You may have a friend -or enemy, that added a little snort to a friendly drink.
No. They are only looking for specific substances. If it's prescription based suppressant such as an amphetemine, you may need to show that you have one. When I took a drug test for my job I told them that I was taking an ephedra based supplement (when it was legal) and that wasn't a problem. They do ask you if you ate poppy seeds, because since heroine comes from poppy seeds it may show a false positive.