A fingernail drug test is a non intrusive way to obtain a deep history of an individual's past drug use.  But how does fingernail testing work?  When an individual uses drugs those drugs spread throughout the person's body affecting almost every body system.  As the drugs are metabolized, they continue spreading throughout the body via the bloodstream.  Trace indicators of drug use are left behind in a few places, even long after drug use.  One of these places is inside the fingernails and toenails.  By analyzing a person's fingernails for these trace indicators, one can determine whether or not the person has used drugs within the last several months.