The literature reviewed shows that many of the analytical problems related to the toxicological analysis of hair have been resolved, but in some cases, as for the application of the extraction methods, it is worth highlighting that the parameters must be carefully valued owing to the different operative options that are documented in the literature. Besides, the choice of a suitable extractive procedure may be influenced by various factors, including the following: (i) the type of drug which the analysis is targeted at and its characteristics of stability in different hydrolytic systems; (ii) ratio of distribution of the abused substances and their metabolites in the hair; and (iii) method used for the subsequent qualitative and quantitative analysis. Hence the selection of the extraction method requires some considerations, particularly when this kind of analysis is used in the forensic field. In this regard, emphasis is actually placed on pharmacokinetic incorporation and retention of drugs into hair. Furthermore, lacking any source of certified reference material, more studies concerning the recovery, accuracy and, if possible, quality control programs, could be implemented in order to test each procedure and improve the reliability of the extraction steps in the toxicological analysis of hair.
