It's a qualified “it may”.
When I train officers with approved screening devices, or more likely with approved instruments—and I've trained probably thousands by now—one of our first training things is that if someone has something in their mouth, have them get rid of it and don't take a test for 15 minutes, because you have no idea what the impact of that unknown substance will have on the testing.
It's yet another area with passive devices that we have to investigate.