Drug residue remains in hair longer than in bodily fluids. A hair drug test provides a 90 day window of drug use. It doesn’t indicate current impairment due to drugs, only past use. A hair drug test does not detect alcohol use.
Hair drug testing is the least invasive of the types of tests that measure drug use because it only requires a small sample of hair for the testing. Hair can be tested for cocaine, marijuana, opiates, methamphetamine, and phencyclidine.