In this study, we delineate trends of cannabis use, offences for possessing minor amounts of cannabis, as well as cannabis-related diagnoses in Germany. Between 2009 and 2021, the estimated number of people using cannabis has increased from about 2.9 to 5.2 million while the number of people with a cannabis-related diagnosis in outpatient medical settings has more than tripled, thus, exceeding the growth of users. Out of the three indicators examined, offences for possessing cannabis have increased the least. Hence, the proportion of cannabis users seeking treatment has increased while the proportion of cannabis users registered to have violated the narcotics law has decreased slightly.
Limitations
Before discussing the implications of these trends and the subnational differences, we want to highlight some limitations. First, the estimates of past-year use prevalence are obtained from two population-based surveys which may considerably underestimate the true prevalence of cannabis consumption [
1]. While population-based surveys do constitute the gold standard in the field, the validity of their estimates is determined by sampling frame and response biases. However, using data from the same surveys with a comparable methodology over time and assuming that the biases do not change substantially over a period of 10 years, we presume that the time trends of our estimates are consistent. Second, for those states without any observed prevalence rates, the estimates rely strongly on the assumption that use prevalence and cannabis-related hospitalisations correlate substantially. Unless any surveys are conducted in those states, we are unable to validate our findings, thus, they should be interpreted with caution. For states with available survey estimates, the imputed values appear to be generally close to the observed data (see Supplementary Fig. 1) thus our assumption of correlating use prevalence and CUD-related hospitalisation appears dependable from a methodological point of view. Third, the rising rate of cannabis-related diagnoses may reflect greater awareness of physicians and psychotherapists or an increased tendency to seeking help on the users’ side. With the data available, we are unable to disentangle these two drivers. Fourth, we do not have detailed information on the extent of synthetic cannabinoid use in Germany, so we are unable to accurately describe the share of cannabis-related diagnoses that reflect chronic use of natural vs. synthetic cannabis products. In the 2017/2018 European Web Survey of Drugs, there were 27,231 persons reporting use of only natural cannabis products contrasting 104 persons who reported using only synthetic cannabinoids (2,567 used both: [
21]). As a sizeable share of European cannabis samples suspected for adulteration do contain synthetic cannabinoids [
28], the number of people who unwillingly use synthetic cannabinoids may be higher than reported by users. In German specialised outpatient addiction care facilities (not part of the analysed data as they are not funded by SHI), only 0.1% of admissions declare “synthetic cannabinoids/other” as main drug in 2021 (compared with 23.3% cannabis: [
40]). Also, UK hospital data show no notable upward or downward trend between 2015 and 2019 [
9]. Acknowledging that the acute use of synthetic cannabinoids is associated with greater adverse somatic consequences than the acute use of natural cannabinoids [
8], we believe that the contribution of synthetic cannabinoids to total cannabis consumption and resulting chronic health problems (cannabis-related diagnoses in outpatient settings) is minor.
Implications
The trends of all three indicators suggest rising cannabis use as well as increasing cannabis-related legal and health problems. Trends regarding rising cannabis use [
29,
41], cannabis-related hospitalisations [
15], and treatment demand in specialised addiction centres [
22] have been described before. Our study adds that the number of persons with cannabis-related diagnoses by physicians and psychotherapists in outpatient medical settings has also increased. In fact, we observe that outpatient cannabis-related diagnoses increased at a faster rate than the number of cannabis users, resulting in a higher proportion of users recognised with use problems. This result is difficult to interpret and there are at least three possible explanations. First, the recognition of problems linked to cannabis use has increased, resulting in a higher number of people seeking help for their problems. However, this would be a German-specific or European trend because opposite patterns were observed in the US with falling numbers of people seeking treatment for cannabis-related problems during periods of rising use prevalence [
25,
26,
37]. It could be argued that the observed increased treatment rates are a consequence of increased police or court referrals, however, in Germany these referrals do not concern physicians or psychotherapists in outpatient settings and treatment rates increased substantially more than offences, so this explanation appears unlikely. Second, increased treatment uptake could be a result of more severe health problems per user. In Germany and most other European countries, cannabis potency has increased modestly for herbal and substantially for resin in the past decade [
22]. Increasing potency levels in turn have been associated with greater health risks [
31] and an observational study has linked variations in potency levels to treatment rates in the Netherlands [
14]. Third, the trends merely reflect changes in the documentation, reflecting increased awareness of health care providers.
Interestingly, the largest increase in cannabis-related diagnoses was observed among older adults, i.e. those aged 35 and over. To some extent, this reflects a disproportionate increase in the prevalence of use in this age group. It is possible that the increasing average age of cannabis users reflects a longer history of use rather than increased initiation among older adults. This is supported by available estimates of age at first use, which have changed little over time (2015: 19.2 years; 2021: 19.4 years) and appear to be only slightly higher among older users (in 2021: 25–29 years: 18.4 years; 50–59 years: 23.8 years; [
32,
35]). According to data from 20–30 years ago, less than 50% of German cannabis users aged 14–24 years stopped using cannabis within 10 years [
30]. Given the available data, it is plausible to assume that a higher proportion of people today continue to use cannabis beyond the age of 30 or 40. There is very little evidence on the long-term effects of (intensive) cannabis use, but the risk of experiencing cannabis-related health problems appears to increase with accumulated exposure to cannabis [
45], such as mild cognitive decline [
24]. Conversely, older cannabis users may also adopt low-risk use strategies to avoid developing cannabis use problems [
19].
Our findings suggest that cannabis use and related offences have risen less than outpatient cannabis-related diagnoses. For offences, we observe a stagnation in the last 2 years, perhaps owing to the COVID-19 pandemic. According to our findings, a sizeable, similar number of people using cannabis is affected by either health (3.7 per 1000 persons aged 15–64) or legal problems (3.1 per 1000 persons aged 12–59). These figures, however, capture only a fraction of persons with cannabis-related health problems (as not everyone with problems seeks help at all or help in the studied settings). Despite most offences may not be linked to severe legal or social consequences, the magnitude of potential legal problems linked to cannabis is not negligible: In Germany, the authorities may choose to not prosecute first-time violations [
12], nonetheless, even the mere possession of minimal amounts of cannabis constitutes an offence against the narcotics law and can lead to a conviction (usually a fine). Moreover, those violations may also result in a suspension of the driving licence, with potential adverse implications for occupational and social life, while racial biases in cannabis arrests have been widely studied [
17] and incarcerations are known to have detrimental health consequences (e.g. [
18,
36]), respective data from Germany are not known to the authors. We can only add that the risk of legal consequences is highest for young male users.
Generally, the sequelae of law violations are still understudied and widely ignored from traditional health perspectives (see for example comprehensive and widely cited literature reviews of cannabis health risks: [
6,
27]). Accordingly, public health indicators to evaluate cannabis policies do usually not consider the extent of legal problems or their (health) sequelae [
13]. Given the extent of cannabis-related law offences in Germany, it appears prudent to consider them in evaluations of law changes [
46].