According to the study in Florence, Italy, both mothers and fathers who use cannabis during pregnancy are more likely to have children who experience psychotic symptoms

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 ten years of age; cannabis use among fathers was associated with a 44% increased risk.

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."

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, where available.

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

The team found that 183 mothers used cannabis; 98 did so before pregnancy, and 85 did so during pregnancy. Also, 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; = .031).

Analyzing cannabis before pregnancy and during pregnancy separately, the ORs were 1.39 (= .097) and 1.37 (= .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 ten years of age (OR, 1.44; = .002).

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."

"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 individually before or during pregnancy, "so it leaves further work to be done to sort out the timing."

"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.

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