Does xenical give a false positive drug test?

No: I know of no research that shows xenical can cause a false-positive drug test. All xenical does is block some of the fat from your diet from being absorbed, thus decreasing your calorie intake. This shouldn't cause either a urine or a blood drug test to become positive.

No: Many diet pills are stimulants, and are related to (or actually are) amphetamines. Xenical (or the otc version alli) is completely different, and is not even absorbed. It prevents you from absorbing fat, so it only works when you cut way way back in your fat intake. If you don't you get diarrhea with fatty and oily stools. Sometimes you even get "accidents." this forces you to cut back on fat.