Scientists have confirmed that prenatal cannabis exposure alters specific genetic markers in the placenta. These markers are strongly linked to a higher risk of schizophrenia in children. The findings appear in Biology of Reproduction, published in January 2026. They add real weight to concerns about what happens to a baby when a mother uses cannabis during pregnancy.

Professor Daniel Hardy led the study at Western University’s Schulich School of Medicine and Dentistry in Canada. His team was the first to show that THC, the main psychoactive compound in cannabis, triggers changes in placental genes already flagged as predictors of schizophrenia risk. Cannabis use in pregnancy is rising. That makes these findings urgent.

Why Prenatal Cannabis Exposure Is a Growing Concern

Canada legalised cannabis in 2018. Since then, use among pregnant women has climbed. Around 5% of pregnant women in Canada now report using cannabis daily. In some communities, the figure is far higher. One study found that 36% of pregnant Inuit women used cannabis, based on self-reports. Among pregnant teenagers aged 13 to 19, one survey recorded a rate as high as 24%.

The most common reasons cited for cannabis use in pregnancy are anxiety, nausea, and insomnia. Many women see it as a natural alternative. But this research makes clear that what feels like a coping tool can cause harm that travels from mother to child before birth.

What Researchers Discovered About Prenatal Cannabis Exposure

The team used a preclinical rat model. Pregnant animals received edible THC mixed with food from gestational day 7 until near birth. The researchers chose this method deliberately. It reflects how many people consume cannabis today, through edibles rather than smoking.

Rat pups born to mothers given THC showed reduced fetal weight. That is a sign of fetal growth restriction. The mothers showed no significant change in food intake, weight gain, or litter size. This detail matters. The harm reached the offspring without any visible signs in the mother.

Researchers then examined the placentas of these pups. They found significantly altered expression in seven genes already linked to schizophrenia risk in humans. Three of those genes, Furin, Rccd1, and Atp5mk, changed in both male and female offspring. Four others, including Eif5, Rps10, Vps33b, and Iqgap1, changed only in female offspring. This points to sex-specific effects that may explain why schizophrenia often presents differently in men and women.

By adulthood, the THC-exposed rats showed decreased prepulse inhibition (PPI). PPI is a neurological test used to assess schizophrenia risk. A lower PPI score means the brain struggles to filter out irrelevant stimuli. Clinicians use this same test in humans. It is one of the most reliable behavioural markers for schizophrenia.

From Rats to Human Cells: Cannabis Use in Pregnancy Under the Microscope

The team then tested whether these findings applied to humans. They treated isolated human placental cells known as BeWo cells with THC for 24 hours. Several of the same schizophrenia-linked genes changed in the same direction seen in the rat model. This lends direct relevance to human biology.

The team pushed further. They used patient-derived brain organoids, which are miniature brain-like structures grown from stem cells. Some came from healthy donors. Others came from people diagnosed with schizophrenia. THC exposure during an early developmental window increased expression of the gene FURIN in both groups.

FURIN is a protein-cleaving enzyme. It activates important brain growth factors, including BDNF, which plays a key role in neuropsychiatric health. FURIN responded to THC across every model in this study. That consistency makes it a strong candidate as an early clinical biomarker for schizophrenia risk. Without such a marker, doctors currently cannot flag risk until symptoms emerge, often between ages 16 and 30.

The Placenta as an Early Warning System for Prenatal Cannabis Exposure

The placenta-brain axis sits at the heart of this research. The placenta does far more than carry nutrients. It produces neurotransmitters, shapes brain development, and appears to record what a baby was exposed to during gestation.

Around 500 genes in the placenta connect to schizophrenia outcomes. Researchers have prioritised roughly 20 of these as key markers. They link to both fetal growth restriction and schizophrenia risk. This study found that prenatal cannabis exposure activates several of those same markers.

If these results hold in larger human trials, placental testing after birth could become a routine way to identify babies at elevated risk. Early identification opens the door to closer monitoring and timely support, years before any psychiatric symptoms appear.

Cannabis Use Before Pregnancy: A Risk Factor Too

One of the more unexpected points in Professor Hardy’s commentary concerns fathers. Pre-conception health in both parents can affect the placenta. Cannabinoid use by either parent before pregnancy may therefore influence placental health and increase schizophrenia risk in the child. Research on this is still in early stages, but it broadens the conversation well beyond the nine months of pregnancy.

What the Research Does Not Yet Answer

This study focused on THC and placental genes tied to fetal growth restriction. Cannabidiol (CBD), the non-psychoactive component of cannabis, has not yet been studied in this context. Researchers also do not yet know whether these same markers can predict other outcomes such as autism or broader cognitive difficulties.

The team acknowledges that large randomised human trials are the next step. Confounding factors such as socioeconomic status and use of alcohol or tobacco will need careful control. Notably, some of the identified biomarkers, including Vps33b, Eif5, Rps10, Furin, and Atp5mk, affect protein secretion. They may one day be measurable in umbilical cord blood, making clinical screening even more practical.

The Broader Picture

Schizophrenia affects around 1% of the Canadian population. It shortens life expectancy and seriously disrupts daily life. Early diagnosis leads to better outcomes, yet reliable early biomarkers do not currently exist. This research brings that possibility closer.

Legalisation has not made cannabis use in pregnancy safer. The biology does not change with the law. Prenatal cannabis exposure occurs during some of the most sensitive windows in human development. The evidence now points clearly in one direction. For anyone who is pregnant or planning to become pregnant, avoiding cannabis is the safest choice for the child.

Source: dbrecoveryresources