Could paracetamol in pregnancy really cause ADHD?

In October's ADC, Archivist reported a study that showed an association between maternal consumption of paracetamol (acetaminophen) and behavioural problems in their offspring, asking whether the link could in reality be due to unexplored confounding factors rather than direct causation (doi:10.1136/archdischild-2016-311708). Coincidentally, a study from the UK has addressed just this question and concluded that there could be a genuine causal link (Stergiakouli E, et al. JAMA Peds 2016. doi:10.1001/jamapediatrics.2016.1775). The long-running Avon Longitudinal Study of Parents and Children (ALSPAC) enrolled 7800 mothers in 1991–2 and asked them about their paracetamol use at 18 and 32 weeks of pregnancy. Behavioural problems in their children at age 7 years were identified by the Strengths and Difficulties Questionnaire. As in previous studies, children exposed to paracetamol had small but significantly increased risks of conduct problems and hyperactivity (risk ratios around 1.3 to 1.4). To test whether some undefined factor which might make women both take paracetamol and also tend to have children with these problems, they went further and looked at post-natal maternal paracetamol use: there was no association with abnormal behaviour in the children. Genetic factors which might be responsible …