Monkeys Fed THC Have Altered Placentas, Study Finds

Cannabis, if consumed during pregnancy, could perhaps increase the chances of the baby developing autism spectrum disorder (ASD), according to a new study.

Published in Clinical Epigenetics, the study tested the placentas of macaque monkeys that had been fed THC-laced edibles when pregnant. The researchers discovered the THC had affected the DNA found in the placenta and “enriched” the genes associated with autism spectrum disorder (ASD).

The researchers say their findings could help inform public health policies regarding pregnancy and cannabis use.

10 monkeys

To get their findings, the researchers from Oregon Health & Science University supplemented the diets of 10 female pregnant macaque monkeys with either an ordinary cookie (five monkeys in this placebo group) or a THC-laced cookie (five in the THC group). The latter monkeys were unknowingly given increasing doses of THC, up to 2.5 milligrams (mg) per seven kilograms per day.

Near the end of the animals’ pregnancies, the researchers performed cesarean sections. The placentas were removed and lung, heart, and brain tissues were then taken from the fetuses. DNA was extracted from each tissue type and analyzed to determine any epigenetic changes.

The researchers found that the THC had affected (methylated) the DNA of all tissue types, most prominently the placenta. Changes in methylation in the placenta were associated with changes in RNA expression in genes enriched for tissue development and morphogenesis-related processes.

In all tissues, loci (locations of genes in DNA) differentially methylated with THC were “enriched” for candidate ASD genes.

Furthermore, the researchers say there was “significant overlap” between these genes and those in human placentas from pregnancies where the newborn was later diagnosed with ASD.

ASD has been linked to hundreds of genes that can affect communication and social cognition. It’s thought the way these genes are affected by the environment (epigenetics) plays a key role in the phenotypic expression of ASD, particularly in prenatal and early years.

Given their findings and THC’s potential link to fetal autism development, the researchers behind the macaque study hope their results can help guide medical pregnancy counselling and public health policies regarding cannabis.

“It’s not common practice for providers to discuss cannabis use with patients who are pregnant or trying to conceive,” Jamie Lo, an associate professor of obstetrics and gynecology at the Oregon Health & Science University School of Medicine, said 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.”

Cannabis and autism

The study isn't the first to link prenatal cannabis use with ASD. Published in Nature Medicine in 2020, one study of birth registry records found that the incidence of ASD diagnosis was 4.00 per 1,000 person-years among children with documented cannabis exposure compared to 2.42 among unexposed children.

While this avenue of research continues to probe the connection between cannabis and ASD development, another is investigating whether cannabis chemicals like CBD can treat ASD. 

Writing in Analytical Cannabis last year, Dr. Karen Litwa and Dr. Ken Soderstrom – an assistant professor of Anatomy and Cell Biology at East Carolina University’s Brody School of Medicine and an associate professor of Pharmacology and Toxicology at East Carolina University’s Brody School of Medicine, respectively – explained this area of research in detail. 

They explained how the brain’s endocannabinoid system (ECS), which can be regulated by cannabinoids, is involved in ASD development, and how they demonstrated this link in a petri dish experiment. 

"Our objective here was not to find a treatment for ASD but to begin unraveling the complex role of ECS activation in brain development and offer a glimpse into a potential treatment target for ASD in the CB1 receptor," they concluded in their article.

"There is still much to uncover about cannabinoids as a cause and a treatment for ASD. For sure, this is an active area of research that will generate rich insight into the interconnection between ECS and ASD. One day, this work could lead to a more complete understanding of its pathogenesis and the discovery of effective cannabis-derived treatments for the condition."

Resources on autism spectrum disorder can be found at the UK's National Autistic Society.

*This article was updated on July 18, 2023, to include references to the work of Dr. Karen Litwa and Dr. Ken Soderstrom and links to resources on autism spectrum disorder. Previous sentences discussing other studies that detailed the rise of prenatal cannabis use among pregnant people in the US were also removed.