Research shows that taking Tylenol during pregnancy is NOT linked to autism or ADHD, but may affect future fertility

Acetaminophen use during pregnancy is not linked to autism or ADHD, although it may lead to future fertility problems, a pair of studies suggests.

Acetaminophen, the active ingredient in Tylenol, is the only over-the-counter pain reliever and fever reducer recommended for pregnant women because alternatives such as ibuprofen are linked to birth defects.

However, the drug has sparked controversy in the past few years over claims that it may increase the risk of children being born with neurodevelopmental disorders such as autism.

In a new analysis of medical records of more than 120,000 children over two decades, researchers disputed these claims. The team found that exposure to acetaminophen, called paracetamol in Europe, during pregnancy was not associated with an increased risk of being diagnosed with autism.

Additionally, data from an additional 100,000 children showed no increased risk of ADHD diagnosis in children born to mothers who used acetaminophen during pregnancy.

The researchers warned that mothers who skip acetaminophen doses to treat fever or severe pain could prompt them to use unsafe alternatives or develop complications such as birth defects, premature birth and miscarriage.

However, a second study from Denmark found that girls whose mothers took acetaminophen during pregnancy had smaller ovaries, smaller uteruses, smaller ovarian follicles, and lower levels of reproductive hormones in infancy.

The team noted that these changes could lead to fertility problems later in life, although they cautioned that mothers “should not worry” and should discuss acetaminophen use with their doctor.

A pair of studies have found that while acetaminophen is not linked to autism or ADHD, it may increase the risk of fertility problems in offspring later in life (file photo)

Two studies show that autism now affects one in 31 children in the United States, up from one in 150 in the early 2000s.

Experts are still figuring out the specific reasons for the rise in cases, although they suggest it may be related to increased awareness and screening, as well as potential environmental issues.

ADHD is also on the rise in the United States among both children and adults. Seven million American children were diagnosed with a neurodevelopmental disorder in 2022, up from six million in 2016, according to the latest data from the Centers for Disease Control and Prevention.

Recent data from Yale University also shows that between 2021 and 2024, newly diagnosed ADHD rose by 61 percent in adults ages 30 to 44 and by 64 percent in adults ages 45 to 64.

In the Chinese study, published in JAMA Internal Medicine, researchers examined electronic medical records to identify pregnancies in which the mother received a prescription for acetaminophen, and then created a cohort of mother-child pairs from January 2001 to December 2023.

Acetaminophen is usually available over the counter, but higher doses can only be obtained with a prescription.

The team studied 124,333 children (almost evenly split between men and women) and assessed them for an autism diagnosis. On average, the children were nine years old. There were 3,445 autism diagnoses in this group, representing a rate of 2.8 percent.

The ADHD analysis included 97,285 children aged an average of seven years, split equally between males and females. Among this group, there were 5,168 ADHD diagnoses, representing a rate of 5.3 percent.

Women who took acetaminophen during pregnancy were more likely to be older, have preexisting conditions such as psychiatric disorders, and more common signs of use such as infection, fever, or chronic pain, compared with those who were not prescribed the drug.

Acetaminophen is the active ingredient in Tylenol and other common over-the-counter cold, flu and pain relievers. This is the only recommended pain reliever and antipyretic drug for pregnant women.

Researchers found no link between prenatal acetaminophen use and autism or ADHD. There was also no difference in taking the drug in a particular trimester or at different frequencies, such as intermittently or daily. The advanced age of the mother and pregnancy in women over 35 also did not play a role.

“Paracetamol remains a safe and essential analgesic” [pain reliever] and antipyretic [fever reducer] during pregnancy, while alternatives such as NSAIDs and opioids carry well-documented risks,” wrote researchers from the Hong Kong Hospitals Authority.

“Unjustified reluctance to use paracetamol can lead to undertreatment of pain and fever or the use of more harmful alternatives, which poses risks to pregnancy and fetal development.”

The authors also noted that mothers should evaluate acetaminophen use under the guidance of a physician.

In the second study, published in the journal Human Reproduction Open, researchers from Copenhagen University Hospital examined 685 pregnant women without any pre-existing conditions who were enrolled in the first trimester of pregnancy, as well as 302 young daughters.

Participants visited the testing center three times during the study: during the first trimester, third trimester, and screening when the children were three months old.

Around this time, babies experience mini-puberty, a surge of reproductive hormones caused by a temporary awakening of the reproductive system. This usually resolves within a few months or up to one to two years.

Newborn girls have high levels of follicle-stimulating hormone (FSH) and estradiol (estrogen), which control the development of eggs, regulate the menstrual cycle and stimulate ovulation.

Pregnant women in the study completed questionnaires every two weeks about their use of pain medications such as acetaminophen. The infant girls had ultrasounds to assess the size of their reproductive organs and blood tests to measure hormone levels.

The researchers also studied a separate group of 1,210 girls who were followed from infancy to adolescence and whose mothers reported acetaminophen use in the third trimester of pregnancy.

The team found that three-month-old girls exposed to the drug in utero had on average 40 percent less ovarian volume, 13 percent less uterine volume and 23 percent fewer ovarian follicles. Those exposed in the first trimester also had lower levels of anti-Mullerian hormone, which serves as a marker of ovarian function.

In a group of older girls, those exposed to acetaminophen in utero were more likely to have smaller uteruses at puberty and smaller ovaries during adolescence.

“Animal studies have shown that impaired ovarian follicle formation can lead to decreased fertility and earlier reproductive aging,” said Dr. Margit Bystrup Fischer, lead author of the study and a researcher in the Department of Growth and Reproduction at Rigshospitalet in Denmark.

“It remains unknown whether the differences observed in our study influence fertility and age at menopause in humans, and this will require long-term follow-up of the girls in our cohort.”

However, she cautioned that women who used acetaminophen during pregnancy “should not be alarmed by our results” because the study found associations rather than direct causation, and the results for individual women and children are unclear.

“It is important that our study does not evaluate [acetaminophen] causes reproductive problems, and provides no evidence that prenatal exposure affects future fertility or age at menopause,” she said.

“Although we observed similar associations in an independent cohort, long-term follow-up is needed to determine whether these early differences have any clinical significance later in life.”