Why is a patient taking amphetamine salt combo (amphetamine) 15mg in the morning and 15mg XL (extended release) in the evening, along with Wellbutrin XL (bupropion), consistently testing positive for amphetamine and methamphetamine on drug tests?

Bupropion Can Cause False Positive Amphetamine Results on Drug Tests

Bupropion (Wellbutrin XL) is the most likely cause of your patient's false positive urine drug screens for amphetamines and methamphetamines. 1

Why This Is Happening

• Bupropion is well-documented as the most frequent cause of false positive amphetamine results on urine drug screens, with studies showing it accounts for 41% of false positive amphetamine results 1
• Standard immunoassay drug tests (the type commonly used in clinical settings) are susceptible to cross-reactions that can produce false-positive results, limiting their specificity 2
• The patient's prescribed amphetamine salt combo would naturally cause positive amphetamine results, but the methamphetamine positives are likely due to the bupropion cross-reactivity 1

Confirming the False Positive

• Confirmatory testing using gas chromatography-mass spectrometry (GC-MS) can definitively distinguish between true amphetamine/methamphetamine use and false positives caused by medications 2
• When interpreting drug test results, clinicians must know the patient's complete medication history, including all prescribed medications like bupropion 3
• False positives for amphetamines can occur with several medications, but bupropion has the highest association rate compared to other antidepressants 1

Managing This Situation

1. Document in the patient's chart that they are prescribed both amphetamine salts and bupropion, which can cause false positive drug screens 3, 1
2. Request confirmatory testing using GC-MS when drug test results are unexpected or will impact clinical decisions 4
3. Provide the patient with documentation explaining their medication regimen and the known cross-reactivity of bupropion with amphetamine screens 4

Important Considerations

• Qualitative drug screens (immunoassays) are designed as screening tests and are known to have limitations in specificity 2
• The patient's prescribed amphetamine salt combo would naturally cause positive amphetamine results, but the bupropion is likely contributing to the methamphetamine positives 1
• Many providers have inadequate training in interpreting drug test results, and incorrect interpretation can have serious consequences for patients 4

Pitfalls to Avoid

• Don't assume the patient is misusing substances based solely on immunoassay results without confirmatory testing 4
• Avoid making clinical decisions based on unexpected drug test results without consulting laboratory personnel or toxicologists 4
• Don't overlook that standard drug testing panels have significant limitations and may not accurately distinguish between prescribed medications and illicit substances 2

Additional Medications That Can Cause False Positive Amphetamine Results

• Other medications that can cause false positive amphetamine results include:
  • Atomoxetine 5
  • Aripiprazole 6
  • Metoprolol 7
  • Solriamfetol 8
  • Pseudoephedrine (in over-the-counter cold medications) 2

Understanding these medication interactions with drug testing is essential for proper patient care and avoiding incorrect assumptions about substance use.