YES! This is true...at least when it comes to initial urine SCREENING tests.
     Certain substances can cause false positives on urine immunoassay-based screens...but the same sample will come back negative with a stricter laboratory-based test such as gas chromatography-mass spectrometry (GC-MS) or high-performance liquid chromatography (HPLC).
     SCREENING tests for opiates and amphetamines often result in false positives.
     For example, an OTC decongestant such as pseudoephedrine can look like an amphetamine on a screening test...so can bupropion, ranitidine, labetalol, or chlorpromazine.
     Please be aware that eating foods containing large amounts of poppy seeds can cause a false positive for opioids...so can rifampin and levofloxacin.
     Dextromethorphan can look like an opioid or PCP...and diphenhydramine, tramadol, and venlafaxine users can test positive for PCP.
      Screening tests are pretty good at picking up marijuana use...but taking an NSAID or PPI can result in a false positive.
      Labs usually run all positive screening results through more accurate and reliable lab-based confirmation tests. These tests CAN tell the difference between the real thing and legal drugs masquerading as illegal ones.
      SCREENING tests don’t always pick up all opioids in a patient’s system. Tell prescribers that typical urine screening for opiates only tests for morphine and codeine.      How long a person using drugs tests positive varies.
     Amphetamines or codeine use can usually be detected up to 2 days after a dose...cocaine and hydromorphone up to 2 to 4 days...and morphine for up to 2 to 3 days.
      Marijuana metabolites stick around quite a while. A single use can be picked up by a urine screen a week later...and multiple-day users can test positive up 4 to 6 weeks later.
     Detoxifying products (XXtra Clean, etc) aren’t proven to work...and labs can detect “doctored” urine.