This review focuses on basic aspects and recent studies of hair analysis for abused and therapeutic drugs and is discussed with 164 references. Firstly, biology of hair and sampling of hair specimens have been commented for the sake of correct interpretation of the results from hair analysis. Then the usual washing methods of hair samples and the extraction methods for drugs in hair have been shown and commented on. Analytical methods for each drug have been discussed by the grouping of three analytical methods, namely immunoassay, HPLC-CE and GC-MS. The outcomes of hair analysis studies have been reviewed by dividing into six groups; morphine and related, cocaine and related, amphetamines, cannabinoids, the other abused drugs and therapeutic drugs. In addition, reports on stability of drugs in the living hair and studies on drug incorporation into hair and dose-hair concentration relationships have been reviewed. Applications of hair analysis to the estimation of drug history, discrimination between OTC drug use and illegal drug use, drug testing for acute poisoning, gestational drug exposure and drug compliance have also been reviewed. Finally, the promising prospects of hair analysis have been described.