Like a standard urine test, hair testing can detect substance use for an extended period, providing up to a 90-day history for the most common drugs of abuse. It takes about 90 to 120 strands of hair, according to LabCorp, to run an effective test. Most often associated with marijuana use, hair testing can also detect the use of amphetamines, cocaine, opioids, and phencyclidine (PCP). Employees should be aware that dying the hair, shaving the head, and using detoxing shampoos are not effective ways to beat a hair drug test and when scalp hair is not available, testing can be conducted from areas such as the eyebrows or arms.
