[Bond]

Here's some more information, but it's still rather vague:

"Zammit and colleagues from the University of Bristol, Imperial College and Cambridge University examined 35 studies that tracked tens of thousands of people for periods ranging from one year to 27 years to examine the effect of marijuana on mental health.

They looked for psychotic illnesses as well as cognitive disorders including delusions and hallucinations, bipolar disorder, depression, anxiety, neuroses and suicidal tendencies.

They found that people who used marijuana had roughly a 40 percent higher chance of developing a psychotic disorder later in life. The overall risk remains very low.

For example, Zammit said the risk of developing schizophrenia for most people is less than 1 percent. The prevalence of schizophrenia is believed to be about five in 1,000 people. But because of the drug's wide popularity, the researchers estimate that about 800 new cases of psychosis could be prevented by reducing marijuana use.

The scientists found a more disturbing outlook for "heavy users" of pot, those who used it daily or weekly: Their risk for psychosis jumped to a range of 50 percent to 200 percent."