Frequent cannabis use by young people linked to decline in IQ

January 28, 2021

Thursday, 28 January 2021: A study has found that adolescents who frequently use cannabis may experience a decline in Intelligence Quotient (IQ) over time. The findings of the research provide further insight into the harmful neurological and cognitive effects of frequent cannabis use on young people.

The paper, led by researchers at RCSI University of Medicine and Health Sciences, is published in Psychological Medicine.

The results revealed that there were declines of approximately 2 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 6 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," commented senior author on the paper Professor Mary Cannon, Professor of Psychiatric Epidemiology and Youth Mental Health, RCSI.

"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.

The study was carried out by researchers from the Department of Psychiatry, RCSI and Beaumont Hospital, Dublin (Prof Mary Cannon, Dr Emmet Power, Sophie Sabherwal, Dr Colm Healy, Dr Aisling O'Neill and Professor David Cotter).

The research was funded by a YouLead Collaborative Doctoral Award from the Health Research Board (Ireland) and a European Research Council Consolidator Award.
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About RCSI University of Medicine and Health Sciences

Ranked number one globally for Good Health and Well-being in the Times Higher Education (THE) University Impact Rankings 2020, RCSI University of Medicine and Health Sciences is an international not-for-profit university, with its headquarters in Dublin.

RCSI is exclusively focused on education and research to drive improvements in human health worldwide. It is among the top 250 universities worldwide in the World University Rankings (2021) and its research is ranked first in Ireland for citations. RCSI has been awarded Athena Swan Bronze accreditation for positive gender practice in higher education.

Visit the RCSI MyHealth Expert Directory to find the details of our experts across a range of healthcare issues and concerns. Recognising their responsibility to share their knowledge and discoveries to empower people with information that leads them to better health, these clinicians and researchers are willing to engage with the media in their area of expertise.

For more information, please contact:

Jane Butler, Senior Communications Officer, RCSI University of Medicine and Health Sciences janebutler@rcsi.ie| +353 87 7531877

RCSI

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