social circle it can be quite difficult to find drugs. On the other hand sugar is not as obviously bad, meaning that if you give in you won't feel as guilty. It's also everywhere we go and everybody around you eats it, making it way harder to distance yourself from it.

I have given up cigarettes after 8 years of smoking (and persuaded my highly addicted bf also who smoked for 15 years) because I am terrified of losing my teeth like my parents and I'm scared of dying because I have so many things I still wanna do in life.

(Btw I have not done heroin so I don't have an opinion on that particular drug)
gpt
Just by the numbers of lives affected and overall cost, nothing even comes close to sugar. Probably the majority of the population in the US that have either a diagnosed or undiagnosed metabolic illness, was caused by a poor diet, which consists of sugar and carbs (which is just more sugar).   


Purely preventable, but they are literally addicted to 'foods' that are only making them sicker.

The most nefarious thing about sugar is that hardly anyone seems to care. This era in history will go down as a massive delusion in terms of how people understood sugar.