1.1.1 Backgounds and Objectives Cannabis is the most popular drug worldwide and while 149-271 million people aged 15-64 years use an illicit drug at least once a year, the due of cannabis users is about 125-203 million (World Drug Report 2020). In high-income countries such as United States or Europe, cannabis use typically begins in late teenage years and peaks in the middle 20s as it decreases when young people marry and/or enter worklife (Brodbeck, et al., 2013). However, 10% of people who ever used cannabis, become daily and about 25% weekly users (Hall & Lynskey, 2020). Δ9-tetrahydrocannabinol (THC) is said to be responsible for the psychoactive effects of cannabis. The activation of the endocannabinoid system via CB1 and CB2 also intervenes with the mesolimbic dopaminergic system. This is assumed to be the cause of dependency on drugs while affecting the drug-dependent reward system (Koob & Volkow, 2016). Cannabis dependency is the most common type of drug dependence following alcohol and tobacco with a prevalence of 1-2% of adults per year (Degenhardt, et al., 2019). Cannabis can cause withdrawal symptoms including anxiety, insomnia and depression. Chronic cannabis abuse is said to be a high risk-factor for developing a psychiatric illness like schizophrenia-like psychosis and psychotic symptoms, thereby linking cannabis to the dopaminergic system (Murray, et al., 2017; Di Forti, et al., 2019; Gobbi, et al., 2019; Hasan, et al., 2020; Swapnali & Borah, 2020). The cocaine- and amphetamine- regulated Transcript is said to have a pivotal role in the drug-associated reward system (Hubert, et al., 2008; Kimmel, et al., 2000; Yu, et al., 2017). The role of CART in addiction is underlined by studies showing an upregulation of central CART by chronic misuse of cocaine and other psychostimulants as well as nicotine and alcohol (Chengpeng, et al., 2017; Fagergren & Hurd, 2007; Cho, et al., 2015; O Koylu, et al., 2006; Kaya, et al., 2016; Liu, et al., 2018; Walker, et al., 2021). CART-Gene alterations have also linked this system to Addiction in general (Lohoff, et al., 2008). However, little is known about the effects of Downers like Opioids and Cannabis on CART expression levels (Bakhtazad, et al., 2016; Malboosi, et al., 2020) and so far, nothing has been published on the effects of CART-level in connection with Cannabis. Further, nothing is known about the effects of these drugs on peripheral CART-mRNA and CART-peptides-level alterations in humans. Therefore, the aim of this study was to determine whether there is an effect on these peptides in the peripheral blood of chronic cannabis users, compared to smokers and non-smokers. 1.1.2 Methods and Material The present study was approved by the Ethics Committee of the University of Erlangen-Nuremberg. As 36 subjects suffered from THC dependence, 20 age- and sex-matched cigarette smokers and 21 non-smokers were recruited for this pilot study, in total 77 people. The 36 THC dependent subjects had an established diagnosis of THC dependence according to DSM-V and ICD-10. As assessed with the Symptom Check List SCL-90 (Derogatis, et al., 1976) and a brief physical examination, all of the participants were otherwise physically and mentally healthy. Beyond that, several clinical scales were surveyed: The SWLS was employed to measure satisfaction with life (Diener, et al., 1985). Craving was assessed with a visual analogue scale. The WHO-Assist V3.0 was performed for the assessment of the involvement with alcohol, nicotine and illegal substances such as Cannabis. With the Fagerström Test (FTNA) (Heatherton, et al., 1991) the severity of nicotine dependence was assessed. We took one blood sample after acute consumption of Cannabis and Tobacco and measured Serum CART protein levels using a commercially available enzyme immunoassay (ELISA) kit as well as a polymerase chain reaction kit for the quantitative analysis of CART-mRNA extracted from peripheral white blood cells. Those results were then investigated statistically. 1.1.3 Results and Observations There was a highly significant connection between CART-peptide levels in peripheral serum and CART-mRNA-level in peripheral white blood cells and there were significant differences in these levels regarding the independant groups (Cannabis / Smokers / non-smokers). The level of CART-mRNA and CART-Protein were at highest in non-smokers and lowest in cannabis dependency. Furthermore, the analysis of logistic multiregression could show a prediction model for Craving with respect to CART-mRNA and CART-peptid levels. There was no significant connection between body weight and CART-levels in this population, although a tendency towards a statistical connection could be shown. 1.1.4 Conclusion Our results indicate a direct relationship between CART-mRNA and the CART-protein, consistent for smokers, non-smokers and THC group. Furthermore, these findings suggest an inhibitory effect on CART-mRNA and therefore CART-protein levels in connection to Cannabis exposure. Experimental results supporting CART modulation by chronic drug abuse, raised the hypothesis that CART could play a pivotal role in the molecular vulnerability to substance dependency. As shown for alcohol abuse, the activation of hypothalamic CART neuropeptide, with increased hypothalamic CART levels after ethanol exposure, may be a common mechanism underlying drug-seeking behavior (Dayas et al. 2008). CART has also been linked to the system of energy homeostasis (Lau, et al., 2018). Dysfunction of this circuit with the alteration of central hypothalamic CART has been linked to obesity and eating disorders (Hunter, et al., 2004). Thus, the findings of this study underpin the suspicion of CART having a crucial role in addiction itself and maybe there is a way that peripheral fluctuations of those neuropeptides mirror the effects of central processes connected to addiction. In this context, CART might be a thrilling target for further researches in this area, maybe even as a target for therapy of Addiction and food related health issues.