Use of acetaminophen during pregnancy is not associated with an increased risk of autism or ADHD in children, according to an analysis of health records involving over 120,000 children. However, a separate study suggests that prenatal exposure to the drug may lead to fertility issues in daughters later in life.
Acetaminophen, the active ingredient in Tylenol, is the only over-the-counter pain and fever reliever advised for pregnant women. Alternatives like ibuprofen have been linked to birth defects, and concerns have previously been raised about acetaminophen's potential to increase the risk of neurodevelopmental disorders in children.
The analysis, published in JAMA Internal Medicine, examined electronic health records from January 2001 to December 2023. Researchers identified mother-child pairs where the mother had received an acetaminophen prescription. The study included 124,333 children, with an average age of nine, of whom 3,445 (2.8 percent) were diagnosed with autism. A separate group of 97,285 children, with an average age of seven, had 5,168 (5.3 percent) ADHD diagnoses. In both analyses, no association was found between prenatal acetaminophen use and these conditions, regardless of the trimester of use or frequency.
Researchers from the Hong Kong Hospital Authority emphasized that acetaminophen, also known as paracetamol in Europe, remains a safe and essential pain reliever and fever reducer during pregnancy. They warned that "unwarranted reluctance to use paracetamol could lead to undertreatment of pain and fever, or the use of more harmful alternatives, both posing risks to the pregnancy and developing fetus."
In contrast, a study from Copenhagen University Hospital in Denmark, published in Human Reproduction Open, investigated potential impacts on reproductive health. This study, involving 685 pregnant women and 302 infant daughters, found that infant girls exposed to acetaminophen in utero had significantly smaller ovaries, uteruses, and fewer ovarian follicles compared to those with no in-utero exposure. These changes were observed around the time of mini-puberty, a temporary surge of reproductive hormones in infants.
The Danish researchers also examined a separate cohort of 1,210 girls followed from infancy to adolescence. In this group, prenatal acetaminophen exposure was associated with smaller uteruses at puberty and smaller ovaries in adolescence.
Lead author Dr. Margit Bistrup Fischer noted that while animal studies suggest impaired ovarian follicle formation can lead to reduced fertility, it remains unknown whether the observed differences in human infants and adolescents have clinical significance for future fertility or age at menopause. She cautioned that mothers should not be alarmed, as the study identified associations rather than direct causation, and long-term follow-up is needed to determine the clinical significance of these findings.
The studies arrive as diagnoses for autism and ADHD continue to rise in the U.S. Current figures indicate that one in 31 U.S. children has autism, an increase from one in 150 in the early 2000s. ADHD diagnoses also show an upward trend, with seven million American children diagnosed in 2022, and significant increases in first-time diagnoses among adults aged 30-64 between 2021 and 2024.