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Family Physician
Family Physician, Board Certified MRO
Category: Drug Testing
Satisfied Customers: 12816
Experience:  Medical Review Officer - Physician Trained and certified in drug test interpretation
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I recently had a urine drug screen with a positive cocaine

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I recently had a urine drug screen with a positive cocaine result. I have never used cocaine in my life!! I learned this weeks after my PCP received the results & "dismissed" me from her practice when i called to make an appointment and she refused to see me to discuss the test. I have been an LPN for 15 years and live in a small rural community where despite privacy laws gossip is rampant and can ruin my reputation as a well respected medical professional. I have done some research and possible causes for the positive result. When my urine was collected i was taking amoxicillin 500mg tid for dental, I wear Lidoderm patches(1 on each knee) everyday for arthritis, and i also drink 3-4 cups coffee in the am and approx 1/2 gallon (sometimes more) of iced tea daily. Could this be the cause of the false positive cocaine result? Is there any way to prove it?

There are several issues to consider in this situation. Yes, it is possible that these medicines could cause a false positive for cocaine. The amoxicillin has been reported to cause a false positive urine drug screen for cocaine. There also are many false positive results on drug screens for which the cause cannot be identified. The general recommendation is that any positive urine drug screen should be confirmed by a more specific test, such as gas chromatography/mass spectrometry (GC/MS). The GC/MS will be able to differentiate a true positive from a false positive, although it will not identify the cause of the false positive. The only way to prove it at this point is to request that the specimen that had a positive urine drug screen be further tested by GC/MS. Unfortunately, the urine specimen would have had to be saved to be able to be tested. If the urine is discarded, you can request that another test be performed, but the doctor may be hesitant to consider that a repeat test is meaningful, as the person could have simply quit using after the initial test to yield a subsequent negative test. The other option would be to ask the doctor to perform a hair follicle drug test, which will look back for 90 days, so will cover the period during which it is thought that you used cocaine.


As a MRO, I would have to disagree with the other expert. Amoxicillin DOES NOT cause false positives for cocaine.

Failure of amoxicillin to produce false-positive urine screens for cocaine metabolite.
Customer: replied 6 years ago.
Relist: Answer quality.
This answer gives me no additioal information, actually less information than i found doing(free) research on my own.
I'm sorry that the initial answer that you got was not helpful.

As a board certified Medical Review Officer, I deal with these issues on a daily basis.

Cocaine drug test are actually one of the most specific tests that we have. There really are no over-the-counter or prescriptions medications that cause false positives for cocaine.

Amoxicillin, Lidoderm, coffee and tea would NOT cause a false positive drug test based on any scientific evidence.

The only scientifically valid explanations would be use of cocaine (this could be related to a recent ENT procedure performed within a few days of the test if the ENT used cocaine as a local anesthetic), significant exposure to cocaine in your house/employment (such as individuals involved in large drug raids), or a laboratory error (specimen being mislabled/switched).

From a medical point of view, there is no other explanation. If as you stated, you have never used cocaine, then your only option at this point would be to consult an attorney who could address any possible violations of state/federal laws, errors in collection procedures or chain of custody.
Customer: replied 6 years ago.

I did not have an ENT or any other procedures nor any exposure to cocaine at home or work. I don't think there was error in the collection process nor do I have money for a lawyer. There HAS TO be some explanation for this result. This was a dip stick type test performed in the clinic. Something that does strike me to be odd is that I also take klonopin bid yet the test was neg for benzos. Not to question your expertise but I have found ALOT of information stating amoxicillin can cause false positives on several websites along with lidocaine & large amounts of caffeine (maybe not scientifically proven). Can you provide me with information or studies this information has been scientifically disproven? Also, does my PCP have any obligation or right to report these results to law enforcement or health boards since I am a Licensed nurse?

If this was only done with a dipstick, this type of testing would be considered "screening". To be defensible from a legal/scientific basis, a drug test really should be confirmed with GC/MS.

While you can find sites that make such claims (amoxicillin, caffeine etc) on the web, you must understand that you can find nearly anything on the internet, including sites from those who believe that the earth if flat.

Here is the study that looked at the claims for amoxicillin

Here is an excellent review article on drug testing including a list of possible causes for false positive drug tests (by particular drug test), you will see that only coaine and coca tea (illegal to purchase in the USA since it contains cocaine) have been shown to cause false positives.

Even if you can find some source that makes such a claim, you really are going to have to "accept" this dismissal OR pursue legal action to see if you can overturn the decision.

I am not trying to be difficult, I am just trying to give you the scientific evidence. An attorney could attack the accuracy of the test, problems in the manufacturing process, testing procedure and the failure to confirm the test with GC/MS.
Customer: replied 6 years ago.
My concern is really not being dismissed from this practice because as a medical professional myself and compassionate nurse, I feel if a patient does have a positive drug screen for any illegal substance that would indicate addiction disease the patient should be offered help not dismissal. I am in the process of finding another PCP. My concern is this urine screen result being on my permanent medical record, my professional reputation, or being reported to the board of health affecting my nursing license since I do not have thousands of dollars for lawyers or according to your expertise (which I greatly appreciate) any way of disproving the result on my own. Do you know if the practice can release this result without my consent? and why would the test be negative for benzo when I take klonopin bid?
I can understand. For some reason when I first read your question, I was thinking that this was an employment issue (drug testing for employment), in which case, pursing legal action would be important.

Your best option at this point would be to have a hair test performed. Your new PCP could order this at a number of national laboratories such as Quest Diagnostics or LabCorp who offer this type of testing. Both of these labs offer collection sites throughout the country.

I am curious why the doctor did the drug test in the first place?
Customer: replied 6 years ago.
Due to the epidemic of rx narcotics being sold on the streets, like many practices now, she does routine drug screens on all patients she prescribes any controlled substances to, in my case klonopin for anxiety and percocet for arthritis(I cant take Nsaids). Which to me would give her cause to question the results or at the very least speak to me about it. Really who would go to an appointment knowing a urine drug screen will be performed with cocaine in their system? I will request the hair follicle test with a new PCP if thats the only way to disprove the result. Do you have an answer as to why the klonopin didn't test positive? I take it every morning & afternoon (including the morning of my appt)??
The immunoassay tests for benzodiazepines are less than 100% effective at identifying all of the benzodiazepines. Klonopin is one of the benzodiazpines that most immunoassays are less effective at identifying. This is NOT uncommon, and in many situations perfectly normal.

Family Physician, Board Certified MRO
Category: Drug Testing
Satisfied Customers: 12816
Experience: Medical Review Officer - Physician Trained and certified in drug test interpretation
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