Fioricet pcp false positive. . . . Will barbiturates (fioricet . . . . In 2007, a false-positive for the date rape drug GHB occurred . . It often exists in the system for 3 . . . . . . . . . Dept. Possible False Positive Sources: Amphetamine> What can give you a false positive drug test for meth? . . . I tested positive for Phenobarbital during a urine drug screen (GC MS). . . . AskDocWeb: The only drugs that have been reported to show up as a false positive for PCP are . I take Fioricet an... more