A new German-language study provides the first robust longitudinal data on cannabis consumption behavior following partial legalization in Germany. Lena Hahn, Gil Konz, and Kai Sassenberg from the University of Trier surveyed 605 adults one month after the Cannabis Act came into force and again six months later. The result contradicts one of the central assumptions in the legalization debate. There is no notable increase in consumption visible in this sample.
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A longitudinal study at the right time
The work was published under the title „Change and Antecedents of Cannabis Consumption After the Legalization of Recreational Cannabis in Germany“ in the „Journal of Drug Education,“ a peer-reviewed academic journal published by Sage. It ranks among the first quantitative studies to track German consumption behavior not through retrospective reconstruction but through direct observation at two measurement points. The first survey was conducted in May 2024, approximately four weeks after the Cannabis Act came into force on April 1, 2024. The second wave followed six months later, in late autumn 2024.
The sample comprises 605 adult participants from Germany. Data were collected using standardized scales and tested against an established social psychological model. Hahn conducts research at the Social Influence Lab in the Department of Psychology at the University of Trier; Sassenberg additionally leads a department at the Leibniz Institute for Knowledge Media in Tübingen. The connection between both institutions is relevant in context. It represents a social psychological rather than addiction or medical perspective on consumption behavior.
Theory of Planned Behavior as framework
The authors frame their analysis with Icek Ajzen’s Theory of Planned Behavior. This model connects three factors with concrete behavior. A person’s attitude toward the behavior, the perceived subjective norm in their social environment, and perceived behavioral control act through intention on actual behavior. In the context of a policy change such as partial legalization, this framework is particularly revealing. It allows for decomposition of whether an increase in consumption would be driven more by shifted attitudes, changed norms, or improved access.
In the evaluation, shortly after legalization, there is a tight connection between attitude, subjective norm, intention, and perceived control on one hand and reported consumption on the other. This pattern is methodologically expected but politically instructive. It suggests that consumption following the reform was less a reflex to the law than a result of stable attitudes expressing themselves in a now-altered legal environment.
No measurable boom in consumption figures
The politically most important finding is simultaneously the least sensational. Between the two measurement points, no systematic increase in self-reported cannabis consumption can be demonstrated. The concern that the reform would lead to substantial increased use within a few months finds no empirical foundation in this sample. The result fits into a series of international findings that similarly documented stability rather than sudden growth in comparable liberalization phases. A DIW study on consumption patterns in Germany’s legalization phase already traced a similar line, seeing stability in cannabis while documenting markedly more striking increases in cocaine.
Hahn, Konz, and Sassenberg nonetheless formulate clear prevention policy recommendations. Even without a boom in the overall population, prevention programs should remain and specifically reach vulnerable groups. These include adolescents, young adults with family history of substance use, and consumers with pre-existing mental health conditions. The study provides no intervention recommendation for the general population but rather a sharpening of target groups. This emphasis fits a debate that in Germany has thus far oscillated between broad deterrence and targeted risk education, as the CanG interim report of April 2026 extensively documents.
The study’s political weight
The methodological scope of the investigation is limited. A convenience sample of 605 persons across two measurement points does not replace a representative longitudinal survey by the Robert Koch Institute or the Epidemiological Drug Survey. Precisely for this reason, however, the study’s temporal position is relevant. It provides the first longitudinal data for a time window in which robust representative findings from major official surveys are still pending. Until those are available, such pilot findings are the only empirical yardstick against the political narrative of comprehensive consumption boom.
The finding has immediate consequences for three ongoing debates. First, for discussion of adjustments to the Cannabis Act, whose main argument has been a claimed increase in consumption for months. Second, for tightening telemedicine regulations, which are justified with a similar argumentative pattern, as our analysis of the telemedicine discussion shows. Third, for the international assessment of the German reform, as the NIH study on the effect of cannabis legalization on opioid poisonings similarly demonstrates that reforms often work differently than predicted.
Research gaps the study makes visible
Hahn, Konz, and Sassenberg address the antecedents of consumption, but they do not measure the harm side, such as traffic accidents, treatment entries, or cannabis-induced psychosis. This gap is methodologically unavoidable but politically important. A complete assessment of the reform requires interlinking consumption data with routine data from healthcare and justice systems. Early hints from older observational studies, such as on study-related consumption behavior, can be found in our earlier reporting. A complementary perspective is provided by, for instance, the study on cannabis consumption in academic environments. Evidence regarding adolescents also exists, which plays a role in the debate about protective distances, such as in research on cannabis retailers near schools.
For the study’s next survey wave, three points would be particularly interesting. A larger sample with demographic quotas would increase statistical power at the population level. An additional wave after twelve and 24 months would reveal possible delayed effects. A linkage with consumption forms, such as flower, edibles, or vape, would answer whether the reform changed substitution patterns without raising consumption prevalence. A contextualization of the broader legal framework within which these data must be read is provided by the comprehensive overview of the Cannabis Act 2026.
Frequently asked questions
Who conducted the study?
Responsible are Lena Hahn, Gil Konz, and Kai Sassenberg from the University of Trier, with additional affiliation to the Leibniz Institute for Knowledge Media in Tübingen. The work was published in the peer-review journal „Journal of Drug Education“ by Sage publishers under DOI 10.1177/00472379261430434.
How large was the sample and when were measurements taken?
605 adult persons from Germany participated. The first survey was conducted approximately one month after the Cannabis Act came into force; the second six months later, in autumn 2024. Both waves captured attitudes, norms, perceived behavioral control, and self-reported consumption behavior.
Has cannabis consumption in Germany increased following legalization?
Not systematically in this sample. The data show no demonstrable increase in self-reported consumption between the two measurement points. This does not exclude individual changes in subgroups but directly contradicts the narrative of comprehensive consumption boom immediately after the reform.
Why do the authors recommend continuing prevention despite the absence of increased consumption?
Because prevention makes sense before a consumption boom occurs. The study identifies attitude, norm, and behavioral control as central leverage points. These can be specifically addressed especially in vulnerable groups, such as adolescents or consumers with pre-existing mental health conditions. It is precisely there that programs have the greatest impact.
What is the study’s significance for political debate?
It does not replace a representative survey but provides the first longitudinal data immediately following the reform. Those wishing to adjust the reform based on a claimed increase in consumption must henceforth factor these data into argumentative space. Robust figures from the Epidemiological Drug Survey and Robert Koch Institute are still pending.
Hat die Legalisierung deinen Cannabis-Konsum verändert?
Sources: Hahn L., Konz G., Sassenberg K. (2026). „Change and Antecedents of Cannabis Consumption After the Legalization of Recreational Cannabis in Germany.“ Journal of Drug Education. DOI 10.1177/00472379261430434. Profile page of the Social Influence Lab at the University of Trier for Lena Hahn.
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