Will Lamictal (lamotrigine) show up on a urine drug screen?

Lamotrigine (Lamictal) and Urine Drug Screens

Lamotrigine (Lamictal) can cause false-positive results for phencyclidine (PCP) on standard urine drug screens, but it will not trigger positive results for other commonly tested substances. 1, 2

How Lamotrigine Appears on Drug Tests

• Standard drug panels: Lamotrigine is not specifically tested for in standard 10-panel urine drug screens 3
• False positives: Lamotrigine has been documented to cause false-positive results specifically for phencyclidine (PCP) on rapid urine toxicology screens 1, 2
• Confirmatory testing: When a false-positive PCP result occurs due to lamotrigine, confirmatory testing using gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-mass spectrometry (LC-MS) will correctly show negative results for PCP 1, 2

Case Evidence of False Positives

Multiple case reports have documented this cross-reactivity:

• A 62-year-old male and a 49-year-old female both tested positive for PCP on rapid urine screens while taking lamotrigine, but comprehensive confirmatory testing ruled out actual PCP use 1
• A 49-year-old male taking lamotrigine tested positive for PCP on a urine screen, but confirmatory blood testing was negative for PCP and positive for lamotrigine 2

Implications for Patients Taking Lamotrigine

1. Inform healthcare providers: Patients taking lamotrigine should inform any provider ordering a drug test about their medication
2. Documentation: Healthcare providers should document lamotrigine use when interpreting urine drug test results 3
3. Confirmatory testing: If a positive PCP result occurs in a patient taking lamotrigine, confirmatory testing should be performed before making clinical decisions 3, 4

Understanding Drug Testing Methodology

Standard urine drug testing is typically a two-step process:

1. Initial screening: Usually performed with immunoassays that can be subject to cross-reactivity 4
2. Confirmatory testing: Uses more specific methods like GC-MS or LC-MS to verify positive screening results 3, 4

Important Considerations for Clinicians

• Unexpected positive results should prompt a conversation with the patient rather than immediate punitive action 3
• Never dismiss patients from care based solely on urine drug test results without confirmatory testing 3
• Be aware that many medications can cause false positives on standard drug screens 3
• The American Academy of Pediatrics recommends specialized testing for confirmation of specific drug use 3

Avoiding Misinterpretation

• Always document all medications a patient is taking before interpreting drug test results
• Consider confirmatory testing when results don't match clinical presentation
• Remember that lamotrigine has a low abuse potential and doesn't cause sedation or impair psychomotor function 3, 5

Lamotrigine's cross-reactivity with PCP testing is an important clinical consideration that should be recognized by healthcare providers to prevent misdiagnosis and inappropriate management of patients taking this medication for legitimate medical purposes.