Routine Hair Testing Unmasks Hidden Synthetic Cannabinoid Use in Forensic Psychiatric Patients: A 10-Year Comparative Study in Two Bavarian Clinics

TL;DR

A 10-year study found that hair testing in forensic psychiatric patients revealed much higher use of synthetic cannabinoids compared to urine testing, especially when combined with strict monitoring.

Contribution

The study demonstrates that hair analysis is significantly more effective than urine testing for detecting hidden synthetic cannabinoid use in forensic psychiatric patients.

Findings

Hair analysis detected seven times more synthetic cannabinoid use compared to urine testing in Guenzburg.

Patients with a history of violence were four times more likely to test positive for synthetic cannabinoids.

The stricter monitoring regime in Guenzburg led to a significant increase in the number of tests conducted after 2022.

Abstract

Background: Germany provides a worldwide almost unique legal framework for offenders with substance use disorders through § 64 of the German Criminal Code, mandating a two-year multimodal therapy including an in-house clinical treatment period followed by a reintegration phase with gradually reduced supervision. During this phase, lapses are often concealed, with synthetic cannabinoids (SCs) serving as a potential tool due to limited detection in routine screenings and heterogeneous monitoring practices across forensic psychiatric clinics. Methods: This study compared two forensic hospitals, Guenzburg and Kaufbeuren, over a ten-year period, from 2014 to 2024, to evaluate monitoring strategies. While Kaufbeuren applied a case-dependent testing approach, including unannounced urine screenings, Guenzburg introduced a stricter regime in 2019, combining mandatory hair analysis three months into reintegration with unannounced broad-spectrum screenings including SCs. Results: Among the 527 patients included in this study, significantly more tests were conducted in Guenzburg after 2022. The different approach between hair vs. urine analysis produced a seven-fold higher detection rate of SC use compared to Kaufbeuren. Across both clinics, however, SC-positive patients shared similar features. They were younger at first conviction, more frequently under substitution treatment, and more likely to have committed violent offenses. A history of violence quadrupled SC-positive odds, while time since leave as such increased odds by 0.1% per day. Conclusions: In conclusion, these results underscore the effectiveness of standardized long-term SC monitoring using hair analysis and the predictive role of a history of violence in the context of SC-relapse.

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