Several prescription medications that have nothing to do with benzodiazepines can trigger a positive result on a standard urine drug screen. The most well-documented culprits are the antidepressant sertraline (Zoloft), the HIV medication efavirenz (Sustiva), and the anti-inflammatory drug oxaprozin (Daypro). These false positives happen because the initial screening test works by recognizing molecular shapes rather than identifying exact chemicals, so anything with a similar enough structure can fool it. The story gets more complicated when you factor in designer benzodiazepines, lab processing quirks, and the gap between a screening test and a confirmatory one.
Why Screening Tests Get Tricked in the First Place
Most workplace, clinical, and criminal-justice urine drug tests start with an immunoassay. This is a fast, inexpensive test that uses antibodies designed to latch onto benzodiazepine-shaped molecules. The antibodies are not perfectly selective. They are built to cast a wide net so they catch as many true positives as possible, but that wide net also snags molecules that merely resemble benzodiazepines. The test reports a result above or below a cutoff concentration, and anything above that cutoff is called “presumptive positive.”
Different immunoassay platforms use different antibodies, which means the list of substances that cause false positives varies depending on which brand of test kit the lab uses. The three most common commercial platforms are EMIT, CEDIA, and FPIA, and each has its own quirks. A substance that reliably fools one platform might not register on another. This inconsistency is one reason false positives can be so confusing for the person being tested: the same medication might cause a problem at one testing facility and not at another.
Even among actual benzodiazepines, the immunoassay does not treat every drug equally. Some benzodiazepines are dramatically overestimated by certain assays. In one study of the EMIT platform, pinazepam produced cross-reactivity readings nearly seven times the expected concentration, while delorazepam showed roughly double the expected concentration.1Journal of Pharmaceutical and Biomedical Analysis. Cross-reactivities and structure–reactivity relationships of six benzodiazepines to EMIT® immunoassay If the test struggles to measure known benzodiazepines accurately, it is easy to see how structurally similar non-benzodiazepine molecules can slip through.
Sertraline and Antidepressant False Positives
Sertraline, sold under the brand name Zoloft, is the best-studied cause of false-positive benzodiazepine results on urine immunoassays. A retrospective chart analysis of over 500 urine drug screens found 160 confirmed false positives. After excluding patients who were also prescribed actual benzodiazepines, 26 of the remaining 98 false positives were linked to sertraline prescriptions.2PubMed Central. False-Positive Urine Screening for Benzodiazepines: An Association with Sertraline?: A Two-year Retrospective Chart Analysis That is a notable proportion, especially for a medication prescribed to millions of people for depression and anxiety.
The cross-reactivity is not limited to sertraline itself. Its metabolites, the breakdown products the body creates as it processes the drug, also interact with the immunoassay antibodies. Early versions of the CEDIA benzodiazepine assay were known to cross-react with both sertraline and its metabolites, though the manufacturer later released an improved version designed to reduce this interference.3Journal of Analytical Toxicology. Improved CEDIA® Benzodiazepine Assay Eliminates Sertraline Crossreactivity Whether the version of the assay used at your testing facility is old or new matters. Labs that have not upgraded to the newer formulation may still produce sertraline-related false positives.
If you take sertraline and are facing a drug test, this is worth knowing ahead of time. Disclosing your prescription to the medical review officer before the test, or requesting confirmatory testing if the screen comes back positive, can save a lot of unnecessary trouble. The confirmatory test, which uses mass spectrometry to identify the exact molecules present, will not mistake sertraline for a benzodiazepine.
Efavirenz and HIV Treatment
Efavirenz, a non-nucleoside reverse transcriptase inhibitor used in HIV treatment, is perhaps the most dramatic source of false-positive benzodiazepine screens. In a study comparing 50 patients on efavirenz to 50 patients not taking the drug, 49 of the 50 efavirenz patients tested positive for benzodiazepines on at least one drug screen. Only one patient in the control group tested positive.4PubMed. Efavirenz treatment and false-positive results in benzodiazepine screening tests The false-positive rate was essentially universal among people taking the medication.
