Drug screening at clinical

I was wondering if any nursing students had a separate drug test/screen at their clinical sites. We of course had to submit a drug test prior to the start of the program, but I was reading through the student handbook/student participation agreement and waiver for my specific clinical location and there’s a document we have to sign about drug screening. It asks for our prescribed medications and talks about the legal rights they have regarding our drug tests after we sign the agreement. I don’t have a problem with having another drug screen done at my clinical setting at all, except for wasting time during clinical. I’m wondering if these documents are referring to the drug test we already completed that was sent to our school, and if this is just a release of information and consent. Any ideas? I don’t really care either way but I didn’t want to email any of my professors asking about it when it’s not a problem. I’m just curious. TIA