It's not just about the alcohol or drug which lessen impulse control. Hate to say it but 'the party' or 'feeling high or buzzed' could've been a long standing desire before they became 'addicted'. In other words their own gratification always had priority but becomes more pronounced when they are addicted.
As noted selfishness is one of the issues. Selfish is selfish intoxicated or sober. If one is only worried about themselves above and beyond their basic survival there's not much one can do other than keep yourself and others safe. Stay out of their way and lives. Their consequences are for them to endure. Not yours or their kids.