The culprit is a metabolite called 8-hydroxy-efavirenz. As the body breaks down efavirenz, it produces this compound, which apparently mimics the benzodiazepine structure closely enough to set off the immunoassay. The clinical implications are significant. People living with HIV may already face stigma in healthcare settings, and a positive benzodiazepine screen on top of that can lead to inappropriate assumptions about substance use. Clinicians who order drug screens for patients on efavirenz need to be aware of this interaction, and patients should feel empowered to mention it if they are asked about a positive result.
Efavirenz has become less commonly prescribed in recent years as newer HIV medications with fewer side effects have taken its place. But it remains part of some treatment regimens, particularly in resource-limited settings, so the false-positive issue is far from obsolete.
Oxaprozin, an Anti-Inflammatory Drug
Oxaprozin, marketed as Daypro, is a nonsteroidal anti-inflammatory drug (NSAID) prescribed for arthritis and other painful conditions. Unlike more commonly used NSAIDs such as ibuprofen or naproxen, oxaprozin has a well-documented tendency to trigger false-positive benzodiazepine results. In a controlled study involving 12 subjects, every single urine sample tested positive for benzodiazepines on EMIT and CEDIA assays, and all but one tested positive on the FPIA assay.5PubMed. Oxaprozin cross-reactivity in three commercial immunoassays for benzodiazepines in urine
What makes oxaprozin stand out is the sheer magnitude of the cross-reactivity. The concentrations detected in some assays ranged from 5,000 to 10,000 nanograms per milliliter, well above the typical 200 nanogram-per-milliliter cutoff used for benzodiazepines. This is not a borderline result that might slip through on a bad day; it is a strong, unambiguous positive on the screening test, all from a standard dose of an arthritis medication.
Other NSAIDs do not share this problem. If you are taking ibuprofen, naproxen, or aspirin, you do not need to worry about a false-positive benzodiazepine screen. The cross-reactivity is specific to oxaprozin and its metabolites. That said, oxaprozin is not prescribed as frequently as it once was, so this issue affects a smaller population than the sertraline problem.
The Big Three and Whether Others Belong on the List
Sertraline, efavirenz, and oxaprozin are consistently identified as the primary medications causing false-positive benzodiazepine results across the medical literature. You may come across longer lists online that include other medications. Some of these claims are based on isolated case reports or theoretical cross-reactivity rather than controlled studies. The evidence is strongest for the three substances above, and reference compilations of interfering medications consistently point to the same trio.6Journal of Analytical Toxicology. False-Positive Interferences of Common Urine Drug Screen Immunoassays: A Review
What about other antidepressants, antipsychotics, or common over-the-counter drugs? Most do not cause benzodiazepine false positives specifically, though many medications can interfere with other drug screens (amphetamine screens, for instance, are notorious for false positives from a much longer list of medications). If you come across a claim that a specific medication causes a false-positive benzodiazepine result and it is not one of the three described here, it is worth checking whether the claim is backed by a controlled study or just an anecdotal report.
What About Herbal Supplements and Food?
This is one area where the news is actually reassuring. A study that tested a range of common herbal supplements found that none of them produced false-positive results on urine drug screens analyzed by enzyme immunoassay.7PubMed. Common herbal supplements did not produce false-positive results on urine drug screens analyzed by enzyme immunoassay While certain herbal products and foods are known to interfere with other drug categories on screening tests, the benzodiazepine immunoassay appears to be relatively resistant to interference from dietary and botanical sources.
You may have seen claims that valerian root, kava, or chamomile could trigger a positive benzodiazepine screen because these herbs act on some of the same brain receptors that benzodiazepines target. Acting on the same receptor in the brain is not the same as looking like a benzodiazepine molecule to an antibody in a test tube. The immunoassay responds to chemical structure, not pharmacological activity. So even supplements marketed for their calming or sedative properties do not cross-react with benzodiazepine screening panels.
