There are all sorts of different times as to when you should conduct DFW drug testing. Knowing when will make it easier for you to strengthen your testing program la420doctor It will also allow you to learn more about your employees, even before you bring them on board. Pre-Employment You will definitely want to have drug testing in DFW conducted prior to employment. This will allow you to see if candidates are using drugs in any capacity. You dont want to offer employment to someone if they test pos.