Hair analysis can detect drug use for approximately 90 days after usage of drugs. Temporary abstention won't beat the test. 

Hair testing cannot be avoided as urine analysis can.  This is because the drug remnants stay permanently stuck in the hair for approximately 90 days. Evidence of drug use cannot be washed or bleached out of hair. 

An unnoticeable snip of hair is easily collected without causing embarrassment to a patient. Collection can be done in-house saving the time, inconvenience, and the cost of having a someone visit a urine collection site.