What causes false positives for opiates in a drug test?

Answer:
Poppyseed bagels, since opiates come from the poppy plant. I saw it in an episode of Myth Busters, and it does indeed cause a false positive for opiates.
First answer by Tjeyw721. Last edit by Tjeyw721. Contributor trust: 12 [recommend contributor recommended]. Question popularity: 0 [recommend question].