Hi there ~
I understand your concerns. I believe that you need to consult a psychiatrist
who is experienced in the treatment of drug and substances. If you need to make sure that you are negative for drugs a serum tox screen is recommended and if you are trying to escape the test it is a problem that needs psychiatric attention. I hope you understand as I am not trying to not answer your question, but to actually try to get yourself help that will benefit in the long run.
I hope this helps. Take care of yourself and have a lovely day!