The best way to pass a drug swab test is to refrain from using drugs or alcohol for 24 to 72 hours prior to taking the test. In addition, it is important to avoid any foods containing poppy seeds, as these can lead to a false positive.
Although poppy seeds on a bagel, muffin or other food item are chemically harmless, consuming them can result in a failed drug test even if the person taking the test has not consumed any drugs. This is because poppy seeds come from the plant Papaver somniferum. Poppy seeds from this plant do not contain opiates, but the pods from which these seeds originate produce opium, which is the substance used to create drugs such as morphine and heroin. When poppy seeds are harvested for non-drug use, they become contaminated with opium from the seed pods. When the seeds are ingested, the opiates show up in the body's system, leading to a false positive.
Because of the increasing problem of false positives, the federal Substance Abuse and Mental Health Services Administration changed the positive reading threshold for opiate drug testing in 1998, raising it from 0.3 micrograms per milliliter to 2 micrograms per milliliter.