I believe the show Mythbusters did a segment on this. You might want to search for their results.

It could show for up to 48 hours from eating a single serving of poppy, but only poppy seeds from opium poppy plants. Now a days it's much more common to use non opium poppy plants, due to this issue. There is a test they can run to see if a drug test shows up and the person claims it to be poppy. Labs claim that hair analysis can distinguish between opiate abuse and poppy-seed ingestion. Additionally, the Feds are familiar with urine-adulteration tricks. Consequently, the Feds upped the ng/ml detection level beyond that of "normal" poppy-seed ingestion, but still within the range of abuse. Normal ingestion is considered to be like two poppy-seed muffins in a day, tops. Best bet is dont eat poppy if you get drug tests. If you are taking tests for leagle reasons they wont listen to any "poppy" stories, and breakfast is not worth your job. here is your mythbuster link http://www.mythbustersfanclub.com/mb2/content/view/15/27/

its not that relevant anymore in drug tests. i have eaten them the day before a test and had no problems. in fact it was poppyseed dressing, so i had eaten quite a bit.

While working at an urgent care center a patient came in for a required drug screening to get a job. Her test came back positive. She explained to them that she had eaten lemon poppy seed cake the day prior to taking the test. She wasn't aware that she should avoid eating it. The lab and the doctors at both facilities agreed that there was no way eating poppy seed cake could create a positive drug test, they informed the employer, also. She was denied the job. She returned to our facility a couple of weeks later with poppy seed cake. She requested that a urine sample be taken prior to eating the cake. She then sat there and consumed the same amount of poppy seed cake that she had the day prior to the original drug screen test. Approximately two hours after eating the poppy seed cake she requested that another urine sample be taken "post poppy seed consumption". When the test results came back the first urine sample, before eating the poppy seed cake, came back negative for opiates. However the second urine specimen, taken after eating the poppy seed cake, came back positive for opiates. She demanded that a letter of apology be written to her by both the doctors, at the urgent care facility and the lab that had done the drug test. She also request a copy be sent to the company who denied her employment because of the results. She stated that it was too late for her to get the job but she wanted her name and reputation to be cleared. So all the answers I have read that state that poppy seeds in food do not create positive drug test doesn't ring true for me as I have seen the results of that belief.

they dont it is a myth you would need to eat a cup full or more .

- Dr. Peter Walsh, Throughout the drug tests i have given of my 20 years in medical standards, there have been positive and negavtive drug test results of Poppy Seeds. But i shal say from only a single poppy seed muffin the tests taken have resulted as negatives along with 2 muffins.

I agree with the Doctor. It takes a LOT of poppy seeds to show up in a urine analysis. I do know the poppy seeds in California do show up positive in a drug test with just ONE muffin. I had a friend that was on Probation, and he didn't do drugs. But when had to be drug screened the day after eating the poppy seed muffin, it did show up positive, and he had to go to jail. So it depends where the seeds came from. Some won't show them at all in a drug test, some do. It's just how it is. And if you live in California, and eat a poppy seed muffin it will show positive up to 48 hours after ingestion. There was a story of a police officer that got suspended from his jon with no pay, because he ate a Poppy seed muffin the day before. It really matters where the seeds came from.