Drug testing for benzodiazepines is common in various settings, including employment screenings and medical evaluations. While these tests aim to accurately detect substances, certain common medications can sometimes lead to unexpected “false positive” results. This occurs even when an individual has not consumed benzodiazepines. Understanding this phenomenon is helpful for anyone undergoing such testing.
Understanding Drug Tests for Benzodiazepines
Drug tests for benzodiazepines in urine use a two-stage process. The initial screening is an immunoassay, which uses antibodies to detect benzodiazepines or their metabolites. This screen is not highly specific and can cross-react with other substances that have similar chemical structures, leading to a presumptive positive result. If the initial screen is positive, a confirmatory test, such as Gas Chromatography-Mass Spectrometry (GC-MS) or Liquid Chromatography-Mass Spectrometry (LC-MS), is performed. These confirmatory tests are highly accurate and can differentiate between benzodiazepines and other compounds, providing a definitive result.
Common Medications Causing False Positives
Several common over-the-counter and prescription medications have been reported to cause false positive results for benzodiazepines on initial immunoassay screens. Non-steroidal anti-inflammatory drugs (NSAIDs) like oxaprozin (Daypro) are among these, with some reports indicating a potential for false positives. While ibuprofen (Advil, Motrin) and naproxen (Aleve) are less commonly associated with false positives for benzodiazepines, they have been linked to false positives for other drug classes. Antidepressants, particularly selective serotonin reuptake inhibitors (SSRIs) such as sertraline (Zoloft) and fluoxetine (Prozac), have also been confirmed to produce false positive benzodiazepine results on urine drug screens. False positives from sertraline may persist for several days after discontinuing the medication. Antihistamines, including diphenhydramine (Benadryl) and doxylamine (found in Unisom and other sleep aids), are frequent culprits due to their chemical similarities. Other medications that can lead to false positives include certain antipsychotics like quetiapine (Seroquel), although this is less commonly cited for benzodiazepine cross-reactivity specifically. Antimalarial drugs, such as quinine, have also been listed as potential causes. Certain antibiotics, while more often associated with false positives for opiates, may also contribute to false benzodiazepine results in some cases. Additionally, some herbal supplements like Valerian root, and various cold and flu medications containing antihistamines, can trigger false positives.
The Science Behind False Positives
The primary reason certain medications cause false positives in initial drug screens for benzodiazepines lies in a phenomenon called “cross-reactivity.” Immunoassay tests rely on antibodies designed to bind to specific chemical structures of benzodiazepines or their metabolites. These antibodies are not always perfectly exclusive. Some non-benzodiazepine medications or their breakdown products possess chemical structures sufficiently similar to benzodiazepines, and when present in a urine sample, the antibodies may mistakenly bind to them. This mistaken binding triggers a positive signal, leading to a false indication of benzodiazepine presence, even though the actual drug is absent. Confirmatory tests, which use more precise methods, are necessary to distinguish between true positives and these cross-reactive results.
Steps to Take After a False Positive Result
If an individual receives a false positive result for benzodiazepines on a drug test, prompt action can clarify the situation by informing the testing facility or healthcare provider about all medications, including prescription drugs, over-the-counter medications, and any herbal supplements. Requesting a confirmatory test, such as GC-MS or LC-MS, is a key step. These advanced tests are highly specific and accurately differentiate between benzodiazepines and other substances. Maintaining accurate records of all medications taken, including dosages and dates, can help demonstrate medication use. If the false positive result has significant implications, such as for employment or legal proceedings, consulting with a healthcare professional or legal counsel may be advised.