Heroin isn't significantly more addictive than cigarettes.

You can also easily overdose from nicotine, its just that this is mitigated by the relatively slow delivery mechanism, which makes it so that you get terribly sick before you could consume lethal quantities.

If we can come up with an effective delivery method then heroin would be no more dangerous than cigarettes (sort of, you still can't, for example, drive on heroin, but also it doesn't destroy your body long term).

Perhaps heroin could be adultrated with a chemical that causes nausea when consumed in an amount proportional to a dangerous level of heroin. This would help heroin users build the same negative associations with high doses that cigarette smokers do, and could make them unable to consume more.