Medications That Cause False-Positive Drug Tests
Bupropion, pseudoephedrine, dextromethorphan, poppy seeds, fluoroquinolone antibiotics, metoprolol, phenylephrine, and trazodone are the most commonly documented causes of false-positive drug screens, with confirmatory testing by gas chromatography-mass spectrometry (GC-MS) required before making any clinical decisions based on positive immunoassay results. 1, 2, 3
Amphetamine/Methamphetamine False Positives
The following medications and substances cause false-positive amphetamine or methamphetamine results:
- Bupropion - The FDA label explicitly states that bupropion can cause false-positive urine test results for amphetamines 3
- Pseudoephedrine (found in over-the-counter cold medications) - This is the most commonly cited cause of false-positive amphetamine screening results 1, 2
- Metoprolol (beta-blocker) - Can cause false positives for both amphetamines and MDMA at therapeutic concentrations, with metoprolol showing positive results at 200 μg/mL for amphetamines and 150 μg/mL for MDMA 4
- Phenylephrine - Has documented cross-reactivity with methamphetamine immunoassays due to similar chemical structures 5
- Ephedrine - Can cross-react with amphetamine screens, particularly when present in high concentrations 6, 7
- Phentermine - Shares identical base peak ions with methamphetamine in mass spectrometry analysis 7
Opiate False Positives
- Poppy seeds - Cause false-positive results for both morphine and codeine on screening AND confirmatory tests (GC-MS), making this a unique interferent 1
- Fluoroquinolone antibiotics - Can cross-react with opiate immunoassay screens 2
- Dextromethorphan (cough suppressant) - Documented to cause false-positive opiate results 1
MDMA (Ecstasy) False Positives
- Metoprolol - Cross-reacts with MDMA immunoassays at concentrations as low as 150 μg/mL 4
THC (Marijuana) False Positives
- No evidence exists linking trazodone to false-positive THC results, despite common clinical belief 8
Critical Clinical Actions
When encountering a positive drug screen:
- Obtain complete medication history including all prescription medications, over-the-counter drugs, and supplements before interpreting any positive result 1, 2
- Request confirmatory testing using GC-MS before making any consequential clinical decisions, as immunoassay screening tests are presumptive only and have known limitations in specificity 1, 2
- Never make clinical decisions based solely on immunoassay results - Standard immunoassay drug tests are susceptible to cross-reactions that limit their specificity 1, 8
- Consult with laboratory personnel or toxicologists when results are unexpected or will impact patient management 2
Important Caveats
- Pain medications given during labor and delivery can cause false positives, so the American College of Obstetricians and Gynecologists recommends testing women immediately on admission before administering any medications 1
- Standard drug panels often don't include commonly abused substances like fentanyl, carfentanil, buprenorphine, MDMA, ketamine, or gamma-hydroxybutyrate 1
- Methylphenidate is NOT detected on routine amphetamine panels, so positive amphetamine results cannot be explained by methylphenidate use 2
- Amphetamine/dextroamphetamine for ADHD will produce positive amphetamine tests, representing appropriate medication use rather than abuse 2
- Many providers have inadequate training in interpreting drug test results, and incorrect interpretation can have severe consequences including loss of child custody or legal implications 2