I have a urine test to take in 20 days. I have a script for Percocet 5/325. I dont take them much. I take 1, 20mg OC in the a.m. and 1 20mg OC in the p.m. The drug test is for a pain management clinic, so its ok to test positive for the Percocets. My question is, can they tell that I have been taking Oxycontin instead of the Percocet, just by the urine test results? If so, how long before I have to take the test should I stop taking the Oxy's, and take just the Percocet?