Hi: Hair tests are considered pretty accurate as the length of the hair has a lot to do with historical information. You are correct in stating that certain meds can trigger a positive response. What you need to do to completely clear your name is repeat the hair sample test and at the same time have the blood testing done and sent to a licensed lab that does drug testing. You have to pay out of pocket. Ask them just to check the blood for cocaine because that is all you have been told about and should make it cheaper than testing for everything. By doing both samples at the same time you are removing any doubt from anyone s mind. If you were to go for the blood test today, the previous hair test would still be considered positive. Most employers will not pay for the blood test. Once you test positive, they will not hire you. You will also want your doctor to verify in writing that you have allergies and what medicine you took. Good luck, Carol Rogala D.O.