You have touched on a very significant aspect of an opioid's sabotage of the brain. New research has isolated one aspect of the biochemical effects: reduced loss aversion. This chemically induced pathway alteration creates decision-making deficits that result in a dramatic lack of judgment and a dramatically reduced concern for the consequences of ones actions. This action in itself facilitates the user’s decision to maintain their habit even when they are aware of the most negative consequences. This deficit causes a series of other complications: impaired self-control, impaired impulse control, the inability to plan for the future and long term memory loss. With these findings, it mystifies me why that information is not out and the drums to rid these biochemical poisons from society are not played.
Unless the drugs are prescribed (which is a whole different conversation) that decision has to be to engage in an illegal activity to obtain the item upon which they are fixated. You have to locate a criminal and do 'business" with him, knowingly. It's not like "here it is, will I take it or not take it?".
Then (aside from prescribed drugs), what makes the "victim" take a needle in the arm the first time? If they avoid the first "hit" they'll never be addicted.