Hydroxychloroquine, sold under the brand name Plaquenil among others, is a prescription antimalarial that is also used long term to manage lupus and rheumatoid arthritis. It is not a controlled substance, and it is not one of the drug classes that a standard employment drug test panel is built to detect. This article explains what a workplace drug screen actually looks for, what is and is not documented about hydroxychloroquine and related antimalarial compounds interfering with those screens, and what an employee on hydroxychloroquine should expect if they are asked to test.
What hydroxychloroquine is, and why it is not a panel target
Hydroxychloroquine is dispensed by prescription for malaria prevention and treatment and for long term control of systemic lupus erythematosus and rheumatoid arthritis. The current prescribing information, available through the National Library of Medicine's DailyMed database, does not list hydroxychloroquine as a federally controlled substance, and it carries none of the abuse potential warnings that accompany Drug Enforcement Administration scheduled drugs. You can review the full label here: Plaquenil (hydroxychloroquine sulfate) label, DailyMed.
Employment drug testing, whether it is a federally mandated DOT panel or a private employer's in house program, is not designed to flag every medication a person takes. It is designed to detect a specific, named list of drug classes. Under 49 CFR Part 40, the regulation that governs federal transportation workplace testing, laboratories test specimens for marijuana metabolites, cocaine metabolites, opioids, phencyclidine, and amphetamines (a class that includes methamphetamine and MDMA). The exact analytes and cutoff levels are published in the regulation itself: 49 CFR 40.85, drugs and metabolites laboratories test for. Hydroxychloroquine is not a cannabinoid, an opioid, a stimulant, phencyclidine, or a benzodiazepine. It does not belong to any class that a standard SAMHSA style five panel or an expanded ten or twelve panel immunoassay is built to detect, and non-DOT employer panels generally follow the same drug class structure.
Screening immunoassay versus confirmation testing
It helps to separate the two steps in a typical drug test. The first step, run on a cup, dip card, or oral fluid device, is an immunoassay. Antibodies in the test are designed to bind to a target drug or its metabolite, and a positive screen means the antibody detected something at or above a cutoff concentration. Immunoassays are fast and inexpensive, but they are a screening tool, not a legal determination. Antibodies can occasionally bind to a compound that is chemically similar to the intended target, which is how cross reactivity and false positive screens happen with some over the counter and prescription medications.
The second step, used whenever a screen comes back non-negative, is confirmation testing by gas chromatography mass spectrometry (GC/MS) or liquid chromatography tandem mass spectrometry (LC-MS/MS). These methods identify the exact molecule present rather than relying on antibody binding, and they are the standard that a laboratory and a medical review officer rely on before any result is reported as positive to an employer. A general overview of how screening and confirmation testing work together, including why a presumptive positive immunoassay result is not a final result, is available through the National Library of Medicine's StatPearls collection: Drug Testing, StatPearls, NIH Bookshelf.
What the evidence says about antimalarials and cross reactivity
Because hydroxychloroquine and chloroquine share a quinoline ring structure with quinine, people sometimes ask whether an antimalarial could trigger a false positive the way a handful of other quinoline family or related compounds occasionally have in older case literature. This is a fair question to ask, and the honest answer is that there is no published, peer reviewed evidence specifically documenting hydroxychloroquine causing a false positive on a standard SAMHSA panel immunoassay. The drug's own prescribing information, cited above, contains no laboratory test interference warning. StatPearls and similar clinical references on immunoassay cross reactivity discuss recognized interferents for specific drug classes such as opiates and amphetamines, but hydroxychloroquine does not appear as a documented interferent in that literature.
That distinction matters. "Not documented" is not the same as "100 percent ruled out", and no screening method can be called complete. If an employee taking hydroxychloroquine ever receives a non-negative screen, the correct response is confirmation testing and a review by the medical review officer, not a guess about the medication being the cause. The table below summarizes hydroxychloroquine and several related or commonly confused compounds.
