MedWire News: Teenage use of cannabis may be linked to early psychotic-like experiences, researchers warn.

Heavy cannabis use has already been implicated in the development of psychiatric disorders such as schizophrenia, say Dr Jouko Miettunen, from the University of Oulu in Finland, and colleagues.

To examine how its abuse relates to warning signs of psychosis, a mental disorder that can include hallucinations, delusions and incoherent speech, the team studied questionnaire answers from 6298 adolescents in the two northernmost provinces of Finland.

The participants, who were all 15 or 16 years old, were asked about whether they had ever tried marijuana or hashish and if they had any psychotic-like experiences in the past 6 months.

These experiences included feeling something strange or inexplicable was taking place in themselves or in their surroundings, the feeling that they were being followed or influenced in some way, and having thoughts running wild or having difficulty controlling the speed of thoughts.

Overall, 5.6% of those questioned reported having ever used cannabis, and 59 adolescents - 0.9% - said they had used it more than five times.

Teenagers who had tried cannabis had significantly more warning signs of psychosis on average than non-users, the researchers report in the British Journal of Psychiatry.

Further analysis revealed that those who had tried cannabis were 2.79 times more likely than others to experience three or more early warning signs, and the proportion of teenagers with high scores increased with frequency of cannabis use.

The researchers say their findings did not relate to other drug use, childhood emotional or behavioural problems or family background, "supporting the hypothesis that cannabis use may be causal in terms of subsequent psychotic symptoms".