Heavy Cannabis Use During Pregnancy Linked to Slower Brain Growth in Babies: McGill Study

Heavy cannabis use during pregnancy can lead to delays in fetal brain development that last into adulthood, a new McGill University study has found. AAP Image/Jane Dempster

Heavy cannabis use during pregnancy can lead to delays in fetal brain development that last into adulthood, a new study has found.

McGill University researchers used MRI techniques for brain imaging to track the effects of prenatal cannabis exposure in mice. The results were published in the Molecular Psychiatry journal in September and reported in a Nov. 18 news release from McGill.

The researchers conducted a simulation of daily exposure equivalent to one or two joints containing more than 10 percent Delta-9-tetrahydrocannabinol (THC) during a pregnancy stage comparable to the first trimester in humans.

They found development changes in three life stages, including late pregnancy where babies exposed to THC had smaller bodies and larger brain ventricles. It was a sign of “abnormal brain development,” according to researchers.

The study showed that newborns exposed in utero to cannabis gained weight faster but had slower brain development, “suggesting a mismatch or delay.” Small brain size persisted into adolescence and adulthood, the researchers said. They noted it was especially evident in females, who also exhibited more “anxiety-like” behaviours.

The study adds to current biological evidence regarding the effects of the drug during pregnancy, according to McGill.

The research has a level of detail that is not often achieved in studies, first author Lani Cupo said in the release.

“That’s partly because this type of research is incredibly resource intensive,” Cupo said. “We used live brain imaging to follow development across the lifespan, which isn’t commonly done in mice.”

It also reflects the impact of the higher-potency cannabis currently available, the university said.

Study co-author Mallar Chakravarty said the findings are a step in determining the long-term effects of current THC products.

THC is one of the compounds found in the cannabis plant and causes a high and intoxicated feeling, according to Health Canada.

“Since cannabis legalization is relatively recent, we don’t yet have long-term human data on newer THC products,” Chakravarty said. “Our findings offer an early glimpse of possible outcomes a decade or two down the line.”

Health Canada says the THC potency in dried cannabis has increased from 3 percent by weight in the 1980s to about 15 percent in modern strains, and that some strains have up to 90 percent THC.

Canada legalized cannabis in 2018 with the Cannabis Act, a move the health agency says was a shift from “prohibitive measures” to an “evidence-informed public health and public safety approach.”

Health Canada noted that THC has “some therapeutic effects, but it also has harmful effects, which may be greater when the potency of THC is higher.” It said the adverse effects of the drug can be affected by frequency of use and the consumption method.