Now a days, besides blood, urine, saliva & hair is being recognized as an alternative & fundamental biological specimen for drug testing in the field of forensic analysis & clinical chemistry. Hair testing was used in legal cases, historical researches. This review on methodologically & practically used to the application of hair as a biological indication of drug use & abuse. The mechanism of drug incorporation into the hair were commented. This article include sample (hair) collection, preparation & extraction methods as well as the advanced analytical techniques such as immunoassay, HPLC-CE, GC-LC & GC-MS/MS. The outcome of hair analysis had been review for this categories: drugs of abuse(Opiates, Cocaines. Amphetamine, Cannabinoids) & Benzodizapines, prescribed drugs etc. finally the specific purpose of hair testing was discussed along with their interpretation.