Medications That Cause False-Positive Drug Test Results
Bupropion is the most common prescription medication causing false-positive amphetamine results, accounting for 41% of unconfirmed amphetamine screens in one study, and this is explicitly acknowledged in FDA labeling. 1, 2
Most Common False-Positive Culprits
Amphetamine/Methamphetamine False Positives
These are the most frequently reported false-positive results across all drug classes:
- Bupropion (antidepressant/smoking cessation aid) causes false-positive amphetamine screens due to lack of specificity in immunoassays, with 41% of unconfirmed positive amphetamine screens attributed to therapeutic bupropion use 2
- Pseudoephedrine (over-the-counter cold medications) triggers amphetamine false positives 3
- Promethazine (antihistamine/antiemetic) caused false-positive amphetamine results in 36% of patients using the EMIT II Plus Monoclonal assay, though newer assays show reduced interference 4
- Aripiprazole (antipsychotic) has been documented to cause false-positive amphetamine screens in pediatric cases 5
Other Antidepressants and Psychotropics
- Venlafaxine, sertraline, trazodone, and bupropion can all trigger false-positive amphetamine results 6
- Quetiapine, chlorpromazine, and thioridazine (antipsychotics) have been reported to cause false positives 6
Additional Medications Causing Various False Positives
- Dextromethorphan (cough suppressant) can cause false-positive results 7, 6
- Ranitidine (H2-blocker) has been associated with false positives 6
- Ibuprofen and naproxen (NSAIDs) can trigger false-positive results 6
- Quinolone antibiotics (ofloxacin, gatifloxacin) have been reported to cause false positives 6
- Diphenhydramine, brompheniramine, and doxylamine (antihistamines) can cause false-positive results 6
- Verapamil (calcium channel blocker) has been associated with false positives 6
Critical Clinical Considerations
Timing of Testing Matters
Women should be tested immediately on admission to labor and delivery settings before receiving any medications that could cause positive results, as pain medications given during delivery can cause false positives. 7
Understanding Test Limitations
- Preliminary screening immunoassays are more prone to false positives than confirmatory tests and should never be considered definitive 7, 8
- Standard drug panels often don't include commonly abused substances like fentanyl, carfentanil, buprenorphine, MDMA, ketamine, or gamma-hydroxybutyrate 7
- False-positive results can occur even after discontinuation of the medication 1
Confirmation Testing is Essential
Gas chromatography-mass spectrometry (GC-MS) is the gold standard confirmatory test that can definitively distinguish between true drug use and medication-induced false positives. 3, 1, 6
Common Pitfalls to Avoid
- Never act on preliminary screening results alone when the consequences are severe (child custody, legal implications, employment) 8
- Obtain complete medication histories including over-the-counter medications and supplements before interpreting results 3
- Be aware that different immunoassay manufacturers have vastly different interference profiles—what causes false positives in one assay may not in another 4
- Discuss unexpected positive results with your laboratory or toxicologist before taking clinical action 8
- Remember that poppy seeds can also cause false-positive opiate results 7
High-Stakes Contexts Require Extra Caution
The consequences of false-positive results can include loss of child custody, legal prosecution, loss of employment, or denial of pain management—making confirmation testing mandatory in these situations 8