Diphenhydramine can cause a false-positive result for methadone in some rapid urine drug screening kits.
Basis for problem: diphenhydramine shares certain chemical features with methadone
Risk factors:
(1) rapid urine drug testing kit susceptible to interference with diphenhydramine
(2) sufficient diphenhydramine in the urine (reaction dose-dependent)
(3) testing method based on competitive binding
Problems can arise if:
(1) there is failure to confirm result with GC/MS or other definitive procedure
(2) failure to discuss possible explanations with the urine donor (MRO services)
(3) urine donor has a history of drug misuse
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Specialty: Emergency Medicine, Toxicology
