Depending on the test you could pass with ephedrine in your system. High levels of ephedrine can result in false positives for amphetamines in some tests. If that does happen some labs will, for a cost, do further, more extensive testing methods, to confirm amphetamines or not. I believe 72 hours should be enough for ephedrine to clear your system completely. If it is important to you then you should do what is needed to pass.