So, I was at a party with some friends and decided to take a couple pills (not sure if we are allowed to put drugs on here so I'm just going to play it safe). The next morning i was eating breakfast when my friends tells me she needs the morning after pill and asks if I will go with her. So, naturally, I said of course and we went to the chemist to get one. The man giving it to her said it was procedure that if you're getting the pill under 25, you do a Chlamydia test. He then turns to me and asks if I want one and I said no. He kept on asking and was telling me all of these side affects and how there is a high chance I have it. So in the end I got so scared I just said yes. However, since then, I've been really scared the drugs will show up.
I understand that this is me probably being paranoid and even if they did find it, what would they do? Most likely nothing at all but still, my anxiety really won't listen to my logic on this one (not that it normally does anyway).
The simplest (cheapest!) is like a modern pregnancy test. In both cases, you coat the base of a strip of porous material with monoclonal antibodies capable of binding to what you're looking for: the hormone HCG for a pregnancy test, assorted strains of Chlamydia here. Each antibody has a coloured particle attached. If what you're looking for is in the urine, it'll attach to the antibodies and they will be drawn up the strip along with the urine. Result, a coloured line at the top.
They don't attach to anything else, or the tests wouldn't work - a pregnancy test is no use if it gives a positive result just because the user has taken some E or whatever.
You can get multi-test strips, some of which test for an impressive variety of things at once but they cost more and if you didn't consent to other testing, it shouldn't happen in any form that could be linked to you.