Although confirmation methods should never produce false-positive results, the initial drug screens for opiates can sometimes be falsely positive. False-positive results for opiate after ingestion of poppy seeds can occur with urine drug screens. Poppy seeds contain the alkaloids morphine, and to a lesser extent, codeine. Ingestion of foods with poppy seeds usually causes only trace (very low) amounts of morphine in the urine (usually less than 500 ng/mL). Quantitating opiates with mass spectroscopy is often useful to help clinicians determine whether a positive opiate screen could have been due to poppy seeds (a low amount is seen) or prescription opiates (which would usually give higher concentrations). However there is no sure way to know, and no rule to apply in order to determine definitively whether a positive opiate result is due to poppy seeds or drug use.
Cough suppressants containing codeine and some quinolone drugs can also cause false-positive opiate results with some brands of immunoassays. Since many drugs of the opiate class can cross-react in drug screens, confirmation that an opiate is present and identification of the opiate that is present is important, especially for pain management.