Drugs in prison

My LO has a cellmate who is deep in drugs (and in debt), which is unfortunate. My LO has been doing a good job of saying no, especially since they’ve already been raided and UA’d. Now his cellmate is saying he got “stuff that doesn’t show up on the UA” because he’s a bad influence and I’m sure wants him to do stuff with him. What drug wouldn’t show up on the UAs? I’m just curious.

Also has anyone ever had their LO complain/report issues and get moved? He needs a better cellmate 😮‍💨