PA employment law, can I file an appeal to a denied unemployment claim

You have the right to file an appeal within fifteen days of the decision, however, have you already had a hearing before a referee? Do you have evidence to present? If not, you're going to have a tough time. Incidentally, drug tests reveal more than just what you smoke. If your employer had an established policy that a failed drug test meant termination, it will be difficult for you to overturn the decision.