Randomly administered drug tests, however, do nothing to further this goal and can actually hinder it. Overlooked in the debate about drug testing is the fact that drug testing has never been scientifically shown to improve workplace safety or productivity. This is most likely because drug tests do not measure current impairment. They can only determine whether metabolites from past drug use are present in the medium being tested. For instance, metabolites from marijuana consumption can be detected in the urine for more than 30 days after the person's last exposure to marijuana.
Hair testing is even more bizarre.
A hair test can detect past drug consumption as far as several years back if the hair is long enough. It is difficult to imagine what possible legitimate use an employer would have for such information. Drug tests do not detect alcohol, our nation's leading drug of abuse. Tests that do detect alcohol are separate, rarely administered, and only detect current impairment. Drug tests do not detect fatigue or stress, the cause of one-third of all workplace accidents.