My brother in law is taking his CDL in a few days. He was purscribed Vicadon for a shoulder injury a few months ago. Latley his shoulder has been bothering him serverly but he doesn't want to take a vicodin for it because he doesn't know how long it stays in your system. If he passes his CDL, he has to have a piss test for drugs. (opietes) So, how long does it last in your system? I need a clear answer please:)

1-3 days depending on his metabolism. It can be as much as 7 days. If he can provide proof of recent prescription then it shouldn't be a problem.

When he takes the drug test they will ask if he has used any prescription drugs, merely say yes and give them the name of the drug taken,
Since you had the drug legally it should not be a problem