Children of mothers who use cannabis during pregnancy appear to be at higher risk of being autistic, according to a study of half a million women. In the largest study of its kind, researchers found four in 1000 children whose mothers used cannabis during pregnancy showed incidence of autism, compared to 2.42 among those whose mothers didn’t use it. Canada has legalised cannabis use but recommend not to consume it if you are pregnant or breastfeeding.

Headline should read: “Retrospective data analysis interpreted to imply a possible relationship after statistical tinkering.” While this comes from a legit paper, the implication of causality in the headline is problematic. From the actual paper: “We use matching techniques to control for confounding and Cox proportional hazards regression models...” This is neither an experimental study, nor an obvious, straightforward difference. Further, even if there is a 1.5 odds ratio, it could run the other way: “Mothers with loading for autism spectrum disorders more likely to be identified as cannabis users while pregnant.”