According to a study released on Saturday, the longer people use cannabis, the more likely they are to experience hallucinations, delusions or suffer from psychosis.

The study discovered that those who first used cannabis when they were 15 or younger were twice as likely to develop a “non-affective psychosis,” which includes schizophrenia.

John MacGrath, from the University of Queensland in Australia, led the research, which was published in the Archives of General Psychiatry.  The study was conducted on 3,801 people with an average age of 20 years old.

“Among all the participants, a longer duration since the first time they used cannabis was associated with multiple psychosis-related outcomes,” the study said.

Of the people studied, 17.7 percent reported using cannabis for three or fewer years, 16.2 percent for four to five years and 14.3 percent for six or more years.

The study said that 65 were diagnosed with “non-affective psychosis,” such as schizophrenia, and 233 had at least one hallucination.

“Individuals who had experienced hallucinations early in life were more likely to have used cannabis longer and to use it more frequently,” it said.

The report said that the relationship between psychosis and cannabis were complex.

It said that people that we vulnerable to psychosis “were more likely to commence cannabis use, which could then subsequently contribute to an increased risk of conversion to a non-affective psychotic disorder.”

Previous studies have also found an association between cannabis use and psychosis, but there were concerns that research had not adequately accounted for confounding variables.