 Ingestion of codeine or food containing poppy seeds can cause false positives.A 1999 review estimated that relatively low doses of heroin (which metabolizes immediately into morphine) are detectable by standard urine tests for 1–1.5 days after use.A 2009 review determined that, when the analyte is morphine and the limit of detection is 1ng/ml, a 20mg intravenous (IV) dose of morphine is detectable for 12–24 hours.