Since the 1990s is it known that there is a relationship between the use of cannabis and schizophrenia spectrum disorders (Thornicroft, 1990). Several psychologists have investigated this relation and have come to different answers regarding its importance. In many countries around the world, the attitude towards the use of cannabis is getting more liberal in recent times. This liberalization of the illegal drug use leads apparently to an increasing trend of cannabis use, especially among adolescents and young adults. Therefore the topic of a relationship between the use of marijuana and hence the onset of schizophrenic disorder has gained new relevance in the science of Psychology. New research about the relationship of cannabis and schizophrenia has been conducted in order to gain more knowledge not only about the connection but also about what actually triggers or at least contributes to the onset of schizophrenia. This paper will deal with the question whether there really is a relationship between the use and abuse of cannabis and the development and onset of schizophrenia and if so, what the relation exactly is. There are five different hypotheses about the relation of cannabis and schizophreniform disorder. The self-medication hypothesis, use of cannabis as result of coping with negative symptoms of schizophrenia; the other drug hypothesis, other drugs taken together with cannabis as cause for later schizophrenia; the confounding hypothesis, relation between cannabis and schizophrenia is caused by a third unknown variable; the interaction hypothesis, cannabis as a trigger cause for schizophrenic disorder only in people who are vulnerable (genetically or another way) to schizophrenia; and the etiological hypothesis, use of cannabis as a unique contributing factor to the onset of schizophrenia (Smit, 2004). This paper will only focus on the latter three hypotheses because the first two have already been disproved. The considered hypotheses are supported by findings of a Swedish historical cohort study (Zammit, Allebeck, Andreasson, Lundberg, & Lewis, 2002) and a Dutch cohort study (van Os et al., 2002). After taking the supporting arguments of a relationship into account the paper will focus on statements of scientists that belief the use of cannabis would be a self-medication method of schizophrenics to relieve their symptoms like depression and to relax. In the end, the paper will conclude that there is a relationship between the use of marijuana and schizophrenia. The three considered hypotheses will be, at least to some point, proven right. However, there has to be much more research done to fully understand the connection and the subsequent implications of cannabis abuse in schizophrenic patients. As the investigation of a connection between schizophrenia and the use of cannabis indirectly searches for the other triggering causes of schizophrenia it will become clear at the end, that the relation examined in this paper is only a little part of the search to determine what causes schizophrenia.
The Relation between Cannabis and Schizophrenia
According to the three hypotheses the paper will consider, there is a relationship between the use and abuse of cannabis and the later break-out of schizophrenia. Zammit et al. (2002) carried out a follow-up study of a historical cohort study of 1969 -1970. Their sample consisted of approx. n=50.000 participants between the age of 29 and 34. These participants had to indicate their life-time cannabis use and how often they used cannabis. In correlation with their psychological medical reports the researchers could back up the hypothesis that there is a relationship. An important aspect of this research was that the group did not have a prior history in psychotic disorders, those who had could not take part in the study. The problem of other substances influencing the development of a...