Designer Benzodiazepines and the Confirmation Gap
A growing problem in drug testing involves novel psychoactive substances, sometimes called designer benzodiazepines. These are compounds with benzodiazepine-like structures that are not approved by the FDA and are typically purchased online or found in illicit drug supplies. Names like flualprazolam, flubromazolam, clonazolam, and etizolam have become increasingly common in toxicology reports.
These substances do trigger positive benzodiazepine immunoassay screens, which makes sense since they are structurally close to prescription benzodiazepines. The problem comes during the confirmation step. When a screening test is positive, labs typically run a confirmatory test using mass spectrometry to identify the specific drug present. But most confirmatory panels are designed to look for a set list of FDA-approved benzodiazepines and their known metabolites. If the substance in the urine is flubromazolam or etizolam, it will not match anything on that list. The result gets reported as a “false positive” from the screening test, even though a benzodiazepine-class substance was genuinely present.8Journal of Analytical Toxicology. Urine Drug Screening in the Era of Designer Benzodiazepines: Comparison of Three Immunoassay Platforms, LC–QTOF-MS and LC–MS-MS
One study examined 35 urine specimens that screened positive for benzodiazepines and found that 30 of them contained at least one non-FDA-approved benzodiazepine. Multiple designer compounds were detected simultaneously in over a third of those specimens. Yet when the same samples were run through a standard confirmatory panel, many would have been dismissed as false positives because the panel did not include those specific drugs.9Journal of Addiction Medicine. Evidence of Designer Benzodiazepine Use in Routine Healthcare Urine Drug Specimens This creates a dangerous blind spot: clinicians may assume a patient is not using benzodiazepines when they actually are, just not the ones the lab is set up to detect.
The solution is expanded confirmatory panels that include designer benzodiazepines, and some labs have begun developing these. Researchers have demonstrated methods using high-resolution mass spectrometry that can screen for 28 or more novel benzodiazepines in urine.10Clinical Mass Spectrometry. Urine analysis of 28 designer benzodiazepines by liquid chromatography–high-resolution mass spectrometry But widespread adoption takes time, and many clinical and forensic labs still use panels that miss these compounds entirely.
Why Confirmatory Testing Is Non-Negotiable
Every positive immunoassay screen for benzodiazepines should be confirmed with a second, more specific test before anyone draws conclusions. The gold standard is gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-tandem mass spectrometry (LC-MS/MS). These methods identify the actual molecules present in the sample rather than relying on antibody binding, which means they can distinguish sertraline from diazepam, or efavirenz metabolites from alprazolam.
In workplaces and legal settings governed by federal guidelines, confirmatory testing is required before a positive result is reported. But in many clinical settings, the screening result alone may be acted upon without confirmation. A doctor might see a positive benzodiazepine screen and make treatment decisions, refuse to prescribe certain medications, or note potential substance misuse in a medical chart based solely on that preliminary result. If you know you are taking a medication that can interfere, asking whether confirmatory testing was performed is a reasonable and important step.
How the Lab Processes Your Sample Matters Too
Even when the right drugs are present in urine, the lab’s preparation methods can affect whether they show up. Many benzodiazepines are extensively metabolized in the body, and their breakdown products are excreted in urine primarily as glucuronide conjugates. These are molecules that the body has chemically tagged for excretion. In this conjugated form, they are harder for both immunoassays and confirmatory tests to detect.
