(Reuters Health) - Cannabis use by mothers or fathers during pregnancy, or even only before pregnancy, is associated with an increased risk of psychotic-like episodes in their children, a Dutch study suggests.

FILE PHOTO: Various-sized joints for sale are pictured at the annual 4/20 marijuana event at Sunset Beach in Vancouver, British Columbia, Canada, April 20, 2017. REUTERS/Jason Redmond/File Photo

Because pot use by mothers and fathers carried similar risk, and a mother’s use before pregnancy had the same effect as use during pregnancy, the study team speculates that parental pot use is likely a marker for genetic and environmental vulnerability to psychotic experiences rather than a cause, and could be useful for screening kids at risk for psychosis later in life.

Babies exposed to cannabis in the womb do have an increased risk of being underweight and unusually small when they’re born and developing cognitive and behavior problems early in life, the researchers note in Schizophrenia Research. Cannabis can also cause hallucinations in adults, particularly with frequent use and at high doses, but less is known about the potential for infants exposed to the drug in the womb to develop psychotic-like symptoms.

For the study, researchers examined data from questionnaires asking 3,692 10-year-olds whether they had symptoms that are similar to what adults might experience with psychosis: hearing voices that nobody else detects, seeing things others don’t see, and having thoughts that others might find strange.

They also examined mothers’ reports on their own marijuana use as well as any use by their partners, and they also looked at lab tests for signs of cannabis in mothers’ urine.

When mothers used marijuana during pregnancy, children were 38 percent more likely to have these psychotic-like symptoms than the children of mothers who abstained from use during pregnancy, the study found. But children of mothers who used pot only before, but not during, pregnancy also had a 39 percent higher risk than the kids of mothers who didn’t use it.

Fathers’ cannabis use during pregnancy, meanwhile, was associated with a 44 percent greater likelihood of psychotic-like experiences in their kids.

“Some children with psychotic experiences are at increased risk to develop psychosis or other psychiatric disorders,” said lead study author Dr. Koen Bolhuis, a researcher at Erasmus Medical Center Rotterdam in the Netherlands.

“Unfortunately very little is known about how to treat psychotic experiences in children, or to prevent them from getting worse,” Bolhuis said by email.

Psychotic-like experiences aren’t disabling or frequent enough to be classified as psychosis, a severe mental health disorder in which patients’ thoughts and emotions are impaired on such a regular basis that they routinely experience delusions and hallucinations that make it impossible to know what’s real and what isn’t.

Psychosis can be caused by schizophrenia, and it can also happen as a result of some other medical conditions and as a side effect of certain prescription medications or illegal drugs.

In the current study, mothers who used cannabis during pregnancy were more likely than other women to smoke and drink during pregnancy, which can both independently influence the risk of emotional and behavioral health problems in children. They were also more likely to have partners who used cannabis while they were pregnant.

The study wasn’t a controlled experiment designed to prove whether or how cannabis exposure might directly cause psychotic experiences in children.

Researchers also lacked data on how much of infants’ cannabis exposure came from parent’s smoking versus ingesting pot.

With inhaled cannabis, it’s difficult to separate the impact of the drug itself from the effect of carbon monoxide also released in the smoke, noted Marcel Bonn-Miller of the University of Pennsylvania Perelman School of Medicine in Philadelphia.

“Carbon monoxide is a known toxicant which causes hypoxia, or oxygen deprivation, which has several well-known and well-studied detrimental effects on pregnancy and offspring development,” Bonn-Miller, who wasn’t involved the study, said by email.

Still, the current study results add to evidence that there’s no safe amount of cannabis exposure for babies in the womb, said Dr. Nathaniel DeNicola of George Washington University in Washington, D.C.

“We have sufficient data and biologic plausibility that marijuana use during pregnancy increases the risk of preterm birth and growth restricted babies,” DeNicola, who wasn’t involved the study, said by email. “The data is mixed on stillbirth, but still cause for concern.”

SOURCE: bit.ly/2n3QYnv Schizophrenia Research, online July 6, 2018.