Purpose <p>This study evaluated the applicability of segmental hair analysis using liquid chromatography-tandem mass spectrometry (LC/MS/MS) to determine the cause of death in highly decomposed corpses, where collection of urine or blood samples was impossible.</p> Methods <p>Multiple hair samples were collected from a highly decomposed female corpse and cut into 1-, 3-, and 10-mm segments. Qualitative LC/MS/MS analysis was performed on the hair root and shaft segments, followed by detailed quantitative analysis of the hair fragments.</p> Results <p>Qualitative analysis detected the prescribed drugs including zolpidem in all segments, indicating a distribution pattern of daily drug intake. Detailed segmental analysis revealed zolpidem concentrations ranging from 30 to 70 pg/mm in the root segment, and from 200 to 400 pg/mm in the other segments. These findings ruled out a large intake of zolpidem immediately prior to death. Similarly, no evidence of acute overdose with other prescribed drugs was identified.</p> Conclusion <p>This study demonstrated that even in decomposed corpses, where conventional biological samples are unavailable, high-sensitivity LC/MS/MS analysis of hair segments, including the root, enables accurate determination not only of the deceased’s routine intake of sleep-inducing drugs but also of immediately pre-mortem drug intake.</p>