For a drug addict, getting the drug becomes the single most powerful motivator in their life.
This is A. True.
Drug addicts bypass those things that they would usually take pleasure in, so that they can get more drugs. People in great relationships (married, with kids, etc.) "abandon" their kids so that they can get their hands on drugs. It is important to understand that they are addicted, so it is extremely hard for them to stop using drugs, but yes, it takes over their life.