THC Exposure, Not Cannabis Quantity, Predicts Quality of Life Outcomes: An 18-Month Longitudinal Study of Regulated Cannabis Access in Switzerland.

Curiger J.; Mosandl C.; Meyer M.; Guessoum A.; Herrmann O.; Pichler E.; Vogel M.; Walter M.; Baltes-Flückiger L. · European addiction research · 2026

**Background & Methods** This 18-month longitudinal study enrolled 300 participants in a regulated cannabis access program in Switzerland, with objective purchase tracking through pharmacy-based records. Quality of life was assessed using the EQ-5D at baseline and 18-month follow-up, with additional measurements of THC content, problematic cannabis use (CUDIT-R), and self-reported consumption patterns analyzed via multiple regression. **Key Findings** • Overall quality of life remained stable across the study period (baseline M=0.92, SD=0.18; mean change=0.002, p=0.418), indicating that regulated cannabis access did not lead to deterioration in wellbeing outcomes. • Higher cumulative THC exposure over 18 months (b=-0.003, p=0.048), elevated baseline CUDIT-R scores indicating problematic use (b=-0.001, p=0.030), and increased self-reported consumption amount (b=-0.016, p=0.004) independently predicted lower quality of life at follow-up. • Total cannabis quantity purchased through regulated channels did not significantly predict quality-of-life outcomes (p=0.134), suggesting that THC potency and consumption intensity are more clinically relevant than absolute purchase volume. **Dosage & Administration** Not reported. The study tracked objective THC exposure through pharmacy records but did not standardize or prescribe specific dosing regimens to participants. **Safety & Adverse Effects** Not reported. The study focused on quality-of-life outcomes rather than documenting specific adverse effects or safety events during the 18-month observation period. **Evidence Quality** This study provides moderate-quality evidence as a longitudinal observational analysis with objective purchase tracking, a strength absent in most cannabis research. However, limitations include the reliance on a single regulated access setting in Switzerland, potentially limiting generalizability to other jurisdictions or unregulated markets. The study is described as a "Review" in classification, which may indicate secondary analysis rather than primary data collection. Multiple regression analysis controls for confounders but cannot establish causality. Additionally, the study lacks information on participant demographics, baseline characteristics, or potential confounding variables (e.g., comorbidities, concurrent substance use). The EQ-5D provides global quality-of-life measurement but may not capture cannabis-specific impacts on functioning or symptom-related outcomes. These findings suggest THC potency warrants greater regulatory and clinical attention than absolute consumption volume, with implications for harm reduction frameworks.

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