The addict is not the only one affected by symptoms of addiction. There are clear signs that the general population around them, the general population who think about them, feel the torment that is created by that addiction.
Other devastating behaviour can also be caused by addiction to both (to themselves and others).
The meaningful relationships of the addict will eventually erode due to this slippery slope making it harder to recover. This arrangement is about those individuals who are influenced in the life of someone who is addicted.
It comes naturally that a friend always relate himself/herself to his/her friend. Sadly, this simple behavioural observance leads to a more harmful situation and often ends with full-blown addiction. Peer pressure makes addiction a more potent social contagion.
Being shun by your sober friends, you tend to hang around with your new clique having the same habits as yourself. Unfortunately, for an addict in this situation, the new group of friends may develop from drug abuse bad habits.
New friends may be a part of the drug culture that made you addicted in the first place, which would be devastating for recovery, as it makes it much more hard to create new, more meaningful relationships that could actually help you.