Tests for LE do not determine levels only presence, regardless of the substance the suspect is under the influence of(with the exception of alcohol)! And once again, with a VALID PRESCRIPTION, it is LEGAL to drive while taking pain meds. Of course, many times a great deal of people could be arrested for violating the STUPID LAW because they get hopped-up on prescription meds and then drive(possibly hurting someone because their judgement is impaired), but there is no such STUPID LAW, so people must use their common sense. LE only needs to show a trace or presence of an illegal substances in a persons system, because the substances are in fact, ILLEGAL! So, it really doesn't matter how much is in your system. You could ingest 5 pounds or 5 milligrams and the bottom line is still the same, it is an illegal substance in your system, regardless of the amount and you will be prosecuted if it is detected.