There are a couple of tests done for drugs and, if the proper sophisticated test is done it's highly unlikely that a false-positive will result. However, the basic THC urine test can occasionally read false-positives for the following substances. This list is supplied from three sources including a free internet souce www.drunkdrivingdefense.com
Ibuprofen (such as found in Advil, Motrin)
Naproxen (Aleve)
Ketoprofen (Found in Orudis KT)
Riboflavin (B2, or Hempseed Oil)
Promethazine (found in Phenergan, Promethegan)
Dronabinol (found in Marinol)
Hope this helps!

