Long lasting effects of chronic heavy cannabis abuse

The purpose of this study was to evaluate the extent of short-term memory impairment and schizophrenia-like symptoms in heavy and systematic cannabis users and the association between the severity of abuse and the longevity of its persistent symptoms after refraining from such use.

A complete psychiatric examination and a psychometric evaluation were performed in 48 solely cannabis users. Additionally, head hair samples were analyzed and the detected cannabinoids levels were correlated with the psychometric findings.

A total of 33.3% (n = 16) of the total examined cannabis users were currently imprisoned. The years of abuse ranged from 1 to 35 years and the median daily dose was 5.84.4 gr and 4.84.0 gr for prisoners (n = 16) and non prisoners (n = 32), respectively. A total of 39.6% of the users experienced hallucinations (mostly auditory), 54.2% experienced delusions (mostly ideas of reference and persecution), 85.4% had organic brain dysfunction in a test addressing visual-motor functioning and visual perception skills, and all users (100%) were found to have organic brain dysfunction in a test of visual memory immediate recall. The cannabinoid metabolite levels in the hair samples were consistent with the reported history of substance abuse and total grams of consumption for the participants below 35 years old (p < .001). Statistically elevated cannabinoids levels were observed in users with auditory hallucinations compared to users without any hallucinations (p = .019).

The existence of hallucinations, delusions, and organic brain dysfunction in heavy cannabis users seems to be associated with cannabinoid levels in hair. The continuation of persistent symptoms 3 months after the discontinuation of cannabis abuse, was a remarkable finding.

We provide evidence that chronic and heavy cannabis abuse results in long-lasting brain dysfunction in all users and in long-lasting schizophrenia-like psychotic symptoms in more than half of all users. These findings suggest a reevaluation of the current classification of cannabis as a "soft narcotic" which erroneously, therefore, is typically considered harmless. (Am J Addict 2017;26:335-342).