Teenagers who use cannabis frequently were more likely to have children born preterm when they become parents up to 20 years later, according to a new study.

The research, led by the Murdoch Children's Research Institute and the University of Bristol, found preconception parent daily cannabis use at age 15-17 was associated with increased risk of offspring being born premature or with low birth weight, with the results to have potential implications for the legalisation of cannabis use in Australia.  

The findings, published in Scientific Reports, stated one in four babies born to parents (aged 29 and over) who had used cannabis every day between the ages of 15-17 were preterm or had a low birth weight, compared with one in 20 born to parents with no or lower frequency of adolescent cannabis use. There was little evidence of a link between premature birth and low birth weight and preconception parental cannabis use at other ages, at lower levels of cannabis frequency or tobacco use.

The study of 665 participants followed their tobacco and cannabis use between the ages of 14 to 29 years before pregnancy. The data was drawn from the 2000 Stories Victorian Adolescent Health Cohort Study (VAHCS) and Victorian Intergenerational Health Cohort Study (VIHCS).

MCRI and Deakin University's Dr Elizabeth Spry said few studies of antenatal substance use have considered use prior to pregnancy, despite tobacco and cannabis use most commonly starting in adolescence, with rates seen to peak in young adulthood.

"Frequent adolescent cannabis use is more common in males, a group largely overlooked in public health messaging around substance use and birth outcomes where the focus has been predominantly on antenatal tobacco and alcohol use in women," she said.

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.

"We also need to better understand the contexts and lives of teenagers using cannabis daily, to gain an understanding of the experiences and challenges that might lead to very frequent cannabis use and may also impact later health."

Despite improvements in antenatal care, rates of low birth weight and preterm birth remain high in all countries, affecting over one-in-10 births globally.

Prematurity is a leading cause of neonatal death and those who survive have greater risks for neurodevelopmental disabilities in later childhood, cardiovascular and metabolic diseases in later life, and face greater socio-economic disadvantage. 

Murdoch Children's Professor George Patton said the more cannabis use was studied in teens, the more problematic it looked.

"Given growing political and industry drivers for legalisation of cannabis use in Australia, there is a pressing need for bigger and better research into understanding harms arising from heavy adolescent use," he said.

"As Australian states and other jurisdictions around the world take steps toward decriminalisation, and eventually legalisation, of adult cannabis use, there is need to ensure that the legislative changes do not lead to higher cannabis use in teenagers."

Researchers from the University of Melbourne and The Royal Women's Hospital also contributed to the findings.   

Publication: Lindsey A. Hines, Elizabeth A. Spry, Margarita Moreno-Betancur, Hanafi Mohamad Husin, Denise Becker, Melissa Middleton, Jeffrey M. Craig, Lex W. Doyle, Craig A. Olsson and George Patton. 'Cannabis and tobacco use prior to pregnancy and subsequent offspring birth outcomes: a 20 year intergenerational prospective cohort study,' Scientific Reports. DOI: 10.1038/s41598-021-95460-2

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Professor George Patton, MCRI Group Leader, Adolescent Health

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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.


The study was supported by the Australian Research Council (DP180102447) and the National Health and Medical Research Council (APP1063091; APP1008273; APP1157378). 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); The Royal Children's Hospital Foundation; and the Murdoch Children's Research Institute. GP is supported by an NHMRC Senior Principle Research Fellowship (APP1117873). Research at the Murdoch Children's Research Institute is supported by the Victorian Government's Operational Infrastructure Program. This research was funded in whole, or in part, by the Wellcome Trust 209158/Z/17/Z (LH).