Takes about 2 days. When you do the drug test, you are asked what medications you are on or have taken within so many days. Just tell them you have a prescription for them and when your last dose was. It should have no bearing on if you get the job or not. Basically they are looking to see if you take illegal drugs and drugs you don't have a prescription for.
Best of luck. Hope this helps, If you need anything else please feel free to ask. If you found this helpful don't forget to click the *ACCEPT* button and leave *POSITIVE* feedback.
