they sell hair cleanser that strips the protein out of your hair(supposedly) so you can pass a test, but the newer hair test can detect it and it will come up as adulterated. as a hairdressers kid lol, i can tell you that the average hair grows at 1/2 inch down to 1/10 inch per month depending on age, diet, etc. that means every inch of hair is anywhere from 2 to 10 months of your life. supposedly, they are oly supposed to go back 18 months from the folicle in a hair test , which is relative to how fast your hair grows so that becomes indistiguishable. so the only effective and confident way would be to shave and not imbibe anything you wouldnt want them to find in a hair sample. a test for confirmation before you submitted a sample, like the gentleman said before me , would give you the peace of mind and confidence for the hiring process