You should start by reviewing your police handbook and keep it handy in case you need to hire an attorney. Also get a medical report from the doctor that prescribes this medication, completely describing the necessity, affects and how the results will show up on such a drug test. Good luck.
Please be advised my answers to questions does not constitute legal advise and you should not rely on it, due to the fact that we have never met, I have not been aprised of the facts in you case nor have I reviewed any documents.
When you get called in for a random drug test you are given a medication form on which you list all the prescription medications, over the counter medications and supplements you take. You seal the form and turn it in with your sample. If you test positive the medical examiner's office opens the sealed form. If you put the medication on the form that you tested positive for then the medical examiner's office reports it to your department as a negative test. If you did not put the medication on the form it will be reported to your department as a positive test. Most departments then require that you produce documentation from your doctor that the medication was prescribed to you and proof from the pharmacy that you filled a prescription for that medication before the test date. If you have any further questions please contact me at firstname.lastname@example.org
This answer is provided for informational purposes only and does not constitute legal advice or create an attorney client relationship.