A new study in Australia finds that marijuana, if used for a long time, will increase the risk of getting hallucinations.

The group of Australian researchers surveyed almost 3,100 adults with an average age of about 20 regarding use of marijuana. The survey showed 18 percent of the respondents have been using the drug for three or less years, 16 percent for four to five years, and 14 percent for six or more years.

Of the people who participated in the survey, 65 had been diagnosed with “non-affective psychosis” or mental conditions such as schizophrenia while 233 of the participants showed at least one sign of hallucination during a diagnostic interview.

The researchers were able to conclude in the study that length of time for marijuana use is related to the risk of mental health issues.

According to them, adults who had six or more years of cannabis use were twice more likely to get non-affective psychosis than those who never used cannabis and four times likely to be delusional. Participants were also made to take the Peters et al Delusions Inventory.

The study also indicates that the longer the interval between cannabis uses, the higher the risk of getting psychotic issues.

The researchers emphasize, however, that the relationship between marijuana use and psychosis is not that simple. People who have started hallucinating early in their life are more prone to use marijuana later which could ultimately increase psychosis.

They concluded that there are still further research to be made to understand the mechanisms and the connections better.

The study will be published on the May issue of the Archives of General Psychiatry. It has already been placed online.