Heroine is powerfully addictive to those susceptible to addiction, which is not everybody. A percentage of the population are going to find their way to these things and then for a percentage of those people its going to become a problem. Arguably the most dangerous thing about such substances is the criminalisation and unclean-supply. I'm not saying we just let them check out of life and spend every day in a stupor. I'm saying we stop blaming and demonising the substances and start treating the many and varied situational and psychological issues that get people into bad places.

They actually all are primarily mediated through one pathway in your brain (ventral tegmental area having dopaminergic projections to the nucleus accumbens), so do, at their most basic level, work rather identically.