Which antipsychotic may cause a false positive methadone on urine drug screens?

• A. Quetiapine
• B. Ziprasidone
• C. Olanzapine
• D. Risperidone

Answer: (A)

The main idea is cross-reactivity in urine drug screens. Immunoassay tests for methadone can be fooled by certain non-methadone medications because the antibodies used in the screen may recognize similar chemical structures. Quetiapine, and some of its metabolites, have been reported to trigger a positive methadone result on these immunoassays even when methadone isn’t present. That’s why it can appear as a false positive.

In practice, a positive methadone screen should be followed by a confirmatory test such as GC-MS or LC-MS/MS to determine the true substance.

The other antipsychotics listed are not typically associated with this cross-reactivity, so they’re less likely to cause a false-positive methadone result on standard screening.