As unbelievable as it seems, poppy seeds do sometimes cause false positives on tests for heroin. The New York Times explains:
Eating a couple of bagels heavily coated with poppy seeds can result in morphine in a person's system for hours, leading a routine drug test to come back positive. A subsequent test can rule out heroin, though not other opiates, by looking for a specific metabolite, 6-acetylmorphine.
For years, the federal government set the test threshold for opiates in urine at 300 ng/ml. But false positives abounded in poppy seed bagel lovers. A single teaspoon of poppy seeds, for example, produce opiate concentrations of 1,200 ng/ml. And so eventually, the National Institute on Drug Abuse raised the cut-off way up, to 2,000 ng/ml. The army took an even more cautious approach, setting the cut off at 3,000 ng/ml.
After years of discouraging people from eating poppy seed pastries prior to job interviews (and perhaps missing some heroin users in screening tests), researchers from King's College London think they've finally found a fix. They analyzed street heroin and compared its components to poppy seeds until they found a unique molecular ingredient in heroin that poppy seeds lack: a glucuronide metabolite called ATM4G. The metabolite, they say, dependably turns up in users' urine but is not present in seed-lovers' systems.
The researchers haven't developed a commercial test yet, but one will likely be coming soon if their results continue to stand up to further testing. It's hard to imagine that many heroin users have actually used this as an excuse, but—if that's true of you—as Gizmodo writes, "now would probably be a good time to get off the horse if you're looking to keep your job."
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