Newswise — Teenagers who use cannabis frequently may be more likely to have children born preterm, when they become parents up to twenty years later, finds a new University of Bristol-led study. The research, published in Scientific Reports, repeatedly assessed 665 participants in a general population cohort on their tobacco and cannabis use between ages 14 to 29 years, before pregnancy.

The study, led by academics at the University of Bristol in collaboration with the Murdoch Children's Research Institute in Australia, is the first to identify that frequent adolescent cannabis use may also carry intergenerational risks

Maternal tobacco or cannabis use in pregnancy is linked to babies being born preterm and having low birth weight, raising the risks for health problems in these babies.  Substance use in pregnancy tends to be a continuation of use that started before pregnancy, raising a question of whether use in pregnancy or before could be associated with a baby’s early growth.  The collaborative research team used the prospective cohort from the Australian Victorian Adolescent Health Cohort Study (VAHCS) and Victorian Intergenerational Health Cohort Study (VIHCS), with parents recruited to the study when they were in secondary school and followed up until they started having children in their late 20s and 30s; their children were then recruited into a new study.

The researchers found babies born to parents (aged 29 and over) who had used cannabis every day for a period of time between the ages of 15-17 were estimated to be considerably more likely to be born preterm or to have a low birth weight, when compared to babies born to parents who hadn’t used cannabis as teenagers. This effect was limited to people using cannabis at the highest levels of frequency.

The findings are the results of a 20-year prospective study, following parents from their teenage years into their 30s, which found that 20 per cent of all preterm births to study participants occurred in parents who had used cannabis daily during their teenage years.       

Dr Lindsey Hines, Research Fellow in Bristol Medical School: Population Health Sciences (PHS) at the University of Bristol, said: “Cannabis is the most commonly used illicit drug amongst teenagers. There is already evidence that frequent adolescent cannabis use increases the risks for poor mental health, but our results indicate there may be further effects that individuals may not anticipate.

“As regulations around legal use liberalise, there is a possibility that adolescent use may increase in some countries. These findings provide additional motivation for ensuring that policy changes do not lead to greater adolescent use.”

George Patton, Professorial Fellow in Adolescent Health Research with the University of Melbourne and Murdoch Children's Research Institute, added: “The more we study heavy cannabis use in the teens, the more problematic it looks. Given growing political and industry drivers for legalisation of use, there is a pressing need for bigger and better research into understanding harms arising from heavy adolescent use.”

This is the first study to use a prospective cohort to explore associations between pre-conception substance use and birth outcomes, and the findings need to be tested in other samples.  Given the study’s participants were both mothers or fathers of the babies and that heavy teenage use is most common in boys, these findings are particularly important for males.

Further research is needed to compare outcomes for men and women, as well as to understand the biological mechanisms or social conditions that might drive these associations. 


‘Cannabis and tobacco use prior to pregnancy and subsequent offspring birth outcomes: a 20-year intergenerational prospective cohort study’ by Lindsey A Hines, George Patton et al published in Scientific Reports.

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Notes to editors:

Dr Lindsey Hines is funded by the Wellcome Trust.

The study was supported by the Australian Research Council (DP180102447) and the National Health and Medical Research Council.  Data collection for VIHCS was supported by the National Health and Medical Research Council; Australian Rotary Health; Colonial Foundation; Perpetual Trustees; Financial Markets Foundation for Children (Australia); Royal Children’s Hospital Foundation; and the Murdoch Children’s Research Institute.

About the MRC IEU The MRC Integrative Epidemiology Unit (IEU) at the University of Bristol conducts some of the UK's most advanced population health science research. It uses genetics, population data and experimental interventions to look for the underlying causes of chronic disease. The unit exploits the latest advances in genetic and epigenetic technologies. We develop new analysis methods to improve understanding of how our family background, behaviours and genes work together. Using these to investigate how people develop and remain healthy or become ill.

About MCRI

The Murdoch Children's Research Institute (MCRI) is the largest child health research institute in Australia committed to making discoveries and developing treatments to improve child and adolescent health in Australia and around the world. They are pioneering new treatments, trialling better vaccines and improving ways of diagnosing and helping sick babies, children and adolescents. It is one of the only research institutes in Australia to offer genetic testing to find answers for families of children with previously undiagnosed conditions.


Issued by the University of Bristol, UK