New Study Challenges Beliefs About CBD in Pregnancy, Reveals Unexpected Risks

CBD is gaining popularity as a remedy for pregnancy symptoms like nausea and anxiety, but new research suggests it may not be as safe as many believe.

A study from McMaster University found that oral cannabis use, including both THC and CBD, is linked to impaired fetal growth, abnormal placental development, and long-term behavioral changes in offspring.

CBD Use in Pregnancy: Research Uncovers Potential Risks

Cannabidiol (CBD), a compound in cannabis often used for therapeutic purposes, is becoming increasingly popular among pregnant individuals to help manage symptoms like nausea, anxiety, and sleep disturbances. While many believe that CBD — especially when taken orally — is a safer option, research on its effects during pregnancy remains limited.

A new study from researchers at McMaster University sheds light on this knowledge gap, revealing potential risks linked to both CBD and tetrahydrocannabinol (THC), the psychoactive component of cannabis. The findings suggest that using these substances during pregnancy may impair fetal growth and development.

Published today (February 5, 2025) in eBioMedicine, part of The Lancet Discovery Science, the study found that oral cannabis use from early to mid-pregnancy was associated with restricted fetal growth, changes in placental development, and long-term effects on offspring behavior, including altered aggression, activity levels, and learning ability.

Perception vs. Reality: Is CBD Really Safe?

"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. 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," says Tyrah Ritchie, who led the study while completing her master's degree in the Medical Sciences program at McMaster University and with the McMaster Immunology Research Centre.

Cannabis Use May Impact Growth and Behavior

The group of scientists led by Ritchie and Ali Ashkar, professor with McMaster's Department of Medicine, conducted the research by administering cannabis oil to mouse models and followed the development of the fetuses during pregnancy and post-birth.

The researchers found that both THC and CBD impaired fetal growth causing fetuses to be small when compared to mice that did not receive cannabis. Additionally, they found that both THC and CBD impact the development of the blood vessels that supply the placenta and therefore the baby with nutrients.

"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. 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 growth restriction," says Ashkar.

Long-Term Effects on Offspring Behaviour

When observing the behavior 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 the growth of the baby but seems to have long-term consequences as the babies were found to have changes in their behavior later in life," says Ritchie.

More Research Needed on CBD and Pregnancy

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.

Reference: "The impact of oral cannabis consumption during pregnancy on maternal spiral artery remodelling, fetal growth and offspring behaviour in mice" by Tyrah M. Ritchie, Emily Feng, Fatemeh Vahedi, Sofya Ermolina, Christian J. Bellissimo, Erica De Jong, Ana L. Portillo, Sophie M. Poznanski, Lauren Chan, Sara M. Ettehadieh, Deborah M. Sloboda, Dawn M.E. Bowdish and Ali A. Ashkar, 5 February 2025, eBioMedicine.
DOI: 10.1016/j.ebiom.2025.105572

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.