What Can Cause A Gabapentin False-Positive On A Drug Test?
In our latest question and answer, the pharmacist discusses drug testing for gabapentin and what could cause a false-positive.
I tested positive for gabapentin but I haven't taken in 10 years or more. I am however taking Trileptal. Is it possible this drug along with others I am on (Celexa, Prilosec, Flonase, Celebrex, and albuterol) could have caused this reading?
Gabapentin (brand name Neurontin) is an antiepileptic drug but is most commonly used to treat neuropathic pain.
Gabapentin is not a controlled substance and isn't included on most standard urine drug screenings. Nevertheless, tests for it do exist.
Unfortunately, since it isn't commonly tested for, there is a notable lack of information regarding whether it can cause false-positive for other drugs or whether other drugs can cause a false-positive result for gabapentin.
Drug Testing For Gabapentin
Gabapentin is typically not tested for on most common urine drug screening tests for a number of reasons:
- It is not a controlled substance.
- It does not belong to a class of medication known for abuse, such as amphetamines, opioids, and benzodiazepines.
- It doesn't have a high likelihood of being abused.
Most common urine drug screenings are '5-panel' and are designed to detect the following:
- Amphetamines (e.g. amphetamine, methamphetamine, etc...)
- Opioids (e.g. codeine, morphine, heroin, hydrocodone, oxycodone, etc...)
- Phencyclidine (PCP)
Most studies suggest that gabapentin is highly unlikely to cause a 'false-positive' for any of the drugs being looked for on a standard 5-panel test due to its difference in structure and molecular composition.
Nevertheless, there are some studies that report that it may interfere with certain tests for amphetamines.
While gabapentin isn't commonly a drug that is tested for on drug screenings currently, this may change.
A number of studies are coming out reporting that it can be abused since it can cause euphoria at high doses and can increase the duration of a 'high' caused by opioids.
Since we may drug tests for gabapentin ordered more frequently, it would be prudent to have additional information on whether or not it can cause false-positive for other drugs or if other drugs can cause positive results for it.
Why Do False-Positives Happen?
Most urine drug tests are known as 'immunoassay' screenings since they utilize antibodies to bind to a particular drug substance in a sample. When an antibody binds to a compound (like gabapentin), it produces a reaction, which is then reported as a 'positive' result.
Immunoassay urine drug screenings have a well-known problem with 'cross-reactivity', which can cause erroneous results.
Sometimes, an antibody will bind to the wrong drug substance, and produce a reaction. While this would get recorded as a 'positive' result, it, in fact, is a 'false-positive'. Cross-reactivity most often occurs when drug compounds are similar in structure to the compound being tested for, but this isn't always the case.
What Can Cause A Gabapentin False-Positive?
There is currently no definitive information on other drugs causing a false-positive for gabapentin.
As mentioned above, most sources state that it would be unlikely for gabapentin to interfere with most drugs on the standard 5-panel drug test simply due to the differences in its molecular structure.
However, since most false-positives occur as a result of an antibody binding to a drug that has a similar structure, it makes sense that the risk of a false-positive gabapentin test is highest with other anti-epileptic drugs, or those similar to it.
Perhaps the most likely drug to cause a false-positive for gabapentin is Lyrica (pregabalin) since their molecular structures are very closely related.
In terms of the drugs that you are taking, you are on the antiepileptic drug, Trileptal (oxcarbazepine). There certainly is a chance that could cause a false-positive for gabapentin, but how likely this is isn't known.
What To Do If You Get A 'False-Positive' Result
Most studies discussing urine drug testing recommend that they should only be used as an initial screening since the incidence of false-positive results is high.
There are several other laboratory methods that can be used as a confirmatory test, such as gas chromatography-mass spectrometry. Drug tests using gas chromatography-mass spectrometry don't rely on antibodies and can accurately detect actual drug compounds in a given sample.
If you have the opportunity to request a confirmatory test to rule out your previous false-positive result, you should certainly do so!
- ^ Gabapentin for Adults with Neuropathic Pain: A Review of the Clinical Efficacy and Safety PubMed
- U.S. Pharmacist Urine Drug Screening: Minimizing False-Positives and False-Negatives to Optimize Patient Care.
- U.S. Pharmacist Abuse of Gabapentin is Associated with Opioid Addiction.
- American Association for Clinical Chemistry Pervasive Gabapentin Interference in the LC-MS/MS Analysis of Amphetamine.
- PubMed Immunoassays for drug screening in urine: Chances, challenges, and pitfalls.
- Mayo Clinic Proceedings Urine Drug Screening: Practical Guide for Clinicians.
- ClinicalKey (Subscription Required) Elsevier ClinicalKey: Lyrica Monograph.
- PubMed Commonly prescribed medications and potential false-positive urine drug screens.