The pee-in-the-cup drug tests you may have to take at work can make mountains out of molehills and junkies out of breakfast lovers.

They can tell if there's chemical leftover in your body from breaking down opiates and drugs made from them, but not exactly where those metabolites came from. Some of the same chemicals will pop up on a screening whether you've been injecting heroin or doing something as innocent as eating poppy seed bagels.

Seinfeld's Elaine Benes and plenty of real-life folks have failed these tests because of breakfast-induced false positives. There have been a few workarounds to reduce testing errors like these, like raising the screening and cutoff levels, and running secondary tests of positive samples. But researchers at King's College in England have come up with a way to eliminate them entirely.

The team identified a molecule, dubbed ATM4G, in street heroin that's a by-product of the drug's manufacture, and isn't present in poppy seeds or prescription drugs and medicines that contain opiates. A chemical leftover unique to heroin, a metabolite called 6-MAM, has been found before, but its short half-life leaves it detectable in urine for only eight to 12 hours after heroin use.When researchers screened the urine of known heroin users, the metabolite clearly showed in around 75 percent of the samples, while 6-MAM was detected in only around 4 percent of the samples, and at low concentrations. Meanwhile, volunteers who were screened after eating yogurt loaded with poppy seeds showed no signs of ATM4G.

The researchers hope that their results could improve commercial drug tests. With ATM4G included in the markers of drug use that the tests screen for, testing companies would have an easier time finding heroin users without the extra cost and effort of following up on false positives.

As psychologist and neuroscience blogger Dana Smith points out, the test will need more work and refinement to increase the detection rate before its ready for use in the workplace, but its a promising start to a technique that could save bagel eaters a lot of trouble.