Stuttgart, Germany  - Cannabis users between 17 and 30 years are at greater risk of developing multiple types of personality disorders than non-smokers in the same age group, a German study found.

Cannabis also effects women differently than men, the study published in the German psychiatric journal Fortschritte der Neurologie Psychiatrie found.

Researchers at the Protestant Bethanien Clinic in Greifswald discovered that young men tended to become anti-social or develop borderline personality disorders while women who smoked cannabis often become depressed and insecure.

Of the 99 cannabis users examined, 90 per cent later developed an anti-social personality disorder.

Symptoms included disregard for social norms, reduced or non-existent empathy for other people and an inability to change behaviour despite negative experiences.

One third of the participants in the study had three or more personality disorders.

However, the study could not determine whether using cannabis was responsible for any initial change in their personalities. (dpa)