Trust can actually be part of the recovery process
Drug addicts are people, and all people are different. In order for an addict to have the best chance at recovery, it is often essential that their friends and family members trust them.
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Drug addicts are constantly facing the stigma that they cannot be trusted, but this stigma can actually reinforce untrustworthy behavior in them. It can be a difficult path to navigate, but in order to help an addict that wants to change, often the first step must be to trust them. When someone is addicted to drugs, they are not necessarily unable to control themselves all of the time. It is crucial that they feel loved by those who are close to them, and those who are close to them can display their love by showing that they trust them despite their addiction. While it is unrealistic to be completely trusting of a drug addict in all situations, trusting them when it makes sense to do so can go a long way toward helping them recover by making them feel encouraged.  This tactic of showing trust toward drug addicts must be used with discretion; not all drug addicts can be trusted often, and some should not be trusted at all. It is important not to paint drug addicts with a broad brush, though, because every individual is different, and some addicts need to feel that they are worth trusting in order to find the strength to recover.
Drug addicts tend to be willing to go to extreme lengths to support their addiction. Trusting someone in that circumstance and especially letting them know that they will be trusted despite their addiction will likely let them know that they are in a situation that can be taken advantage of. Even if a drug addict appears to be trustworthy, they may simply be lying. A level of distrust will actually improve the situation since trusting them will allow them the opportunity to manipulate the situation in order to support their addiction.