Caps Off to Abstinence: Unraveling Synthetic Cannabinoid Contamination in Hair Analysis With Headgear Evidence?

Hair analysis is widely used to retrospectively monitor long‐term drug exposure in forensic toxicology, yet the possibility of external contamination can complicate result interpretation. This challenge applies not only to common drugs of abuse but also to synthetic cannabinoids (SCs), one of the largest groups of new psychoactive substances (NPS) on the European drug market. During abstinence control, a suspect's scalp hair sample taken in August 2023 was found positive for MDMB‐4en‐PINACA (15 pg/mg) along with several other prevalent SCs, for example, ADB‐BUTINACA, EDMB‐PINACA, and JWH‐210, despite a claimed 2‐year abstinence period. A multi‐matrix, multi‐method analytical approach was applied to the scalp hair, washing solutions, and a cutout of the baseball cap worn during and after the alleged period of SC use, comprising gas chromatography–mass spectrometry (GC‐MS) and liquid chromatography‐quadrupole time‐of‐flight mass spectrometry (LC‐QToF‐MS) screening and liquid chromatography–tandem mass spectrometry (LC‐MS/MS) quantification. The cap extract showed an identical SC profile to the hair sample, with MDMB‐4en‐PINACA at approximately 22 ng/cm 2 . No SCs introduced to the European market after the claimed beginning of abstinence (end of July 2021) were detected. Nicotine, caffeine, and their metabolites verified cap wearing. Hair analyses in our lab since mid‐2021 identified MDMB‐4en‐PINACA as the most prevalent SC (34.8% of positive samples). Thus, contamination of hair by wearing the cap is assumed to be the cause for the presence of SCs in hair. Laboratories engaged in hair analysis for abstinence testing should be aware that drug detection in hair could also result from external contamination by clothing.