Effect of chronic marijuana use on cognition: A crosssectional study in urban Bengaluru

INTRODUCTION

Cannabis or Marijuana is a psychoactive drug obtained from various parts of the plant Cannabis sativa. It is one of the commonest recreational drugs, and the most common illegal drug across the globe. Known to produce euphoria or a ‘high’ feeling, this drug has become increasingly popular among the youth and even adolescent age groups.

The active compound in herbal cannabis, D9- tetrahydrocannabinol, exerts all of its known central effects through the CB1 cannabinoid receptors. CB1 receptors are expressed at particularly high densities in the basal ganglia and cerebellum, so it is not surprising that cannabinoids have complex effects on psychomotor function.¹

At doses exceeding the psychotropic threshold, ingestion of cannabis usually causes enhanced well-being and relaxation with an intensification of ordinary sensory experiences. Acute adverse effects caused by overdosing are increased heart rate and changes in blood pressure.²

But chronic effects of this drug is still a fairly research deficit area. Unwillingness of people to openly accept the consumption of an illegal drug is one the main reasons for lack of in-depth studies on this.

In a study conducted in Europe, the prevalence of psychiatric disorders in cannabis users, according to DSM-IV criteria in the sample was high. A current mood disorder was present in 48% and an anxiety disorder in 55% of the cannabis users in the last 12 months.³

The World Drug Report 2019 suggests a continued rise in the number of cannabis users worldwide. This rise is also visible in Asian countries although quantification is difficult due to lack of prior survey statistical data. The prevalence of cannabis use in India is estimated to be about 3% of the population aged 18 years and older and at < 1% in adolescents aged between 10 and 17 years. While this number may appear small, the size of the population in the country would put the absolute numbers at about 4 million individuals. The prevalence of cannabis use disorder in those aged between 10 and 75 years stands at 0.7%. The report further describes bhang as the most common form of cannabis consumption, being driven by cultural practices as well.⁴

India alone carried out 6 per cent of the world’s cannabis herb (“ganja”) seizures in 2016 (nearly 300 tons), and reported seizing even higher quantities in 2017 (353 tons, representing a 20 per cent increase compared with 2016). The figures for 2017 are the highest in India during the period 2013–2018.⁵

Unlike physical effects of the drug, which can be measured by laboratory tests and simple clinical methods, the effects of the drug on cognition and mental health are rather quite difficult to carry out. Studies in this area, especially in India are very scarce.

The Montreal Cognitive Assessment (MoCA) is a screening tool used in the geriatric population to detect mild cognitive impairment.⁶ This has found to be more sensitive in this aspect when compared to the more popular Mini-mental state examination (MMSE). We utilized this screening tool for cognitive assessment in cannabis users.⁷

This study aims to contrast the sociodemographic profile and compare cognitive effects (using the MoCA test) between chronic cannabis users and non-users.

MATERIAL AND METHODS

This is a cross-sectional study conducted in Urban Bengaluru, India between July and September 2016. Due to a lack of prior similar studies, we used a sample size of convenience with a snowball sampling technique.

Males and female students aged between 18 and 25 years, from professional colleges of various streams like medicine, engineering, commerce and arts were included in the study. They were grouped as user if they were chronic cannabis users (operational definition is as below) and as a control if they have never consumed cannabis in any form.

Individuals acutely under the influence of the drug during the study, prior diagnosis of a psychiatric or chronic medical illness, prior detection of cognitive impairment, and those unwilling to consent for participation were excluded from the study.

Operational Definitions:

Chronic cannabis user was defined as an individual who consumed cannabis in any form for three or more days in a week without default for the last six months.

Under the acute influence of cannabis was defined as up to 3 hours following pulmonary assimilation and 12 hours following ingestion.

Sociodemographic data was collected from both cases and controls. The types of marijuana use were categorized as smoking (through a joint or bong), drinking (bhang), and eating (in the form of cake or brownies). Methods used only sparingly (once in a month) were excluded. Time of day was divided into three groups of eight hours each; Morning (from 0600 to 1400), Evening (1400 to 2200), and Night (2200 to 0600). The reasons for use was categorized as peer-pressure, relaxation/ creativity, or stress relief. Multiple options for each of the above variables was acceptable. The MoCA test was then administered in the subject’s preferred language. Instructions on how to complete the assessment was provided by the principal investigator. The assessment was graded based on the defined MoCA administration and grading standards.⁸

A total score of 26 and above out of 30 is considered normal (no cognitive impairment).⁹ The total duration of the exercise was expected to last 10 minutes. The MoCA test has been translated and validated in Kannada and Hindi.⁸

Institutional ethical clearance was obtained (KIMS IEC/UG-32/201)

Confidentiality of the subjects was maintained throughout. The test was performed in private, thus the questions and the subject’s response were heard and noted only by the investigator. The subjects were offered a referral to a health care provider for further management of their drug use.