To address this, labs use an enzyme called beta-glucuronidase to break apart those conjugates before running the test. If this hydrolysis step is incomplete, the test may underestimate or miss benzodiazepines that are genuinely present, producing a false negative. The time and temperature of incubation matter. Research has shown that a 15-minute incubation may be insufficient to fully break glucuronide bonds, while 30 minutes at 55 degrees Celsius appears to complete the process.11LVHN Scholarly Works. Rapid Hydrolysis of Benzodiazepines in Urine The efficiency of hydrolysis can also differ between individual benzodiazepine metabolites, with some glucuronide forms being more stubborn than others.12Forensic Science International. Validation of benzodiazepine β-glucuronide primary reference materials for hydrolysis and quality assurance controls
This is not something you as the person being tested can control, but it is worth understanding if your results seem inconsistent. A negative result does not always mean no benzodiazepine was present; it could mean the lab’s processing did not fully liberate the drug from its conjugated form. The development of faster, more effective hydrolysis enzymes is an active area of lab science for this reason.13Journal of Analytical Toxicology. Rapid Enzymatic Hydrolysis Using a Novel Recombinant β-Glucuronidase in Benzodiazepine Urinalysis
Detection Windows and Why Timing Matters
Even setting aside false positives and lab processing, the question of what “shows up” on a benzodiazepine urine test depends heavily on when the test happens relative to when the drug was taken. Different benzodiazepines have vastly different detection windows. Short-acting benzodiazepines like triazolam or midazolam may be detectable for only a day or two. Long-acting ones like diazepam (Valium), which produces active metabolites that linger in the body for weeks, can test positive for a month or more after a single dose.
Lorazepam offers a useful example of intermediate detection. After a single oral dose, urine concentrations peak at around 24 hours and remain detectable for roughly six days, with concentrations dropping into the low single-digit nanograms-per-milliliter range toward the end of that window.14Elsevier. Windows of detection of lorazepam in urine, oral fluid and hair, with a special focus on drug-facilitated crimes How quickly the drug clears depends on your metabolism, kidney function, body composition, hydration status, and the dose taken. Chronic users accumulate the drug and its metabolites, extending the detection window considerably compared to someone who took a single dose.
This variability means a negative test does not prove you never took a benzodiazepine, and a positive test does not tell you exactly when the drug was used. It tells you only that the substance or its metabolites were present in your urine above the assay’s cutoff at the moment the sample was collected.
Non-Benzodiazepine Sleep Aids
A common question is whether “Z-drugs” like zolpidem (Ambien), zaleplon (Sonata), or eszopiclone (Lunesta) will trigger a positive benzodiazepine screen. These medications work on the same type of brain receptor as benzodiazepines, and they are often grouped with benzodiazepines in casual conversation, but their chemical structures are different. In general, the Z-drugs do not cross-react with standard benzodiazepine immunoassays. Their molecular shapes are distinct enough that the screening antibodies do not bind to them. So if you are taking Ambien for insomnia and nothing else, you should not expect a positive benzodiazepine screen.
The same logic applies to other medications that are sometimes called “benzo-like” because of their sedative effects. Gabapentin, pregabalin, muscle relaxants, and antihistamines may all produce sedation, but sedation is a pharmacological effect, not a chemical structure. The urine test is looking for structure, not effect. Unless a medication happens to share the fused benzene-and-diazepine ring system that defines the benzodiazepine class (or something close enough to confuse the antibody), it will not register on the screen.
What to Do If You Get a Surprising Positive
If your urine drug screen comes back positive for benzodiazepines and you do not believe you have taken any, start by reviewing your current medication list against the known cross-reactants: sertraline, efavirenz, and oxaprozin. If you are taking any of these, that is your likely explanation. Request confirmatory testing if it has not already been performed, and make sure the medical review officer or ordering clinician knows about your medications.
If none of those medications apply, consider whether you may have been unknowingly exposed to a benzodiazepine or a designer benzodiazepine through illicit drug use or contaminated substances. Designer benzodiazepines have been found in counterfeit pills and in heroin and fentanyl supplies, and a person may not know they have been exposed. In that case, asking the lab whether their confirmatory panel includes designer benzodiazepines may be worthwhile, though many labs do not yet offer this.
Keep in mind that immunoassay false positives, while inconvenient and sometimes alarming, are a known and well-documented phenomenon. The test was designed to err on the side of catching true positives, which means some false positives are built into the system. The confirmation step exists precisely because the screening step is imperfect. If you are in a situation where the stakes of a positive result are high, such as employment, custody proceedings, or pain management agreements, understanding this two-step process and advocating for the confirmatory test is the single most important thing you can do.