No Drug Tests For Charlie Sheen and Brooke Mueller

As TMZ first reported ... Brooke was photographed last week holding what appeared to be a crack pipe. And there are other problematic images as well -- like the one recently in Hawaii, when Brooke walked up to a parked car in a seedy area with cash in hand.

The two rehab veterans each have selfish reasons to avoid drug testing, but Brooke is especially worrisome because she is the primary caregiver of the twins. Although Brooke's parents step in when she goes to rehab -- and she goes a lot -- Brooke ultimately calls the shots.