Cannabis Ups Schizophrenia Risk

Studies show that regularly smoking hashish or marijuana doubles the risk of developing schizophrenia, said Prof Peter Falkai of the Berlin-based German Society of Psychiatry, Psychotherapy and Neurology.

Tetrahydrocannabinol (THC), the main psychoactive substance in hemp, is said to be responsible for the psychotic effect of cannabis.

Adolescents carry the great risk of lifelong mental illness.

Cannabis consumption advances the onset of schizophrenia in people congenitally predisposed towards psychoses by about eight years - to the age of 17.7, on average.

"Many of those affected have trouble thinking clearly, hear voices talking about them or have delusions," explained Falkai, director of the Department of Psychiatry and Psychotherapy at Saarland University Hospital in Homburg.

"They then delude themselves into thinking they possess superhuman powers or are a religious or political personality," Falkai said.

Less conspicuous behavioral changes can also indicate schizophrenia. Many sufferers display social withdrawal or apathy.

People who smoke cannabis regularly may be at an increased risk of developing depression and schizophrenia in later life, the results of three new studies suggest.

In the first study, researchers looked at 1,600 secondary school students from over 40 schools. Around 60% of the participants had used cannabis by the age of 20 and 7% were daily users.

The Australian study found that young women who used cannabis on a daily basis, were five times more likely to develop depression and anxiety later in life, compared to non-smokers.

Overall teenagers who used cannabis on a weekly basis or more, were twice as likely than non-smokers to develop depression later in life.

The second study clarified earlier findings that cannabis is associated with schizophrenia in later life and that this cannot be explained by the use of other drugs or personality traits.

The results indicate "a potentially serious risk to the mental health of people who use cannabis particularly in the presence of other risk factors for schizophrenia", the Welsh researchers said.

Meanwhile in the third study, researchers in London found that using cannabis in adolescence increases the likelihood of experiencing symptoms of schizophrenia in adulthood, with the youngest cannabis users (determined to be around 15 years of age), at greatest risk.

The findings suggest that cannabis use among psychologically and vulnerable adolescents should be "strongly discouraged".

Four main types of schizophrenia are recognized: the paranoid, characterized by delusions of persecution or grandeur combined with unrealistic, illogical thinking and frequent auditory hallucinations; the disorganized (hebephrenic), characterized by disordered speech and behaviour and shallow or inappropriate emotional responses; the catatonic, characterized by motor inflexibility, stupor, or stereotyped movements along with mutism, echolalia, or other speech abnormalities; and the undifferentiated, a nonspecific type. Schizophrenia seems to occur in 0.5-1% of the general population.

Details of all of these studies are published in the "British Medical Journal".