Within Jamaica there is a cultural belief that cannabis use is associated with enhanced creativity, improved concentration  and even improved reflexes . These mythical beliefs have resulted in high rates of cannabis use, particularly among the youth, despite cannabis use being illegal in Jamaica.
A 1987 survey of patterns of substance misuse among post primary Jamaican students identified a 19.8% lifetime prevalence for cannabis use, while a 2000 Jamaican National School’s Survey found the lifetime prevalence to have increased to 26.9% . Research findings have suggested that cannabis use may impair neuro-cognitive functioning [4-6].
However, some researchers have suggested that the residual effects of heavy cannabis use on cognitive functions are reversible, lasting only a few days after cessation .
Results from one longitudinal study found that cannabis use does not have a long-term negative impact on intelligence , while others have found that heavy cannabis users had memory and learning impairments even after six weeks of supervised abstention .
There is a paucity of research on cannabis and neuro-cognitive performance in the Caribbean Region, including Jamaica. Given the widespread use of cannabis and its easy availability for Jamaican adolescents, it is important to identify if there are any neuro-cognitive effects associated with cannabis use, among the youth population. This study therefore investigates whether cannabis use among Jamaican adolescent males will result in lowered performances on neurocognitive tasks.
Metabolites of cannabis in their urine, were excluded from the study. Cannabis users were required to abstain from using for a period of 24 – 48 hours prior to participating in the testing.
Of the 35 participants initially recruited for the cannabis use group, 3 were expelled from school and 2 chose to withdraw from the study. Of the 35 participants in the non-user control group, 3 were excluded from the study because their urine contained metabolites of cannabis. A total of 30 cannabis users and 32 non-users were inter viewed for the study. version 14 (SPSS v.14) and t-tests were conducted to assess if there were any significant differences between the performances of cannabis users and non-users.
The mean age of cannabis initiation in this study was found to be early adolescence as seen in other Caribbean studies [3,11]. As adolescence is the developmental period for
experimentation and risky behaviours, along with the cultural acceptability of cannabis use during adolescence is a cause for serious concern as the adolescent brain is still undergoing neural development and may be susceptible to impairments in neuro-cognitive functioning.
Cannabis users exhibited lower scores on all assessed neuropsychological functions as compared to non-users. However, the greatest mean differences were observed through significantly lowered Verbal Comprehension as well as Digit Span scores. This finding implicates cannabis use during adolescence with impairing the neurocognitive functions of working memory, attention, concentration, mental manipulation, language development and verbal intelligence. Cannabis users also had significantly lower visual, verbal and working memory scores than those of non-cannabis users with the largest differences being seen on the delayed subtests. The observance of significantly lower scores on the delayed subtests implies that the long term memory of cannabis user may be more susceptibility to neurocognitive decline.
Cannabis users had lower scores on all tests of learning, attention and memory than non-users. This is consistent with findings from previous research neuropsychological performance [13-18]. A meta-analytic study by Grant, et al.  also identified impairment in the ability of chronic users of cannabis to recall new information, though findings by Schwartz  and Lyons  indicate an absence of long-term residual effects of cannabis use on cognitive abilities. Traditionally, Jamaicans view cannabis use as providing many benefits. These findings are an important step in providing empirical evidence for possible cognitive impairment from cannabis use, among the adolescent population. Further research is needed to determine dose-related, in addition to long-term residual effects of cannabis use on neuropsychological performance in the Caribbean. Understanding the relationship between the complex factors that influence neurocognitive performance of cannabis users should further help to inform the development of public policy and legislation in Jamaica and the Caribbean.
The sample size of 30 for the user group even though deemed sufficient, was still small and the present study consisted of male participants only. It would be of interest to know if there is a gender difference in cannabis users’ in performance on neurocognitive tests of memory.
The findings suggest that there is a significant difference in performance between Jamaican male adolescent cannabis users and non-users on neuro-cognitive tests. Users of cannabis displayed cognitive deficits on all tests of memory, intelligence, language and attention that were conducted. The present findings lend new support to the notion that cannabis use may impair neurocognitive functioning.
There are implications for poor school performance by adolescent users of cannabis in Jamaica. These results support the need for public health policies aimed at targeting early prevention strategies, demand reduction, identification and treatment of adolescent cannabis users in Jamaica.
Source: Ment Health Addict Res, 2016 doi: 10.15761/MHAR.1000118
Karyl Powell-Booth1,et al