New Study Links Maternal THC Use to Autism, ADHD

3 min read

July 7, 2023 – Researchers have found that consuming delta-9-tetrahydrocannabinol, or THC, during pregnancy can lead to genetic changes during a baby’s growth in the womb that are consistent with those seen in people with autism spectrum and attention deficit hyperactivity disorders.

The new findings, published Thursday in Clinical Epigenetics, come from experiments conducted on non-human primates by researchers at Oregon Health & Science University. Researchers gave pregnant primates edibles with THC, the psychoactive ingredient in marijuana and cannabis products. They noted that, in places where marijuana and THC products are legal, dispensary workers often recommend the products to pregnant women to alleviate nausea.

“Cannabis is one of the most commonly used drugs and is widely available across the country, so there is a common perception that it’s completely safe to use,” said the study’s lead author Lyndsey Shorey-Kendrick, PhD, a computational biologist at OHSU’s Oregon National Primate Research Center, in a statement. “The reality is that cannabis still carries many health risks for certain populations, including those who are pregnant. If we’re able to better understand the impacts, we can more effectively communicate the risks to patients and support safer habits during the vulnerable prenatal period.”

In their article, the researchers noted that previous studies have linked maternal cannabis use with an increased risk for preterm birth, stillbirth, and low birth weight. Studies in mice have shown that exposure increased anxiety and altered brain DNA in baby mice. Prior research has also shown associations between maternal cannabis use and autism spectrum disorder, ADHD, intellectual disability and learning disorders, and other neuropsychiatric disorders, they wrote.

This latest study sought to understand how THC changes genes during fetal development. Researchers gave a group of five pregnant research monkeys a daily THC edible throughout their pregnancies, and another group of five pregnant monkeys got a placebo. The monkeys gave birth by caesarean section (C-section), and tissue was sampled during the delivery from five places: the placenta, a lung, two parts of the brain, and the heart. They found that THC exposure impacted gene expression in all five tissue types, particularly in the placenta. The placenta tissue from the THC group also showed similarities to human placenta samples previously studied that came from mothers whose babies were later diagnosed with autism.

The primates used in the research, called rhesus macaques, have DNA that is 93% similar to that of humans, and have been used to develop some of the largest medical advances for humans in the world, including vaccines and reproductive treatments, according to summaries from Washington University in St. Louis, MO, and the University of Wisconsin.

“It’s not common practice for providers to discuss cannabis use with patients who are pregnant or trying to conceive,” said researcher and OHSU School of Medicine associate professor of obstetrics and gynecology Jamie Lo, MD, in a statement. “I hope our work can help open up a broader dialogue about the risks of cannabis use in the preconception and prenatal period, so we can improve children’s health in the long run.”