But not, it seems, when it comes to cannabis addiction.

A UNE research team analysing studies involving more than 5300 cannabis users internationally has confirmed that four traits - neuroticism, openness, conscientiousness and agreeableness are all implicated in problematic cannabis use. However, it's a problem cannabis user's openness that distinguishes their addiction from that to nicotine, alcohol or even harder drugs like cocaine.

"For this reason, openness may hold the key to effective intervention and treatment for those using high doses of this psychoactive drug," says Associate Professor John Malouff, from UNE's School of Psychology.

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Cannabis is the most commonly used illicit substance in the world and, following its legalisation for medicinal purposes in several countries, considered increasingly acceptable. But one in eight users will develop dependence, lifetime prevalence has risen in most developed countries, and the health risks of addiction have received little attention.

If used to excess, cannabis can cause serious social, physical and psychological effects. Anxiety, depression and acute psychosis are common and cannabis is known to harm the brain, heart, lungs and testes.

Associate Professor Malouff, Associate Professor Nicola Schutte and Alex Winters investigated what personality traits set problem cannabis users apart.

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"Problem use is associated with high openness and neuroticism (being worried, temperamental, self-conscious and moody), and low agreeableness and conscientiousness," says Assoc. Prof. Malouff.

"Most people would see openness to new ideas and experiences as a positive personality characteristic, but it may contribute to people getting into cannabis (to sample the novel psychedelic effects) and trying different types of the drug. Sometimes that openness can lead to seriously harmful behaviour."

People lacking in agreeableness and conscientiousness are problematic for psychologists to treat, however their openness may prove helpful.

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"Cannabis users who are disagreeable and unconscientious are not likely to go to treatment and, if they do, are unlikely to stay in treatment or complete activities recommended by their clinician," Assoc. Prof Malouff says. "However, a greater openness could make them more prepared to explore different forms of treatment and therapy."

The finding that people who are more neurotic are more likely to become problem marijuana users suggests that those people should avoid marijuana entirely, according to Assoc. Prof. Malouff.

"Instead of helping them to feel better, cannabis creates problems on top of their existing problems," he says. "We would want to intervene before those people got hooked."

As our cultural, political and legal landscape changes in response to cannabis use, Assoc. Prof. Malouff says there is a strong need for more research to inform public and medical policy.

"The more liberal a nation becomes on cannabis use, the more people will use it and develop problems," he says. "Our findings suggest a role for personality factors in the treatment and prevention of problem cannabis use. Treatments that help control negative emotions without resorting to cannabis use could be useful for prevention."

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