Anyone taking any codine or opiate based medication should be aware that this medication will show up on most drug tests as a Postive within a couple of hours of taking the medication on some drug tests. Others may take a couple of hours more. Codine is found in many common over the counter pain killers, and cold and flu meds.
What the routine tests do not show is the concentration. Any positive test is dependant on company procedure, but usually from my experience, the person is stood down on full pay until the sample is sent of for GCMS analysis. There are guidelines stating permitted levels. It would be rare for a single tablet taken a couple of times per day to go over those recommended guidelines, but some companies are much stricter than the guidelines suggest.
Any reading over the limit is dealt with as per company policy and procedure, and can vary from sacking to merely "call in sick for a day or two".
Any pain irritating enough to cause folks to start hunting for the strongest OTC analgesia, could well be irritating enough to be distracting. I am a happy advocate of NSAID's specific to the complaint. Some being better than others. But always read the label and the list of ingredients. Don't double up. If you are "piggy backing" medication to treat a number of symptoms, be aware that many drugs are processed through the liver. By that fact, adding alcohol can cause major changes to breakdown rates, levels of free drug in the blood stream and so on.
If the piece of paper and the packet state, "WARNING - This medication may cause drowsyness", its probably a good indicator it is on the list of substances not recommended for use in an aviation environment.