Dont waste their time or yours. Find a good excuse that you can't be employed by them. If you dont take the test then you wont fail. Call them first and tell them you have found employment elsewhere that suits you better at this time. Be kind, write them a letter telling that they gave you a nice job offer and you appreciate it, but you found something else that suits you better. Make sure to thank them for their time and interest in you as a canidate for employment. Be professional about it. Most companies keep a blacklist of people that have failed pre-employment drug tests. And if you ever apply there again, you will be automatically declined employment. A hair test will find you positive for months after you have used drugs. Again, don't take the test. If you don't take it you can't fail. (I know this from experience). Call em', write them a follow up thank you letter and find someplace else that will hire you without a drug test. You might need that job when you will test clean someday.