In a patient taking buprenorphine, gabapentin, lamotrigine (Lamictal), prazosin, quetiapine (Seroquel), and sertraline, can any of these medications cause false‑positive results on a urine drug screen?

False-Positive Urine Drug Screen Results with This Medication Regimen

Among this patient's medications, quetiapine (Seroquel), sertraline, and lamotrigine (Lamictal) can all cause false-positive results on urine drug screens, while buprenorphine, gabapentin, and prazosin are not reported to cause false positives.

Specific Medications and Their False-Positive Patterns

Quetiapine (Seroquel)

• Causes false-positive results for tricyclic antidepressants (TCAs) on immunoassay screening 1, 2
• The cross-reactivity varies significantly between different immunoassay platforms 2
• Both therapeutic doses and overdose levels can trigger false positives 2
• This occurs because quetiapine has structural similarities to tricyclic antidepressants 2

Sertraline

• Causes false-positive results for benzodiazepines on immunoassay screening 1, 3
• In a two-year retrospective analysis, sertraline was associated with 26 out of 98 false-positive benzodiazepine screens that were later ruled out by confirmatory testing 3
• This represents an underreported but clinically significant source of false positives 3

Lamotrigine (Lamictal)

• Causes false-positive results for phencyclidine (PCP) according to FDA labeling 4
• The FDA explicitly warns: "Lamotrigine has been reported to interfere with the assay used in some rapid urine drug screens, which can result in false-positive readings, particularly for phencyclidine (PCP)" 4
• This is also confirmed in the research literature 5, 1

Medications NOT Causing False Positives

• Buprenorphine: No false-positive reports identified
• Gabapentin: No false-positive reports identified
• Prazosin: No false-positive reports identified

Critical Clinical Approach

When Interpreting Unexpected Positive Results

Always obtain confirmatory testing using gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-mass spectrometry (LC-MS) before making clinical decisions 6, 7. The guidelines emphasize that immunoassay screening tests are susceptible to false positives, and confirmatory testing is highly specific and will not confirm the presence of drugs that aren't actually present 7.

Before Ordering the Test

1. Review the patient's complete medication list with them 6
2. Explain that these three medications may cause false positives for TCAs, benzodiazepines, and PCP respectively
3. Document this discussion to prevent misinterpretation of results
4. Ask the patient if there might be unexpected results to allow candid disclosure 6

When Results Are Positive

1. Do not make clinical decisions based on immunoassay results alone 7
2. Discuss unexpected results with the laboratory or toxicologist before confronting the patient 6
3. Order confirmatory testing (GC-MS or LC-MS) for any unexpected positive that would affect management 6, 7
4. Never dismiss patients from care based on urine drug test results - this constitutes patient abandonment and eliminates opportunities for intervention 6

Common Pitfalls to Avoid

• Assuming immunoassay results are definitive: Immunoassays are designed for rapid screening but have known cross-reactivity issues 7, 1
• Not checking medication lists before interpreting results: This is the most preventable cause of misinterpretation 6, 1
• Failing to obtain confirmatory testing: Mass spectrometry will definitively rule out false positives 7, 3
• Making punitive decisions without confirmation: Guidelines explicitly warn against this approach due to patient safety concerns 6

Key Nuance

The likelihood and magnitude of false positives can vary between different immunoassay platforms and manufacturers 2. Some testing systems may show cross-reactivity while others do not, even when testing the same medication 2. This variability underscores why confirmatory testing is essential rather than optional when results don't match clinical expectations 7.