Questions about False Positives in Drug Testing, page 280

False Positives Forum

This forum is intended to help those who Do NOT Abuse Drugs. We do NOT support the illegal use of any substance. If you have experience with false positives, share your experience. What would you tell someone about drug testing and false positives? Please remember that this forum is not for medical or legal advice.

False positive for cocaine
Date: 3/25/2013
I’m on probation and have to take urine drug tests (I’m not on probation for drugs). I take elavasil, ritalin and indomethacin. When I go in and test, one day I’m positive for cocaine the next time I’m not. I swear I’m not doing anything, I just don’t understand. I even went and had a blood test done to prove I was telling the truth, which came back negative for everything.


AskDocWeb: Please see False Positives for Cocaine.

Test came up dirty
Date: 3/25/2013
I got a posative test for benzoarazapines and i take melatonin and prozac everyday…i havnt even heard of the drug and i need an answer as to why it came up dirty for that?


AskDocWeb: Prozac has shown up as false positives for amphetamines and LSD (References: 31 and 47) but not benzos. Melatonin does not show up on urine tests for drugs of abuse. You might check the big list to see if something else you might be taking is causing the problem.

Worried about background check
Date: 3/25/2013
I recently had a GC-MS hair test performed on me. It came back positive for opiates and cocaine. I do not recreationally use any drugs, have never touched cocaine and was very surprised about these results. I then remembered that I had a tooth pulled 4 months prior and was given vicodin for the pain. During the surgery I was given multiple doses of Lidocaine as well as laughing gas. I figured that the vicodin caused the opiates and the lidocaine caused the cocaine. My dentist sent in my file and after review the testing facility said that the opiate “charge” was cleared because of the prescription however the cocaine was not cleared.

I have never done cocaine and am really at a loss of what to do. In the test I had 7.8 nanograms per 10ml and the allowable amount was 5.0 nanograms per 10 ml for the metabolite of cocaine. I was sick about a month prior to the test and took azithromycin “Z-pack” 6 pills to get rid of my cold. Could that have caused this false positive?

The job offer was revoked and now I am worried about my background check and how this will look on my record. Any assistance is greatly appreciated and I look forward to hearing from you. Sincerely,


AskDocWeb: Azithromycin has never been documented in any published medical study to cause a false positive on urine drug tests. If readers have any suggestions for Ryan, feel free to speak up.

False negative
Date: 3/25/2013
My husband has MS. He is working with his Neurologist to find a non narcotic solution to his pain management. However right now Norco helps for his bad times. He gets the 5/325. He recently went it for some blood work and a urine test and they made him come back for a second urine test. Both time he fasted so he did not take his pills before going. He takes about 2 a day pretty regularly. He was just told by his doctor that he can no longer get a Rx for it because it was not detected in his urine test and they think he is selling it. That is not the case. He is a pretty big guy @ 320lbs. He takes blood pressure pills too. Is there anything that could be causing this to happen?

Concerned wife

AskDocWeb: Urine screening is not an exact science and there are a number of possible reasons that a prescription might not show up:

  • The drug was not taken as prescribed.
  • Drinking an unusually large amount of water can dilute a test sample below the amount needed to show on a drug test.
  • Some people metabolize drugs exceptionally fast and if the last dose was taken too long ago it might not show up.
  • A small percentage of drug tests are faulty.
  • If the drug you are taking has a very short half-life and if the last dose was taken too long ago it might not show up.
  • The cutoff level for positive on the test may be unintentionally (or ignorantly) higher than what is intended, therefore a negative result is being detected. If this is the case then the patient may be positive, just not positive enough to register on that particular test.

It may help to explain to your doctor that you want to do whatever you can to resolve this matter and make certain they understand you are distraught over this. Ask if they would do a blood test or hair shaft test and use the results to declare your urine test as incorrect. A blood test will show what is currently in the body and a hair shaft test can show that you have taken your meds in the past ninety days. Either test may be a good choice for those who have false negatives to prove their innocence.

Officer in trouble
Date: 3/25/2013
Epinephrine=Meth? Help! bee sting so i used my epi-pen, it showed up as meth. I’m a 50yr old police officer, and I also take 200mg of Doxycycline a day and 100mg of Doxepin. Could these combine to make for a positive meth reading in urine?


AskDocWeb: The Doxycycline should not be a problem. Although Doxepin has been reported to sometimes show up as a false positive for LSD (References: 36 and 47) or for tricyclic antidepressants (References: 33 and 52), it does not show up as meth.

Epinephrine has not been documented to show up as meth however, a number of allergy medication are known to do that. Unfortunately the specific drug in those allergy meds that causes this has not been identified.

Join the army?
Date: 3/26/2013
Can you join the army if you are prescribed dexamphetimine??


AskDocWeb: We don’t know the answer to that but if you call up your local recruiter I’m sure they would be able to explain your options. The military services, especially the Air Force, are known to use “go-pills” or performance enhancing drugs but that use is confined to specifically defined situations. (See

Date: 3/26/2013
will cimetidine show up on a drug test?


AskDocWeb: Not on a urine test for drugs of abuse. Cimetidine (Tagamet) is in the class of drugs called H2-receptor antagonists, which are used to treat:

  • Benign tumors of the hormone producing glands
  • Conditions in which stomach acid is pushed into the esophagus
  • Excessive production of stomach acid
  • Heartburn
  • Increased stomach acid from systemic mastocytosis
  • Stomach ulcer
  • Ulcer of the duodenum
  • Zollinger-Ellison Syndrome

The oral form of Cimetidine may also be used to treat stress ulcer prevention, pancreas organ failure, bleeding from stomach, esophagus or duodenum, hives, stomach ulcer caused by aspirin or Ibuprofen-like drugs.

Clairil Hair Color
Date: 3/26/2013
Can Clairil Hair Color produce a false positive in a car breathylizer?


AskDocWeb: We haven’t seen a product called Clairil Hair Color. Maybe you meant Clairol Hair Color. If so there are many products in their hair coloring line. None have been reported to cause any problems with urine drug tests.

E-cigarette blu cig
Date: 3/27/2013
I recently screened positive for MDMA on a urine screen, I have sent the sample away for confirmatory testing. The only change I have made since my previous negative screens is the use of an e-cigarette (specifically the blu cig) … would this cause a false positive for MDMA?


AskDocWeb: To date there is no record of e-cigarettes causing a false positive on urine tests for drugs of abuse.

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