Teenage cannabis users are more likely to suffer psychotic symptoms that raise the risk of full-blown mental illness in later life, according to a new study in the British Journal of Psychiatry.

Adolescent drug takers interviewed for the largest study of its kind reported experiencing at least three symptoms indicating a risk of psychosis. More than 6,000 youngsters aged 15 and 16 were involved in the research in Finland.

Symptoms indicating a risk of psychosis included:

- Feeling like something strange or inexplicable was taking place
- Suspecting they were being influenced or followed
- Difficulty in controlling the speed of thoughts

Dr Jouko Miettunen, who led the research at the University of Oulu in Finland, said the findings were significant because they demonstrated a link with psychosis at a very early stage of cannabis use.

One of Cygnet Health Care's consultants, Dr Zerrin Atakan, who has carried out research and written on the effects of cannabis, offers help to those who have such concerns, and says: "The provision of appropriate knowledge delivery on the subject and early intervention are both important to prevent the development of a psychotic illness."

Cygnet Health Care is Britain's leading provider of psychiatric care for patients with psychological, emotional and addiction problems.

www.cygnethealth.co.uk