Mott the Hoople
Sweet Jane
Depends on how you do it. You can forget about doing hair sampling as even the prescreening assays are costly and positive tests must be validated on a GC/MS...which is very costly. ELISA assays work well for screening but are prone to false positives (and false negatives) and still must confirm positive results with GC/MS validation, which again, is costly.
Screening of this nature is mostly a waste of money as it really only works in a random sampling where the individual to be tested does not know when and where they will be sampled. As most drugs are water soluble they are metabolized rapidly be the liver and person, generally speaking, will only be caught if they have used the drug recently. Pot is a noted exception t-delta THC is lipid soluble and can stay in fatty cells for a significant time and this can be a problem for chronic users. Opiates also have longer half lives and, due to their addictive nature, can be an issue too but ELISA screening tests have very limited sensitivities and can be defeated by dilution. That is the person takes a diuretic or drink a large volume of water prior to sampling. So the fact that the individual knows there is a likely hood of their being sampled and tested makes these ELISA screening tests easy to beat. I know, cause I used to administer drug testing for a company I worked for.
My point being, that unless you're willing to commit to a high degree of cost by using highly sensitive methods like GC/MS most ELISA based drug screening programs are ineffective as you cannot really randomize sampling. If you abstain for a day or two prior and dilute your urine via a diuretic or hyperhydrating more than likely you will pass a standard ELISA drug screening test.
Which brings us back to, well if this is well known in the state of the art, they why waste money doing it? Well the political reasons are obvious. You can demonize the poor.