| Drug | Class | Controlled substance | Documented panel cross reactivity |
|---|---|---|---|
| Hydroxychloroquine (Plaquenil) | 4-aminoquinoline antimalarial, DMARD | No | No published cross reactivity with standard SAMHSA panel immunoassays |
| Chloroquine | 4-aminoquinoline antimalarial | No | No published cross reactivity with standard SAMHSA panel immunoassays |
| Quinine | Cinchona alkaloid, antimalarial and leg cramp use | No | Chemically distinct from hydroxychloroquine; some older clinical literature on general immunoassay interferents exists for quinoline family compounds, not specific to hydroxychloroquine |
| Fluoroquinolone antibiotics (for example levofloxacin, ciprofloxacin) | Quinolone class antibiotics | No | Different drug class from hydroxychloroquine; reported opiate screen interference with some fluoroquinolones has been described and is addressed separately |
| Mefloquine | Quinoline methanol antimalarial | No | No published cross reactivity with standard SAMHSA panel immunoassays |
Because fluoroquinolone antibiotics are a different drug class with their own documented history, employees and employers should not assume hydroxychloroquine behaves the same way just because the names sound similar. Our related post on levofloxacin and opiate screen interference covers that class on its own.
What to do if a test comes back non-negative
Any presumptive positive result on a screening device should go through confirmation testing before anyone treats it as final. For DOT regulated testing, the process is spelled out in federal regulation: the laboratory confirms a non-negative screen, and a medical review officer, a licensed physician trained in substance abuse disorders and in reviewing test results, contacts the employee to ask about prescription medications and other legitimate explanations before a result is reported to the employer. That process is described in 49 CFR Part 40, Subpart G, the medical review officer and verification process. Non-DOT employers generally build their programs around the same MRO review step, following guidance published by the Substance Abuse and Mental Health Services Administration: SAMHSA, workplace substance use resources.
An employee taking hydroxychloroquine, or any prescription medication, should keep a copy of the prescription or a pharmacy printout on hand and be ready to share it with the MRO if asked. Nobody should try to interpret a non-negative screen on their own, and nobody should be given dosing advice or a diagnosis as part of that conversation. The MRO process exists specifically so that legitimate prescriptions, and legitimate questions about test accuracy, get resolved by a qualified medical professional rather than by guesswork.
What employers should keep in mind
For a program administrator, the practical takeaway is that hydroxychloroquine is not a reason to expect an abnormal screen, and it is not listed in panel documentation as an interferent. If a result does come back non-negative for an employee on hydroxychloroquine, the standard path, confirmation by GC/MS or LC-MS/MS followed by MRO review of prescription history, is the same path used for any other non-negative result. Employers that want a broader library of in house screening options for their own program can review the collection at American Screening Corporation drug test cups. For a wider look at medications that have documented interference histories, our general reference post on medications that can cause a false positive on drug tests is a useful companion read. Wholesale buyers can find volume pricing and account setup through the American Screening Corporation wholesale portal.
Frequently asked questions
Does hydroxychloroquine show up as a positive on a standard drug test panel?
No. Hydroxychloroquine is not a controlled substance and is not one of the drug classes, such as cannabinoids, opioids, cocaine metabolites, amphetamines, or phencyclidine, that a standard SAMHSA style panel immunoassay is built to detect.
Is there any published evidence that hydroxychloroquine causes a false positive?
No credible, published cross reactivity evidence links hydroxychloroquine to a false positive on standard panel immunoassays. The drug's prescribing information contains no laboratory test interference warning.
Is hydroxychloroquine the same as quinine for drug testing purposes?
No. They are chemically distinct compounds that both belong loosely to the broader quinoline family, but hydroxychloroquine is a synthetic 4-aminoquinoline, while quinine is a naturally occurring cinchona alkaloid. Neither has documented cross reactivity with standard panels, but they should not be treated as interchangeable.
What should an employee do if they take hydroxychloroquine and are asked to test?
Disclose current prescriptions honestly if asked, keep a pharmacy record available, and let the medical review officer process run its course on any non-negative result rather than assuming the medication is the cause.
What is the difference between a screening result and a confirmed result?
A screening immunoassay gives a presumptive result based on antibody binding at a cutoff level. A confirmed result comes from GC/MS or LC-MS/MS testing, which identifies the specific molecule present and is the standard used before a medical review officer reports any result as positive.
Does a positive drug test for an unrelated substance mean hydroxychloroquine caused it?
Not based on current evidence. Because no published research documents hydroxychloroquine interfering with standard panels, a non-negative result in a hydroxychloroquine patient should be worked up through normal confirmation and MRO review rather than attributed to the medication by default.
This article is general information about drug testing science and procedure, not medical or legal advice. Anyone with questions about a specific test result or a specific medication should talk to a medical review officer or their prescribing physician.