There are instant saliva tests that can be administered. The person being tested puts the equivalent to a popsicle stick in their mouth. Keeps it for 10-15 seconds and then gives it to the tester. It shows the results instantly. While they are slightly more expensive then instant urine tests, they are cheaper and quicker then lab tests.
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Also, the lab that does our toxicology tests (urine samples) at work gets us the results in hours. And that is them coming to pick up the test, transport it to their facility that is easily over an hour away and then testing the specimen and getting it online. If an EP wanted to do onsite drug testing, it can be done the day before and have the results for the morning. I am also sure that if the client was big enough the right company would figure out a way to get them the results quicker if necessary. Urine tests conducted by a lab test for more then illicit substances to ensure that what they are testing is actually urine or if the urine was "cleaned". There are always ways around being truthful when rendering the sample, but then possibly supervising the rendering of the sample may be necessary.