I was fired from my job of 9 1/2 years for failing a UA, what should or shouldn’tI tell a prospective employer when asked whyI left?

What you should or should not tell a prospective employer is really not for anyone here to tell you.  A lawyer is obligated to advise you that you must always tell the truth.   What we can tell you is that many states have reference check immunity laws, meaning that an employer is offered protection when providing a job reference for someone. So if the prospective employer calls and asks "why" your old employer may or may not be able to tell them exactly "why."  Many employers will limit their conversation to your duties or position in their company.  If your state does not have an immunity law it is for fear of a lawsuit based upon retailiation or possibly defamation from their ex-employee.  If the sole reason you were fireed was the failing of the UA and it had nothing to do with job performance then I would call your old boss and speak with him or her about the reference issue.  It is the truth to say that your leaving the company had nothing to do with your job performance but rather other issues that you may not wish to discuss.  That may send up a red flag.  Seek help from an employment counselor in your area on the way to put a positive spin on the matter.   Good luck.