Parental Cannabis Use Tied to Child Psychosis Risk

Liam Davenport

April 11, 2018

FLORENCE, Italy — Both mothers and fathers who use cannabis during pregnancy are more likely to have children who experience psychotic symptoms, new research suggests.

An analysis of more than 3500 families showed that maternal cannabis use was linked to a 38% increased risk for psychotic symptoms in offspring at 10 years of age; cannabis use among fathers was associated with a 44% increased risk.

Led by Koen Bolhuis, MD, Department of Child and Adolescent Psychiatry, Erasmus Medical Center, Rotterdam, the Netherlands, the investigators also found there was a similar association with offspring psychotic symptoms and maternal cannabis use both before and after pregnancy.

They conclude that these findings demonstrate "that maternal and paternal cannabis use were each associated with offspring psychotic symptoms at age 10 years, well before the risk period of adolescent cannabis use initiation."

The findings were presented here at the Schizophrenia International Research Society (SIRS) 2018 Biennial Meeting.

Noting that the impact of maternal and paternal cannabis use was comparable, the investigators say this suggests that "common etiologies, rather than solely causal intrauterine mechanisms, underlie the association between parental cannabis use and offspring psychotic symptoms, shedding potential new light on the debated causal path from cannabis use to psychosis."

They believe that "diagnostic screening and preventive measures need to be adapted for young people at risk for severe mental illness," and they offer a family-focused approach.

Family Vulnerabilities

To determine whether parental cannabis use during pregnancy increases the risk for psychotic experiences in offspring, the team studied participants in the Generation R Study, a population-based birth cohort from Rotterdam, the Netherlands.

They included 3692 individuals for whom data on maternal cannabis use during pregnancy, assessed via self-report and the presence cannabis metabolites in urine, were available.

Paternal cannabis use was determined via self-report and maternal report. The presence of psychotic experiences in the offspring was assessed via self-report when the child was aged 10 years.

The team found that 183 mothers used cannabis; 98 did so before pregnancy, and 85 did so during pregnancy. In addition, 386 women continued tobacco smoking during pregnancy. Cannabis use was reported by 297 fathers.

On multivariate analysis that took into account various sociodemographic and psychiatric confounders, maternal cannabis use was associated with a significantly increased risk for offspring psychotic experiences (odds ratio [OR], 1.38; P = .031).

Analyzing cannabis before pregnancy and during pregnancy separately, the ORs were 1.39 (P = .097) and 1.37 (P = .145), respectively, indicating a similar degree of association for both time points.

Curiously, paternal cannabis use was also significantly associated with offspring psychotic experiences at 10 years of age (OR, 1.44; P = .002).

Bolhuis told Medscape Medical News that it is "very difficult to say anything about cause and effect with these kinds of observational analyses."

Nevertheless, he said that the finding that maternal and paternal cannabis use were both associated with psychotic experiences in the offspring "kind of rules out the intrauterine effect of cannabis use on fetal neural development."

Instead, it points to vulnerabilities occurring within a family.

"Parents and pregnant mothers who use cannabis are not a random selection of the population; they are characterized by higher psychopathology scores and lower socioeconomic backgrounds, and we think that those vulnerabilities, whether they are genetic or environmental, get passed onto the next generation," Bolhuis said.

"We know from previous studies that psychotic experiences are indicative of not only psychotic disorder developing later in life but also suicidal ideation and lots of other severe mental health outcomes later. So, somehow, I think this study underscores how bad things in mental health cluster within families, and they can get transmitted to next generation," he added.

Future research efforts, he said, should focus on an earlier stage in childhood development, rather than in the late adolescent period or early adulthood.

"I think we should start to focus on the precursors of mental health, the prodromes of not only psychosis but also severe mental diseases, like major depression or bipolar disorder and suicide ideation, much earlier in life, because these risk indicators can be seen quite early on."

Biologically Plausible

Commenting on the findings for Medscape Medical News, Richard Saitz, MD, MPH, chair and professor, Department of Community Health Sciences, Boston University School of Public Health, Massachusetts, said that he hesitates "to draw any firm conclusions," because few details of the study have been provided and the study has not been fully peer reviewed.

"For example, we do not know how many children experienced psychotic symptoms, nor do we know what potential confounders were adjusted for, and the differences between the adjusted and unadjusted models seem minimal, which could either suggest there is little confounding to worry about, or that the right confounders were not included," he said.

Saitz also pointed out the only statistically significant association was for cannabis exposure overall, rather than specifically before or during pregnancy, "so it leaves further work to be done to sort out the timing."

He noted that although there is "biological plausibility for the association, at least for exposure during pregnancy...the question is whether the association is causal."

Noting that some people will conclude from the study that the association is causal, Saitz continued: "If there is no strong rationale for exposing oneself to cannabis, the safest course would be to not do so.

"However, it is also possible that the findings are not causal; it might be that people who used cannabis and had offspring with psychosis were more likely to remember and/or report cannabis use.

"It is also possible that families in which cannabis is regularly used also expose children to other risk factors for psychosis that may not have been sufficiently addressed in the analysis," he said.

Nevertheless, in summary, Saitz said that the study is "important," in that it is prospective in nature "and seems to have solid methods.

"It is the best type of study to inform the question, since we will never randomize pregnancies to cannabis exposure...unless and until cannabis is studied as a medication during pregnancy. Other studies will need to confirm the results so that we can be more confident in them," he added.

The study was funded with grants from the Netherlands Organization for Scientific Research, Erasmus University Rotterdam, Erasmus Medical Center, and the Netherlands Organization for Health Research and Development. The investigators and Dr Saitz have disclosed no relevant financial relationships.

Schizophrenia International Research Society (SIRS) 2018 Biennial Meeting. Poster F33, presented April 6, 2018.

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