Youngsters who partake in using high-caliber ganja every day from an early age push their first psychotic episode up by a few years, according to a recent study in Schizophrenia Bulletin. The findings signify that the extent, timing, and type of cannabis use can disrupt brain development and increase the vulnerability to developing psychosis.

"This is not a study about the association between cannabis and psychosis, but about the association between specific patterns of cannabis use ... and an earlier onset of psychotic disorders," Dr. Marta Di Forti, who led the research at the Institute of Psychiatry at Kings College, explained to Reuters.

Previous research exploring the link between smoking cannabis and psychosis often runs into a chicken-or-the-egg issue with researchers having to consider the possibility that schizophrenics use cannabis more often to alleviate psychotic symptoms that are already established. Although more cannabis use has been established among people diagnosed with a psychotic disorder like schizophrenia, demographic factors, such as socioeconomic status, further blur this link.

To gain a clearer picture Di Forti and her colleagues assessed 410 patients who were visiting a hospital for the first time for a psychotic episode to measure the association between gender, patterns of cannabis use, and onset of psychosis. The patients were also gauged on their history of tobacco, alcohol, and other illicit drug use.

Patients with a history of cannabis use were found to experience their first psychotic episode at an average age of 28.2 years, which was a little over three years sooner than their counterparts who had never used cannabis before. Further analysis also found that the patients who had begun using cannabis at the age of 15 or younger experienced their first psychotic episode at the age of 27, which was a little more than two years sooner than those who began using it after the age of 15.

The finding that the authors found most striking pertained to the potency of cannabis. Patients who used a relatively strong, highly concentrated “skunk type” of cannabis on a daily basis had the earliest average age of onset of psychosis at 25.2 years, which outpaced non-users by six years. The authors also found that patients who began using cannabis at or before the age of 15 preferred the higher potency marijuana, which was considered to be four times stronger than its lower potency “hash-type”.

Overall, males were found to be more avid users of cannabis and also experienced their first psychotic episode at a younger average age than women — 26 years versus 29 years respectively.

Di Forti’s study supports other work that found a link between substance use and an earlier age of onset of psychotic illnesses. One study in the Journal of The American Medical Association analyzed a compilation of work into this matter and suggested that reducing cannabis use could go as far delaying or even preventing some cases of psychosis — especially when other factors, such as family history and sex, cannot be changed. Even if psychosis is inevitable, the JAMA article concluded, buying another two or three psychosis-free years by abstaining from cannabis (and other substances) could allow for the completion of “important developmental milestones of late adolescence and early adulthood that could lower the long-term disability arising from psychotic disorders.”

With regard to the current study, Dr. Wilson Compton, deputy director of the National Institute on Drug Abuse, considered the question of whether the patients would have experienced their psychotic episode despite marijuana use a “distinction we haven’t figured out yet,” he told Reuters. In the meantime, despite the more lenient marijuana laws in Washington and Colorado pertaining to adult cannabis use, he expects the rule changes will be paralleled by more research that will better understand how marijuana effects mental illness.

Source: Di Forti M, Sallis H, Allegri F. Daily Use, Especially of High-Potency Cannabis, Drives the Earlier Onset of Psychosis in Cannabis Users. Schizophr Bull. 2013.