Many urine drug tests used to screen for drugs of abuse are immunoassays which can have false positive results. A urine test for amphetamines may be positive in the absence of an illegal drug.
Drugs that can cause a false-positive immunoassay for amphetamines:
(1) aripiprazole
(2) metoprolol or labetalol
(3) levomethamphetamine (L-methamphetamine), phenylephrine and other nonprescription sympathomimetic agents
(4) phenothiazines
(5) bupropion
(6) ofloxacin
(7) metformin
(8) trazodone
(9) dimethylamylamine (DMAA)
The list of interfering drugs is dependent on the method.
All positive screening tests need to be confirmed by a specific assay such as GC/MS.
Differential diagnosis: positive amphetamine test related to "precursor" drugs used in obesity that are metabolized to an amphetamine.
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