The other day, I caught a few minutes of the Seinfeld episode where Elaine Benes fails a drug test at work thanks to her fondness for the poppy seed muffins at Monk’s coffee shop. Can something as innocuous and innocent as a poppy seed pastry really make you look like a junkie?

Although opium is processed from the latex sap of the opium poppy (Papaver somniferum) and opiates are then extracted from that sap, all parts of the plant can contain or carry opium alkaloids, and the seeds often have a slight coating of the alkaloids from being in contact with the “seed pods.”

Because of this, opiates can be detected in urine sometimes up to 48 hours after ingestion of poppy seeds, which used to cause plenty of false positives on drug tests. You don’t “get high” from eating them, though, because the alkaloids break down at a relatively low temperatures. After baking, they’re still detectable, but too broken down to produce their well-known side-effects. It’s also worth noting that not all poppy seeds come from P. somniferum, the opium poppy.

Drug tests today have largely eliminated pastry-induced false positives.

The first part of this is using a two-step process where an immunoassay screening test identifies true negative samples and then, if necessary, a GC/MS (Gas Chromatography/Mass Spectrometry) confirmation testing — which identifies drug metabolites at the molecular level — is used on “non-negative” samples to rule out interfering substances.

The second fix is that, in 1998, the Department of Health and Human Services raised the screening and cutoff levels for the Opiate class from 300ng/mL to 2000 ng/mL, which helps to eliminate poppy seed interference with initial immunoassay screening.

It’s hard to make blanket statements about how many poppy seeds need to be ingested for a false positive — several factors that influences that, like body weight, vary from person to person — but a 1998 study [PDF] in Forensic Science International found that eating slices of cake with an average of 4.69 grams of poppy seeds on them was enough to cause four subjects to screen positive for up to 24 hours, with one person showing opiate levels of 302.1 ng/ml.

This is not an all-clear to go hogwild on poppyseeds, of course. Science blogger David Kroll wrote last year about a reader whose 17-year-old son died from drinking too much poppy seed tea:

"…Related specifically to Tom's comment, he has courageously posted a redacted version of the medical examiner's report from 13 Sept 2003. Therein, the toxicology analysis of tissues, blood, and the tea his son ingested are detailed. On the third page, the content of the tea was quantified as having a "high level of morphine," 259 micrograms/mL [equivalent to 259,000 nanograms, the measurement used in drug tests mentioned above]. Calculating a lethal dose for morphine is difficult because previous use of morphine can causes significant tolerance, or resistance, to both the therapeutic and lethal effects of the drug. For example, a dose of 100-150 mg may be lethal to a person who has never taken morphine orally, but it is not unusual for cancer patients with chronic pain to take as much as 4,000 mg/day.

Therefore, Tom's son could've received a lethal dose by drinking as little as a pint of the poppy tea he had prepared. [emphasis mine]

The medical examiner himself concluded the opinion section of the report by saying:

“Poppy seeds are the natural source of opioid analgesics. Although they contain extremely low levels of the drug, concentration of these compounds by brewing can result in potentially lethal levels.” [emphasis Kroll’s]