Certain medications can be detected in your system several days after consumption, but the actual medicinally active chemical compound has broken down and no longer is doing anything in the body.
Does the marijuana drug test indicate that the person merely consumed something several days before, i.e. there are metabolites( inactive beakdown products) in the system vs indicating that the drug is still active in the system? There is a world of difference.
The blood runs free, the rain turns red, give me the wine, you keep the bread.