Statistical Analysis

Data from the study was compiled into Microsoft Excel and statistical analysis was performed on the same platform. The scores for the MoCA test were represented as median and interquartile range. A Mann Whitney U test was use to compare the mean MoCA scores between the controls and cannabis users due to non-normality of data. The confidence interval was set at 95% with an α of 0.05. A two tailed p-value was computed and was considered to be significant < 0.05.

RESULTS

At the end of the study period, a total of 62 individuals were recruited. 31 individuals were grouped as cases and a matching 31 individuals were controls. Each group comprised on 29 males and 2 females.

The Demographic data is depicted in Table 1. The marijuana use data was available for 24 of the participants in the user’s group. All 24 (100%) of the users consumed marijuana via smoking. Additionally, 3 (12.5%) consumed as bhang, and 3 (12.5%) in edible form. The reasons for use were mainly due to peer pressure (14; 58.3%) or for relaxation/creativity enhancement purposes (14; 58.3%). Only 3 (12.5%) of the individuals used marijuana as a form of stress relief. 11 (45.8%) of individuals used during morning hours, 12 (50%) during the evening hours, and 21 (87.5%) during the night hours. Figure 1 describes the pattern of use of marijuana divided by the pre-specified time of day. Two dominant patterns of use can be observed. 9 (37.5%) individuals used during all three categories of the day, and the second pattern where individuals used only during the night hours (10; 41.7%).

Out of the 31 subjects in the user’s group, 16 (51.6%) were found to have cognitive impairment (total score < 26) compared to 3 (9.7%) subjects in the control group.

A Mann Whitney U test showed a significant difference between the total score of the MoCA test in the chronic marijuana user group (Median = 25) when compared to the control group (Median = 28); U = 181, p < 0.001. Among the different categories of the MoCA tool, there was a significant difference between the users group and the control group in the categories of Visuospatial function, Attention and Language as depicted by the Mann Whitney U test shown in Table 2. Correction for multiple analyses was not applied to the above analysis.

DISCUSSION

It was found that significantly more individuals who were chronic cannabis users, to have cognitive impairment than those who have never used cannabis. Among the aspects of the MoCA assessment tool, Visuo-spatial skills was the most affected trait followed by Attention and Language.

Delayed Recall, was not different between the users and control group. However, some studies show that relative to nonusers, cannabis users were found to be impaired in several aspects of real-world memory functioning.¹⁰ A better test for memory is thus probably required for a more accurate measure of the effects of cannabis.

The number of female users in our study was significantly fewer than the number of male users. Reasons for this disparity in sex ratio could be social stigma associated with female drug abuse compared to that of male. The World Drug Report 2019 presents similar numbers.⁴

Similar to other addictive drugs, fewer females than males use marijuana. For females who do use marijuana, however, the effects can be different than for male users. Research indicates that marijuana impairs spatial memory in women more than it does in men, while males show a greater marijuana-induced high.¹¹

The percentage of drug users living in hostels (48%) was higher than the percentage of nonusers (32%). This brings into question the role of a healthy environment, parental supervision and peer pressure, all of which are known to affect the habits of an individual. Based on the questionnaire filled by the subjects, peer pressure and parties were ranked the highest reasons of consumption. This observation agrees with a French study done on cannabis dependent individuals which demonstrated that cannabis dependence in adolescents and young adults is related to great psychological distress. The study emphasizes on the importance of substance use prevention as early as middle school.¹²

In terms of monetary funds (either monthly income or pocket money given by parents), both groups did not show a significant difference. The consumption of cannabis based on the socio-economic class of the individual was not determined due to the small sample size.

The limitations of the study was the small sample size in view of the feasibility and consent. Snowball sampling may have led to a selection bias in the user’s group with regard to common drug dealers and the quality of the marijuana used. The MoCA test is a screening tool and cannot be used to diagnose cognitive impairment. More studies are needed using a battery of neuropsychiatric tests administered by trained psychologists to address the issue of cognitive impairment in marijuana use.

CONCLUSION

There are negative effects of chronic cannabis use on the cognitive levels of the individual; cognition of chronic users being significantly lower than that of non-users. Visuo-spatial skills and attention were two aspects of cognition that were significantly affected, with majority of users being male. Economic independence increased the prevalence of cannabis use, as did absence of parental/ family supervision. Peer pressure was also a major contributor in development of cannabis dependence.

Acknowledgement: The authors would like to thank all the participants for their time and agreeing to participate in the study. The study was accepted by the Indian Council of Medical Research as a student project.

Conflict of interest: nil