BACKGROUND/AIM: Cannabis consumption in Germany has been on the rise, culminating in the legalization of recreational cannabis in 2024. This shift aims to minimize the harms associated with black-market cannabis, such as exposure to contaminants, while regulating consumption to reduce health risks. The primary aim of this study is to quantitatively assess the net health effects of cannabis legalization in Germany by balancing harm reduction from fewer contaminants against potential risks from increased consumption.

METHODS: A quantitative projection model was employed to evaluate the potential net health effects of cannabis legalization in Germany. By estimating the likely increase in consumption and corresponding health risks, the study calculated quality-adjusted life year (QALY) losses due to cannabis use disorder (CUD) and long-term health impacts from both cannabis dependence and contamination exposure.

RESULTS: Projected increases in adult cannabis consumption may lead to 400,000-800,000 new users, resulting in approximately 2,300 additional cases of severe long-term mental health conditions. The corresponding QALY losses from CUD-related harms are estimated to be approximately nineteen times greater than the health gains from reduced contamination-related harm. Sensitivity analysis shows that consumption rates have a strong influence on net QALY outcomes, with even a 1% increase in cannabis use sufficient to produce net population-level harm.

CONCLUSIONS: The findings suggest that cannabis legalization in Germany may not achieve the intended health benefits. Increased consumption, particularly among new users, may result in considerable public health burdens, with QALY losses associated with CUD outweighing gains from reduced contamination. Effective regulation and public health interventions are needed to minimize adverse health outcomes while avoiding a resurgence of black-market sales.