Can a drug test tell the difference between percocet and vicodin?

[juswondering]

My friend is taking percocet for his back.He ran out of percocet and bought some vicodin from one of our friends.He took a vicodin before his appointment (and all day before) and they tested him.The test came back that he had NO percocet in his system.Do they really have a test to determine you have specifically percocet in his body??If they do...seems very expensive.I just thought they test for the general ones likepiate,cocaine,thc,etc.

 

[20 Year Nurse]

Percocet and Vicodin would both test a simple positive in the opiate category on a drug test.