A recent study in the UK showed that people who began smoking cannabis during their college years were 90 per cent more likely to display symptoms of psychotic behaviour during their 20s. Individuals that had never displayed any symptoms of this type before could start to experience hearing voices in their head, having paranoid ideas and even display bizarre behaviour, and with prolonged cannabis use can have regular hallucinations. Cannabis addiction can be an issue, but many argue that the benefits of using cannabis overpower the negatives.

Other mental health symptoms could include delusions, disordered thoughts and even schizophrenia. This study, which was conducted by the Institute of Psychiatry in London, officially demolishes previously held beliefs that cannabis use was not responsible for the development of any mental illnesses. There was no evidence however, to show that people suffering from psychotic symptoms would turn to cannabis for relief.

A professor of psychiatry from the Institute of Psychiatry, Sir Robin Murray, says of this most recent study: “It is one of ten prospective studies all pointing in this same direction. In short, it adds a further brick to the wall of evidence showing that use of traditional cannabis is a contributory cause of psychoses like schizophrenia. It adds new information by showing that it is those who show psychotic symptoms within a few years of initiating cannabis use who are especially likely to develop persistent psychotic symptoms if they persist in their use of cannabis.”

Professor Wayne Hall, from the University of Queensland, notes: “The case is strengthened by evidence that regular cannabis use in adolescence predicts poorer educational outcomes, increased risk of using other illicit drugs, increased risk of depression and poorer social relationships in early adulthood.”