Noriaki Shima

Purpose: Hair testing for drugs has been used extensively in the forensic field since the 1990s, primarily in cases involving abused drugs such as methamphetamine and cocaine. Since the 2010s, its scope has expanded to include the detection of single dose of hypnotics, aiding in the investigation of serious crimes. This review presents essential knowledge for hair testing and the currently recommended analytical procedures and forensic applications. Methods: A review of literature from the 1990s to the 2020s was conducted, focusing on analytical methods for detecting drugs in hair, drug concentrations in hair, and drug incorporation pathways. Results: The characteristics of hair as a biological specimen include a longer detection window than other matrices such as urine and blood, as ingested drugs remain stable in hair over time. Significant differences in drug concentrations in hair are observed among substances, with several hypnotics, such as triazolam, having extremely low concentrations. Drugs are incorporated into hair primarily through two main pathways (the hair bulb and the upper dermis zone), with the dominant pathway depending on the drug’s properties. In addition, hair dyeing and subsequent exposure to aqueous environments (e.g., daily hair washing) can significantly influence drug concentrations and their distribution patterns (concentration and hair region). These factors must be carefully considered in hair testing. Conclusions: Hair testing is an effective means for proving drug intake and estimating use history, particularly in cases where there is a delay in reporting the incident. The interpretation of results must account for various factors, such as the chemical structures of drugs, incorporation pathways, and hair dyeing.

Hair testing for drugs has been used extensively in the field of forensics since the 1990s as a means of obtaining firm evidence of drug ingestion. In addition to its longer detection windows, hair is the only specimen that can provide chronological information on individual drug use. Illicit drugs and hypnotics account for the majority of substances involved in crimes; they are usually analyzed to prove an addictive use or an exposure to drugs in drug-facilitated crimes. The mechanism of drug incorporation into hair has been intensively investigated to properly interpret the results of hair analysis. However, the exact mechanism remains under much discussion, despite the growing application of hair tests. Recently, the authors have applied matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS) imaging and sectional hair analysis of 1-mm segments using liquid chromatography-tandem mass spectrometry (LC-MS/MS) for single-strand hair, to investigate the incorporation pathways of drugs into hair. Time-course changes in drug distribution along single-strand hair suggest that the incorporation of drugs occurs in two regions of the hair root, the hair bulb and the upper part of hair root, and suggest that incorporation from the hair bulb continues for about 2 weeks. Distribution profiles of different drugs in hair additionally revealed that the main incorporation pathway varies (i.e., via the hair bulb or the upper part of hair root) depending on the properties of the drug/metabolite. These findings should be taken into account upon discussing individual drug-use history based on the results of hair analysis.

In order to obtain fundamental information on the drug incorporation into hair, time-course changes in drug distribution along single-strand hair were observed following a single oral administration of zolpidem (ZP), one of the most frequently-used hypnotics. Quantitative sectional hair analyses of 1-mm segments were performed for each single-strand hair using a validated liquid chromatography−tandem mass spectrometry procedure. ZP was detected in all specimens plucked at 10 and 24 hours after a single dose, and the distribution ranged over the whole hair root (4-5 mm in length). A significantly high concentration of ZP was detected in the hair bulb region, whereas much lower concentrations were widely observed in the upper part of hair root of those samples; this suggested that the incorporation of ZP occurred in two regions, mainly in the hair bulb and to a lesser extent in the upper dermis zone. ZP-positive area formed up to 10-12 mm lengths after single administration, indicating its incorporation from the hair bulb to continue for about 2 weeks. Time-course changes in the ZP concentration in hair root additionally revealed that only a small portion of ZP that initially concentrated in the bulb was successively incorporated into the hair matrix and moved toward the keratinized region as hair grew. These findings should be taken into account upon discussing individual drug-use history based on hair analysis. The matrix-assisted laser desorption/ionization mass spectrometry imaging of ZP in the same kinds of hair specimens was also successfully achieved.