A new study from McMaster researchers uncovers potential risks — including impaired fetal growth — in the use of Cannabidiol (CBD), as well as tetrahydrocannabinol (THC), the primary psychoactive component of cannabis. 

CBD, the component in cannabis often used for therapeutic treatments, is used during pregnancy to manage nausea, anxiety and trouble sleeping. Though the public perception is that CBD – particularly when consumed orally – is safer and helpful for symptom management, little was previously known about the impact of CBD on pregnancy. 

The new research, published this week in eBioMedicine, part of The Lancet Discovery Science, finds oral cannabis use from early to mid-pregnancy was associated with impaired fetal growth and changes in the placenta, and affects aggression, activity levels and learning ability in offspring.  

“The use of cannabis during pregnancy is rising in Canada. Most previous studies focus on exposure to cannabis smoke or just the psychoactive component of cannabis (THC), leaving other cannabis ingredients and methods of consumption understudied,” says Tyrah Ritchie, who led the study while completing her master’s degree in McMaster’s Medical Sciences program and with the McMaster Immunology Research Centre. 

“However, consuming cannabis orally or only using other cannabis ingredients like CBD, is often perceived as safer despite this lack of evidence. Our study is shedding light that there’s a possibility that CBD might also be harmful in the pregnancy.” 

Cannabis use may impact growth and behaviour 

The group of scientists, led by Ritchie and professor Ali Ashkar from the department of Medicine, conducted the research by administering cannabis oil to mouse models and followed the development of the fetuses during and after pregnancy. 

Both THC and CBD impaired fetal growth causing fetuses to be small when compared to mice that did not receive cannabis, the researchers found.  

Additionally, both THC and CBD impact development of the blood vessels that supply the placenta — and therefore the baby — with nutrients, they found.  

“We did see that both THC and CBD can disrupt a special type of immune cell called a Uterine NK Cell that is crucial in normal development of the placenta,” says Ashkar.

“We also saw poor development of the arteries that help supply blood to the placenta. We’re thinking this is what is possibly disrupting the nutrient and oxygen delivery to the baby and contributing to the intrauterine grow restriction.” 

When observing the behaviour of the babies post-birth, researchers found changes in their aggression, activity levels and even learning ability.  

“Oral use of THC and CBD during the pregnancy not only disrupts growth of the baby but seems to have long-term consequences as the babies were found to have changes in their behaviour later in life” says Ritchie.  

Ritchie says more research is needed to better understand the impacts of cannabis in humans during pregnancy, but says this study shows the possibility of it being dangerous or harmful.  

Funding for the study was provided by the Michael G. DeGroote Centre for Medicinal Cancer Research, the Canadian Institutes of Health Research, and the Canadian Foundation for Innovation.