"A number of different types of psychiatric medications can cause false positives on urine tests. Librium (chlordiazepoxide), an anti-anxiety medication also used to control agitation during alcohol withdrawal, can cause false positive pregnancy results in urine pregnancy tests, Medline Plus states, but blood tests will not show false positive results. Phenothiazines and phenothiazine derivatives are antipsychotic medications used to treat psychiatric disorders that can also give false positive results on urine pregnancy tests. Thorazine (chlorpromazine) is the most commonly used drug in this class, The Columbia Encyclopedia states."