From the Guidelines

Yes, acetaminophen use during pregnancy may affect neural development in infants, particularly increasing the risk of ADHD outcomes.

A comprehensive umbrella review of high-quality evidence suggests that prenatal acetaminophen exposure is associated with an increased risk of ADHD outcomes in children, with a potential dose-dependent relationship 1.
The review found that all included studies reported significant associations between maternal prenatal acetaminophen use and ADHD outcomes, with a risk ratio range of 1.08-1.34 1.
The evidence also suggests that the risk of ADHD outcomes may be higher when acetaminophen is used during the third trimester of pregnancy 1.
Some studies found associations between prenatal acetaminophen exposure and increased risk of ASD outcomes, but the evidence is less consistent for ASD compared to ADHD 1.

The exact mechanisms underlying the association between prenatal acetaminophen exposure and neurodevelopmental outcomes are not fully understood, but may involve the activation of the maternal immune system and fetal endocannabinoid system 1.
Confounders such as maternal fever, pain relief, and psychiatric illness may also play a role in the association between acetaminophen use and neurodevelopmental outcomes 1.

The findings of this review suggest that minimization of prenatal acetaminophen exposure may be necessary to reduce the risk of ADHD outcomes in children 1.
However, it is essential to weigh the benefits and risks of acetaminophen use during pregnancy, as it is often used to relieve pain and reduce fever, which can also have negative effects on fetal development if left untreated 1.

From the Research

The use of acetaminophen (Tylenol) in infants has been widely believed to be safe, but recent studies suggest that it may affect neural development 2.
A systematic review of 3096 papers on the use of paracetamol (acetaminophen) in infants and children found that none of the studies monitored neurodevelopment, despite the drug being widely used in this population 2.
Animal models have demonstrated that cognitive development is sensitive to paracetamol exposure during early development, suggesting that the drug may have long-term neurodevelopmental effects 2.

Studies have suggested that prenatal exposure to acetaminophen may be associated with attention problems in children, particularly when exposure occurs during the second trimester 3, 4.
A prospective birth cohort study found that higher acetaminophen exposure during the second trimester was associated with higher Attention Problems and ADHD Problems scores in children at ages 2 and 3 3.
Another study found that cord plasma biomarkers of in utero acetaminophen exposure were associated with significantly increased risk of childhood ADHD and autism spectrum disorder (ASD) in a dose-response fashion 4.

A study in laboratory rats found that therapeutic doses of acetaminophen, even when co-administered with antioxidants, resulted in long-term behavioral changes, suggesting that the drug may have effects on neurodevelopment even in the absence of oxidative stress 5.
The study found that animals treated with acetaminophen plus antioxidants exhibited increased rearing behavior, an asocial activity, when introduced to a novel conspecific, regardless of their exposure to oxidative stress factors 5.

A review of available data concluded that exposure to acetaminophen induces many, if not most, cases of autism spectrum disorder (ASD), and that the very early postpartum period poses the greatest risk for acetaminophen-induced ASD 6.
The review suggested that nearly ubiquitous use of acetaminophen during early development could conceivably be responsible for the induction of the vast majority of all cases of ASD, and that there is no valid rationale for continued use of the drug in the pediatric population given its risks to neurodevelopment 6.