The $2 field drug test kit:
use a single tube of a chemical called cobalt thiocyanate, which turns blue when it is exposed to cocaine. But cobalt thiocyanate also turns blue when it is exposed to more than 80 other compounds, including methadone, certain acne medications and several common household cleaners.
The $10 field drug test kit:
https://www.forensicmag.com/article/2015/05/field-drug-tests-confuse-candy-meth-cause-serious-concern
The videotaped tests showed that mundane items found in supermarkets, including coffee, aspirin, chocolate and oregano, can come up positive for narcotics using the most common tests available to law enforcement. Even Mucinex DM, an over-the-counter cough medication, came up positive for heroin and morphine, they said.
