Large Study Shows Canna Mothers’ Children Have Normal Brains

A recent large-scale longitudinal study found no association between cannabis use during pregnancy and differential neurodevelopmental outcomes in exposed children. The study, published in June in the journal Pediatric and Perinatal Epidemiology, had more extensive controls for confounders than previous studies and followed children up to age 20. When the researchers considered the parents’ traits, the researchers found no associations between prenatal cannabis and neurodevelopmental differences.

This is positive news considering that 4.2% of pregnant women report using cannabis and the number is rising. Pregnant cannabis users also face arrest, imprisonment and deportation of their children in several states.

Prenatal marijuana exposure was not associated with secondary outcomes or risk of clinical deficit in any neuropsychological study.

Oliver G Isik, “Neurodevelopmental outcomes in children after prenatal marijuana exposure,” 2023

Is Cannabis Safe During Pregnancy?

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Cannabis use during pregnancy is still an extremely controversial topic. Some praise the plant’s ability to relieve morning sickness and pregnancy pains. Others worry that the potent mix of chemicals in cannabis could have a negative impact on the developing child. Unfortunately, research on this topic is quite inconsistent.

Some studies show increased neurodevelopmental differences such as ADHD, anxiety and autism in children exposed to cannabis in utero. Others find no connection.

Low participant numbers or weak observational study designs can make it difficult to say whether cannabis actually causes these differences.

For example, a 2020 systematic review found that cannabis use during pregnancy may be associated with ADHD and mood symptoms such as anxiety in the resulting children. Another 2020 study found that children whose mothers used cannabis during pregnancy were 50% more likely to be diagnosed with autism.

But these studies may not stand up to scrutiny. Experts point to problems in the methodology of much of the available research. Low participant numbers or weak observational study designs can make it difficult to say whether cannabis actually causes these differences.

Neurodivergent Children: Cannabis or Parental Factors?

One of the main issues confounding research is whether to account for parental characteristics such as other drug use or pre-existing medical conditions. For example, a 2021 study found no association between autism and prenatal cannabis use when maternal education and alcohol and tobacco use were factored in.

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A 2023 study found that cannabis-exposed children did not have a higher risk of autism when maternal stress (a known risk factor for both childhood autism and cannabis use) was factored in. And a 2021 study of 2,408 children found similar results for ADHD. When confounding factors were taken into account, no associations remained.

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We spoke to the author of this new study about prenatal cannabis exposure

Recent estimates suggest that the heritability of autism—the extent to which autism is passed from parents to children—could be as high as 90%. In ADHD it can be as high as 88%. Failure by researchers to consider whether parents have traits associated with these disorders can seriously skew the study.

This is particularly important as both autism and ADHD are associated with higher levels of substance use, and cannabis can relieve symptoms in both. It may seem that cannabis causes differences in neurodevelopment. However, parents who are more likely to pass on these differences may also be more likely to use cannabis during pregnancy.

Study shows cannabis is not associated with neurodevelopmental differences

The study, published this month by researchers at Columbia University and the University of Western Australia, Perth, was a step ahead of most research on the subject. They chose to control for a wide range of clinical and sociodemographic characteristics of the parents, which helps avoid many of the limitations of previous studies. Their study also extended over a long period of time. Using data from 2,868 children from the Raine study, researchers were able to analyze the course of prenatal cannabis exposure from pregnancy to age 20.

This is a much longer period than most studies have examined.

To achieve this, the children underwent neuropsychological testing at the age of 10 and again at the age of 19 or 20. This is a much longer period than most studies have examined. Combined with a large sample size and more extensive controls, a clearer picture emerges of what actually accounts for prenatal cannabis use.

The researchers found no correlations with these controls. The authors explain: “Children with PME [prenatal marijuana exposure] performed no worse than unexposed children aged 10 years and [again at ages] 19 to 20.”

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Cannabis use during pregnancy: that’s what the science says

Limitations of the study: Cannabis is constantly changing

While this is positive news, the study was not without its limitations. A key factor is the change in cannabis potency and the differences in the way people consume cannabis over the last few decades. This cohort included children born between 1989 and 1992 and may have lower THC exposure than children born today. The study authors conclude that “further research is needed in a more modern birth cohort with a range of neurobehavioral outcomes to further elucidate the effects of prenatal marijuana exposure on neurodevelopment.”

Until we get more conclusive data, experts continue to advise women not to use cannabis during pregnancy.