How smoking cannabis can affect your intelligence: Using the drug once a week for six months can knock off two IQ points and could have ‘significant effects’ on teens’ verbal skills
- Researchers analysed data on more than 6,000 teenagers to track cannabis use
- Of the cohort in the study 808 used cannabis at least weekly for six months
- They found those regularly using cannabis as a teenager saw a two point IQ drop
- When it comes to verbal IQ – linked to reasoning – there is a three point IQ drop
Teens who smoke weed at least once a week for six months can lose up to two IQ points as they get older and find it harder to problem solve, a new study revealed.
The Royal College of Surgeons in Ireland (RCSI) studied 808 teens who used cannabis at least weekly for at least six months and 5,308 who did not use the drug.
They discovered that regular dope smokers suffer a decline of two IQ points over time compared to those who did not use cannabis during their teen years.
Further analysis showed that verbal IQ, linked to understanding concepts, abstract reasoning and memory, declines by three points among those who get high.
‘Loss of IQ points early in life could have significant effects on performance in school and college and later employment prospects,’ said senior author Mary Cannon.
The Royal College of Surgeons in Ireland (RCSI) studied 808 teens who used cannabis at least weekly for at least six months and 5,308 who did not use the drug (stock)
Cannabis is the most frequently used illicit substance worldwide, with young people the most common users, according to the team behind this new research.
In the UK alone 29.6 per cent of people aged 16-59 said they had used the drug at least once in their lifetime – up from 23.6 per cent in 2002.
MRI scans taken as part of the study also revealed that those who smoked weed – even minimal incidental use while a teenager – showed evidence of reduced grey matter in the brain.
Study first author Dr Emmet Power, Clinical Research Fellow at RCSI, said there was a clear association between frequent or dependent cannabis use and IQ change.
‘This corresponds to a 1.98-point decline in IQ,’ Dr Power said of the results.
‘We extracted verbal IQ change effect sizes from four available studies This corresponds to a decline of 2.94 verbal IQ points.
They discovered that regular dope smokers suffer a decline of two IQ points over time compared to those who did not use cannabis during their teen years (stock)
Teen marijuana smokers with mental health disorders THREE times more likely to self-harm, study warns
Teenagers with bipolar disorder or depression who smoke cannabis are at increased risk of death and self-harm, a shock new study has found.
Mood disorders in adolescence have long been linked with cannabis abuse and this addiction has now been found to have an impact on mortality.
Researchers from Ohio State University found teens with a mood disorder and a cannabis habit are 3.28 times more likely to self-harm.
‘We found that young people who use cannabis frequently or dependently by age 18 have declined in IQ at follow up and this may be due to a decline in verbal IQ.
‘All studies showed point estimates of IQ decline,’ Power added.
Researchers used data from a number of studies, which limited the available detail as all but one only followed people up to the age of 18 the other one went until 38.
The two point decline in IQ is ‘not to be clinically significant’ and is unlikely to completely explain a range of psychosocial problems linked to cannabis, he said.
Dr Power added: ‘Cannabis use during youth is of great concern as the developing brain may be particularly susceptible to harm during this period.
‘The findings help us to further understand this important public health issue.’
Professor Mary Cannon, senior author and professor of psychiatric epidemiology, said previous studies have shown people who use cannabis regularly when young have worse outcomes in life than non-cannabis users.
Adding that they ‘are at increased risk for serious mental illnesses like schizophrenia.’
She said this small drop in IQ points could lead to significant effects on performance in school, college and life generally which could then result in limited employment prosecutes.
The findings were published in Psychological Medicine.
‘INTELLIGENCE QUOTIENT’ (IQ) IS A MEASURE OF MENTAL ABILITY
IQ stands for Intelligence Quotient and it is used to measure mental ability.
The abbreviation ‘IQ’ was first coined by psychologist William Stern to describe the German term Intelligenzquotient.
Historically, IQ is a score achieved by dividing a person’s mental age, obtained with an intelligence test, by their age.
The resulting fraction is then multiplied by 100 to obtain an IQ score.
An IQ of 100 has long been considered the median score.
Because of the way the test results are scaled, a person with an IQ of 60 is not half as intelligent as someone with an IQ of 120.
The arrangement of IQ scores also means that results are ‘normally distributed’, meaning just as many people score either side of the average.
For example, the same amount of people score 70 as people who score 130.
Although the accuracy of intelligence tests is somewhat disputed, they are still widely used.
For Mensa, the acceptance score requires members to be within the top two per cent of the general population.
Depending on the IQ test, this can require a score of at least 130.
Famous people’s IQ scores:
- Albert Einstein and Stephen Hawking – 160
- Donald Trump – 156
- Emma Watson – 138
- Arnold Schwarzenegger – 135
- Nicole Kidman – 132
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