HAIR FOLLICLE TEST
Hair drug testing is becoming popular nowadays because of its astounding accuracy than any other drug test. the results are harder to cheat than other tests which you can use synthetic powders and drugs to manipulate the results. Not only that, heavy metal hair test is incredibly easy to conduct.
You only need a strand whether in the person's hair or body to conduct a test. You won't have to worry about invading someone's privacy issues. Hair test can only detect the presence of the following drugs in your body:
Cocaine and metabolites
Opiates (codeine, morphine, 6-acetylmorphine)