Are there any substances that can cause drug test to show positive?

I only know of 2 substances that show a false positive for cocaine. Ampicillin and amoxicillin. However this is a very rare occurrence.

EDIT: Do not believe Mike. Cocaine is not an opiate!

Unless they use some form of chromatography (to separate the components of a complex mixture) followed by Mass Spectra (to weight the molecule and its breakdown products) and IR Spectra to get a fingerprint of the molecule, then they are guessing.

Its cheaper to use other testing methods, and its good for psych services companies (giving drug abuse treatment to people who won't admitt they have a problem), and even the testing people get repeat business. It also puts dirt on people's records to minimize their life-long potential. (What would young Lincoln do if he had this type of dirt on his record, would he have gotten elected?)

There are any number of medications that can cause a positive drug screen. Many pain relievers are opiate derivatives. If you eat large amounts of certain foods that contain poppy seed, it can create a false positive.