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THC exposure during pregnancy linked to life-long health risks

The consumption of Tetrahydrocannabinol (THC) during pregnancy could potentially alter the normal course of fetal development, with implications for the lifelong health of the offspring, according to new research from Oregon Health & Science University (OHSU).

Published today in the journal Clinical Epigenetics, this preclinical study has shed light on a topic that has, until now, remained largely shrouded in uncertainty due to a lack of data on the safety of prenatal cannabis use.

Focus of the research

THC, the primary psychoactive ingredient in cannabis, is a substance whose usage and availability are surging across the United States. 

As its popularity rises, so does the prevalence of cannabis use in pregnancy, particularly during the critical first trimester. This is a period when the developing fetus is highly susceptible to environmental influences, with many women resorting to cannabis to alleviate morning sickness. 

However, despite the escalating use, the potential ramifications of prenatal cannabis use on fetal development have not been definitively established.

This pioneering study by the OHSU team aimed to delve into the long-term health implications of THC use during pregnancy. 

Alterations to the epigenome 

The study, conducted in a non-human primate model, found that prenatal THC exposure resulted in alterations to the placental and fetal epigenome – the intricate chemical modifications to DNA that oversee gene regulation and expression. 

These changes, disturbingly, paralleled those seen with several prevalent neurobehavioral conditions, including autism spectrum disorder.

“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. The reality is that cannabis still carries many health risks for certain populations, including those who are pregnant,” said study lead author Dr. Lyndsey Shorey-Kendrick, a computational biologist at OHSU’s Oregon National Primate Research Center (ONPRC).

Dr. Shorey-Kendrick underscores the need to comprehend these impacts more deeply to inform patients about the risks effectively and promote safer habits during the vulnerable prenatal period.

The researchers administered THC in daily edibles to a nonhuman primate model, comparing the results to a placebo group. In particular, the experts investigated the epigenetic changes in key areas signifying healthy prenatal development, including the placenta and the fetal lung, brain, and heart.

Results of the study

The analyses revealed that THC exposure fundamentally altered the epigenome, a process wherein the information encoded in a gene is translated into a function or an observable trait. 

With every gene making up DNA uniquely coded to contribute to various bodily and brain functions, any interference with the epigenetic processes due to drug exposure raises concerns – particularly during a critical developmental period like pregnancy.

Significant changes were observed in genes related to common neurobehavioral disorders such as autism spectrum disorder and attention deficit hyperactivity disorder. Such conditions are associated with unfavorable health outcomes in childhood and adolescence, including impaired memory and verbal reasoning abilities, as well as heightened hyperactivity, impulsivity, and inattention.

Future implications of the research 

The team, including prominent researchers Dr. Eliot Spindel, Dr. Elinor Sullivan, Dr. Owen McCarty, and Dr. Jason Hedges, hopes their findings will improve the limited literature on THC use during pregnancy. The experts also hope to influence patient counseling and the future development of public health policies addressing cannabis.

Study co-author Dr. Jamie Lo, associate professor of Obstetrics and Gynecology at the OHSU School of Medicine, noted that discussing cannabis use is not a common practice among providers dealing with pregnant patients or those attempting to conceive. 

“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,” said Dr. Lo.

The research thus serves as a stark reminder that a deeper understanding of cannabis and its potential effects during pregnancy is a public health necessity.


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