The fakes are so good now, it is almost impossible to tell. I buy urine fent test strips online and they work to test the pills. Flake off a little of the pill with a knife or something sharp and dissolve in a small amount of water (about 2-3 tablespoons) and then test with a fentanyl urine test strip. If there is any fent in them, it will test positive. Remember, most of these test strips are negative when there is 2 lines and positive when there is only one line. If the second line is light but there, it is still negative, but if there is only a control line and nothing in the test line, it is positive. The opposite of a pregnancy test. I have used this method for a couple years now and have got a positive every single time on the fakes. Hope this helps.