I have not read any articles recently about urine drug tests, so I thought I might discuss it here. A useful article with many excellent references was written by Karen Moeller, in the Mayo Clinic Proceedings: www.mayoclinicproceedings.com/content/83/1/66.full. If you are an old-timer such as myself, you probably remember the Yippie Handbook: "Steal This Urine Test".
The problem for the tester is the existence of false negative tests, and of course the problem for the testee is false positive tests. As a compromise, all tests have a cutoff, above which the test is considered positive. The urine tests are almost always a screen by immunoassay for either the parent drug or a metabolite. Since, as we shall see, many OTC as well as Rx drugs can give a false positive for various "drugs of abuse" (a technical term comprising amphetamines, cannabinoids, opiates, cocaine, and phencyclidine), for legal purposes any positive screening urine drug tests must be confirmed by gas chromatography-mass spectroscopy. The immuno screening test is used because it is rapid, not labor intensive, and cheap, much in the same way that the VDRL test is used to screen for syphilis, and the FTA to confirm it. As an example of the problem with a false positive screening test, since Lyme Disease is caused by a spirochete, just as syphilis is, many patients with Lyme disease will test positive on a blood screening test for syphilis.
One immediate problem occurs with the amphetamine assay. There are 2 chiral isomers of methamphetamine: d-methamphetamine and l-methamphetamine. The (d) and (l) prefixes stand for (dextro) and (levo) respectively. The d-isomer if dissolved in water will rotate the plane of polarization of polarized light to the Right, and the l-isomer will rotate it to the Left. Louis Pasteur showed over 100 years ago that (almost always) chemical syntheses make an equal amount of the (d) and (l) isomer, but animal enzymes will usually act on one and not the other (he used tartaric acid for this demonstration). Thus your body usually uses only d-sugar isomers (hence dextrose), and the 8 essential amino acids for protein synthesis are all l-isomers. In fact if you were fed only d-amino acids by IV, you would starve to death.
Now even gas chromatography is not sensitive enough to distinguish between d-methamphetamine and l-amphetamine. The d-isomer works as a CNS stimulant and produces euphoria, and the l-isomer produces peripheral vasoconstriction, and thereby relieves cold symptoms. Of course the OTC drugs used for cold symptomd such as pseudoephedrine, phenylephrine, and phenylpropanolamine will produce false positive tests. Most stimulant drugs used for ADD (such as Ritalin) and most diet drugs (such as phentermine) will also produce a false positive test. More amazingly, the following are some of the Rx drugs that will give a false positive methamphetamine urine screening test: Amantadine (used for the flu and for Parkinson's Disease), Wellbutrin (buproprion), Zantac (ranitidine), Trazodone, Desipramine, Trimipramine, Labetolol (for blood pressure), Chlorpromazine, and Isoxsuprine.
False positive tests for cannabinoids (marijuana metabolites) can be produced by Efavirenz (an anti-viral used to treat AIDS patients), ANY of the NSAIDS ( Motrin, Alleve, Celebrex, etc.), Tolmetin, and any of the proton-pump inhibitors (Nexium, Prevacid, omeprazole, etc.).
False positive tests for phencyclidine ("Angel Dust") can be produced by Effexor (venlafaxine), Tramadol,, Advil/Motrin/Ibuprofen, Robitussin DM (dextromethorphan), Benadryl (diphenhydramine), Doxylamine, Imipramine, and Ketamine.
False positive tests for opiates: Robitussin DM (again!), Benadryl (also again), poppy seeds, quinine, Rifampin (used to treat TB, and also occasionally added to the Rx for severe staph infections), and ALL of the quinolones (Cipro, Levaquin, etc.).
As far as is known, no OTC or Rx drug produces a false positive test for cocaine, unless the Rx itself contains cocaine.
For completeness, I should add the length of time that drugs of abuse can be detected in the urine:
Amphetamine---48 hrs., Barbiturates----short acting---24 hrs, long acting (e.g. phenobarb)---3 weeks, benzodiazepams-----short acting (e.g. Ativan/lorazepam)---3 days, long acting (Valium/diazepam)---30 days(!), cocaine metabolites----2 to 4 days, Phencyclidine---8 days, Marijuana---once---3 days, 4 x a week---5-7 days, daily use---10-15 days, long term heavy smoker---more than 30 days.
I should also mention that some urine tests also use indirect testing methods, such as testing for the presence of a diuretic, which was taken by the testee in order to dilute his/her urine and cause a false positive test. If your company wants to see if you are a smoker, they will test your urine for the presence of cotinine, a metabolite of nicotine. Unfortunately, many vegetables such as tomatoes contain a high concentration of cotinine naturally, so if you are a true vegan, you may have a "true" false positive test for tobacco use, in the sense that the chemical is really in your urine, but was only derived from your diet.
BTW, the ingestion of ethyl alcohol will produce a positive urine test for 7-12 hours.