This came in with the crackdown on drugs, narcotics specifically.... the closing of pain clinics and the farming out of patients to government approved facilities.

EVERYONE has to have urine tests periodically if they are taking certain meds.

IF you are on the up and up with taking the medicine as prescribed and not taking anything not prescribed, it's not going to harm you. (Other than the breech of privacy that the Constitution says we have!)

They can verify that you are taking the drug...and not selling it.
They can verify that you are not taking non-prescribed drugs to augment your reality.
They can help analyze how much of the med is being used by the body (they ask when you last took some and how much, right?) and if you say you need more, the urine can help them realize that you might just need a different dosing.

The government makes them do this. It's a hassle to say the least. I would rather do the urine test than the mouth swab thingy... it stays in your mouth until it has enough saliva to register the drug level...but my mouth dries up and I can't even swallow and then I can't talk and then I can't breathe because the whole way is dried! UGH.