what kind of test is it? the 'dip stick' one? it wouldn't be cost effective to add opiates to bud so i'd rule that out. when i was on probation and tested monthly i constantly tested positive for cocaine in my urine but was always clean on blood tests. and cocaine has been nowhere near me for over 20 years now...so go figure. but if this test is threatening your peace of mind or wallet i'd demand a gas chromagrophy (sp?) test...

i'm sure you'll get it figured out...good luck