A new study by researchers from Royal College of Surgeons in Ireland has found that adolescents who frequently smoke marijuana may experience a decline in Intelligence Quotient over time.
The findings of the research, experts say, provide further insight into the harmful neurological and cognitive effects of frequent cannabis use on young people.
The findings, published in the journal Cambridge Core, revealed that there were declines of approximately two IQ points over time in those who use cannabis frequently compared to those who didn’t use cannabis.
Further analysis suggested that this decline in IQ points was primarily related to reduction in verbal IQ.
The research involved systematic review and statistical analysis on seven longitudinal studies involving 808 young people who used cannabis at least weekly for a minimum of six months and 5308 young people who did not use cannabis.
In order to be included in the analysis, each study had to have a baseline IQ score prior to starting cannabis use and another IQ score at follow-up. The young people were followed up until age 18 on average, although one study followed the young people until age 38.
“Previous research tells us that young people who use cannabis frequently have worse outcomes in life than their peers and are at increased risk for serious mental illnesses like schizophrenia.
“Loss of IQ points early in life could have significant effects on performance in school and college and later employment prospects,”
said Senior author of the study and Professor of Psychiatric Epidemiology and Youth Mental Health, RCSI, Prof Mary Cannon.
“Cannabis use during youth is of great concern as the developing brain may be particularly susceptible to harm during this period.
“The findings of this study help us to further understand this important public health issue,”
said Dr Emmet Power, Clinical Research Fellow at RCSI and first author on the study.
Reacting to the study, a Clinical Psychologist at the Department of Psychiatry, Lagos University Teaching Hospital, Id-Araba, Dr. Juliet Ottoh, told PUNCH that cannabis brings about ill motivation among its users.
Ottoh, however, queried the claim about decline in IQ relative to marijuana use.
“If the person has been an intelligent person, cannabis cannot make the individual not to be intelligent. But it will make that person not to function well.
“It only brings about ill motivation, which affects users and makes them not to attend classes. It makes them not interested in their studies. But when they stop using it, they can go back to their functioning.
“But at that moment that it is being taken, it does not allow them to do the right thing. So, it affects their education. For those that are working, it also affects their work,”
According to her, the use of cannabis among youths has become a public health concern, especially in Nigeria. The psychologist said,
“It is a public health concern because if you look at our society, it is porous. Cannabis is now sold everywhere and people are taking it without knowing the health consequences.
“It exposes them to a lot of illnesses. It brings about psychosis, which makes them to act abnormally; it also brings about other mental illnesses such as schizophrenia.
“Some of the youths that you see in the streets stripping themselves are as a result of use of cannabis. People who ought to be doing well are not doing well because they are exposed to the use of cannabis.”
Authors of an article published in PubMed Central said that the rate of cannabis use by young people approximately doubled during the 1990s, perhaps tracking a more general rise in youth disaffection and disturbance.
According to the authors, approximately half of those who use cannabis more than once monthly exhibit behavioural or emotional difficulties.
“Cannabis misuse may itself be associated with harm. For instance, in keeping with frontal cortex effects, intoxication is linked with impaired vigilance, ability for complex thought, memory, and other changes.
“In keeping with these neuropsychological effects, among older adolescents, compared to measurements prior to initiation of use, there is evidence of a small drop in overall IQ”
the authors said.
They said the adverse effects linked to cannabis have increased in recent times.
The World Health Organisation says cannabis is globally the most commonly used psychoactive substance under international control.
It notes that in 2013, an estimated 181.8 million people aged 15−64 years used cannabis for nonmedical purposes globally.
According to the world health body, there is a worrying increasing demand for treatment for cannabis use disorders and associated health conditions in high- and middle-income countries.