So it turns out some urban legends are true: You can test positive for drugs after eating a poppy seed bagel. “In fact, studies have shown that just a teaspoon of poppy seeds can cause your levels to be 1,200 nanograms per millimeter,” says WBAL-TV. At the hospital where Eden was giving birth, the limit was 300 nanograms. Something to keep in mind the day before or morning of your next job interview.