Different drug tests deliver value in different ways. Mostly related to time.
All drugs are eventually eliminated from the body. They may be eliminated after being metabolized by the body’s organs, or passed through intact. In most cases the kidneys are responsible for eliminating the drugs or metabolites are excreted from the body in urine. The time it takes to eliminate drugs depends on metabolism rate, concentration of liquids and other factors. But most people will excrete drugs or metabolites in a few days.
Because many drugs are water soluble, they tend to be metabolized quickly meaning there is a relatively short window in time when they may be detected by tests that use body fluids as the source for detection. Urine, oral fluids and blood are all testing methods that are sensitive to that metabolization time window. They detect drugs in body fluids for a few days.
Hair is not constrained to a detection window of a few days because the drugs are deposited inside hair and remain there. The window of detection for hair starts with when drugs deposited are accessible above the scalp line—usually 5-10 days—meaning it is not ideal for post-accident or testing-for-reasonable suspicion situations. But to identify a chronic user, or to augment a positive body fluids test result with historical perspective, nothing is better than a Psychemedics 90-day detection window.