What Causes False Positive Drug Test Result For Phenobarbital?

Posted on Thu, 21 May 2015

Medically reviewed by Ask A Doctor - 24x7 Medical Review Team

Thu, 21 May 2015 Answered on

Thu, 11 Jun 2015 Last reviewed on

Question : I had positive drug test for Phenobarbital. Its realted to a ongoing DWI case. I spoke with my attorney and he asked me about it. I took prescribed Xanex before a flight and had a mixed drink prior to the flight. The flight got canceled. I rented a car for a short drive to the hotel and got pulled over. That was all I had. I do take Lexapro and blood pressure, diabetes, and cholestoral meds. Can this cause a false positive? They want to prosecute me because of the level of the the Phenobarbital not the Xanex. I don't get it please help!!

Answered by Dr. Bonnie Berger-Durnbaugh (2 hours later)

Brief Answer:
Names of other medications please.

Detailed Answer:
As you probably know, some ingested substances can give false positives for controlled or illegal drugs. For example eating food with XXXXXXX seeds can make a test positive for opiates.

Can you please list all of your meds including blood pressure, diabetes, and cholesterol meds? Did you use any nasal sprays or can you recall what you ate prior to the Phenobarb test? Also, was this a urine test?

I'll see what I can find out for you.

Also, please check the Xanax bottle and make sure that what was dispensed to use is Xanax (pharmacy accidents have been known to happen).

I'll await further information from you and then do some research.

Above answer was peer-reviewed by : Dr. Shanthi.E

Follow up: Dr. Bonnie Berger-Durnbaugh (6 hours later)

Here is what I was taking at the time(this is from the pharmacy):
05/16/14 0000 ESCITALOPRAM 20 MG 30
05/16/14 0000 BYSTOLIC 20 MG 30
05/19/14 0000 ALPRAZOLAM 0.25 MG 20
05/29/14 0000 ALLOPURINOL 300 MG 30
05/29/14 0000 ATORVASTATIN 20 MG 30

Answered by Dr. Bonnie Berger-Durnbaugh (10 hours later)

Brief Answer:
Consider having test sent for confirmation

Detailed Answer:

I did some looking up of medications that can make urine drug screens positive for phenobarbital. None of the meds you listed showed up as doing this. However, apparently standard urine drug screens can have cross reactivities and other errors. So you may want to demand that the sample be sent for retesting via a test called LC/MS/MS. It stands for "Liquid Chromatography-Triple Quadrupole Mass Spectrometry". This is a much more accurate test. I found a lab that does this technique - here is a link:http://www.pcls.com/testing/toxicology/urine-drug-testing/ I don't know what the costs run.

I hope this information helps. Please let me know if I can help further.

Above answer was peer-reviewed by : Dr. Vinay Bhardwaj

Follow up: Dr. Bonnie Berger-Durnbaugh (24 minutes later)

It was a blood test and I believe it was the ms test. I don't know why to think. All I know is that I didn't take anything like that. I'll get with my attorney and see if he can do something else

Thank you

Answered by Dr. Bonnie Berger-Durnbaugh (7 minutes later)

Brief Answer:
Good luck to you.

Detailed Answer:
I am sorry you are having to deal with this. I too don't know what to think if
LC-MS-MS testing was used.

I wish you the best. If there is nothing further I can help with please go ahead and close the communication.

Best regards to you.

Above answer was peer-reviewed by : Dr. Yogesh D