Paracetamol (acetaminophen or para-hydroxyacetanilide) is a widely used over-the-counter analgesic and antipyretic, and although it is generally considered safe, its use during pregnancy or early postnatal life has recently raised concerns due to potential effects on fetal and neonatal development.

In ongoing studies, about 51 % of women in the western part of the European Union reported using paracetamol during pregnancy, indicating the prevalence of this problem [1]. Already in 2021, a consensus statement supported by 91 scientists, clinicians and health professionals was published, warning against the use of paracetamol in the prenatal period because it may increase the risk of certain neurodevelopmental, reproductive and genitourinary disorders [2]. A meta-analysis by Barańska et al. [3], involving 330550 women and their offspring indicates a significant association between prenatal paracetamol exposure and the occurrence of asthma and wheezing in children.

Exposure to paracetamol in utero may also have other health and social consequences that impact the individual's later life. There is evidence of behavioral and motor changes observed in offspring exposed to the drug during fetal development. Several studies have shown a significant association between paracetamol use during pregnancy and a wide range of neurodevelopmental outcomes in offspring, including autism spectrum disorder, attention deficit hyperactivity disorder (ADHD), isolated speech disorders, attention and executive function deficits, communication and behavioral problems, and psychomotor development. Human studies have reported that prenatal exposure to paracetamol is associated with lower intelligence quotient (IQ) in children [4]. Language impairments and other behavioral disorders, such as oppositional defiance, have also been reported [2,5,6]. Importantly, long-term use, higher doses, and increased frequency of exposure were associated with a more pronounced relationship with the aforementioned neurodevelopmental outcomes [7]. Umbilical cord biomarkers indicate a dose-dependent association between fetal paracetamol exposure and a higher risk of developing ADHD and autism spectrum disorder in childhood [8].

Prenatal and early postnatal exposure to paracetamol has been associated with neurodevelopmental alterations, potentially via several mechanistic pathways. Drug is metabolized into reactive intermediates such as N-acetyl-p-benzoquinone imine (NAPQI), which can induce oxidative stress, disrupt mitochondrial function, and modulate monoaminergic neurotransmission in the developing brain, potentially interfering with critical processes such as neuronal proliferation, differentiation, and synaptogenesis [9]. The metabolism of paracetamol, including glucuronidation (the process by which a glucuronic acid molecule is added to the drug) and sulfonation (the addition of a sulfonate group), via enzymes such as uridine diphosphate-glucuronosyltransferases (UGTs) and sulfotransferases (SULTs), as well as oxidation through cytochrome P450 (CYP) pathways, varies with developmental stage and can be modulated by sex hormones [10].

This suggests that fetal and neonatal brain exposure to active metabolites of paracetamol may be sex-dependent, with differences in enzyme expression and hormonal regulation influencing the pharmacokinetics of the drug, potentially leading to differential effects between males and females [11]. It has been observed, that the effect of paracetamol on the occurrence of ADHD and borderline or clinical autism spectrum disorder may differ between male and female offspring, with symptoms being slightly more severe in boys. Male fetuses appear to be more sensitive to the neurotoxic effects of paracetamol, with a higher likelihood of developing attention and behavioral problems later in life [11].

The mechanisms underlying these sex-dependent effects are not yet fully understood, but may involve disruption of androgen-driven masculinization in males. Specifically, prenatal exposure to paracetamol may interfere with testosterone and prostaglandin signaling, both of which are crucial for normal male brain development and later behavior [12].

Animal studies further show that perinatal paracetamol exposure can lead to behavioral alterations and changes in oxidative stress markers in the brain, often in a sex-specific manner, with males and females exhibiting differential susceptibility [13]. Together, these metabolic, oxidative, and neurochemical mechanisms provide a biological framework for understanding observed sex-dependent effects, highlighting the role of hormones, enzyme activity, and differential maturation of monoaminergic systems in modulating the developing brain's sensitivity to paracetamol.

These observations are consistent with findings in other age groups. In adults, paracetamol is generally considered safe at recommended doses, but emerging evidence suggests that its efficacy and risk profile may differ between men and women. Observations in humans have shown that the mean half-life of paracetamol was shorter in women than in men, suggesting that women may metabolize paracetamol more rapidly [14]. Another study found that paracetamol glucuronide clearance was significantly higher in women at the time of delivery and significantly lower in the early postpartum period, compared to healthy volunteers not using oral contraceptives [15]. These results suggest that hormonal status may influence paracetamol metabolism (Tukur et al., 2021). Another study describing the sex-dependent effects of paracetamol is Court et al. [16]. The authors suggest that there are sex-related differences in the pharmacokinetics of paracetamol, including a lower metabolite-to paracetamol AUC (Area Under the Curve) ratio in women. This suggests that the drug may be metabolized differently between men and women.

Several studies have shown that women may experience stronger analgesic effects of paracetamol than men, but at the same time, women may be more susceptible to paracetamol-related adverse effects, particularly hepatotoxicity. In addition to differences in efficacy, studies suggest that paracetamol-induced acute liver injury and acute liver failure occur more frequently in women [17,18]. Liver damage after long-term or excessive paracetamol use may result from sex differences in liver enzyme activity and metabolic pathways [19,20].

This difference may be attributed to hormonal influences, particularly estrogen, which can modulate both pain sensitivity and hepatic drug metabolism [21]. Estrogen has been shown to regulate key liver enzymes involved in paracetamol metabolism, including UGTs, SULTs, and cytochrome P450 enzymes (CYP2E1, CYP3A4), as well as to influence glutathione levels, thereby affecting detoxification pathways, the formation of the toxic metabolite NAPQI, and ultimately the drug's pharmacokinetics and pharmacodynamics in women [22]. These combined effects may underlie sex-dependent differences in paracetamol toxicity, as heightened pain sensitivity could prompt higher intake and greater exposure to reactive metabolites. Several epidemiological studies support the notion that individuals with increased pain sensitivity may self-administer analgesics more frequently [23]. Furthermore, women tend to have a higher ratio of body fat to muscle mass compared to men, which may alter the distribution of lipophilic drugs such as paracetamol and contribute to differences in drug response [24].

As the animal models offer insight into the developmental impact of drug use during pregnancy and postnatally, the present study examined whether there are sex-specific effects of early paracetamol exposure on behavior and neurotransmission in rats. Although prenatal paracetamol exposure has been the subject of numerous studies, the sex-specific effects of early paracetamol use on monoamine levels, learning and association processes in offspring remain unclear. Given these findings, it seems reasonable to investigate whether early paracetamol use has sex-specific effects on motor skills and cognition in animals. This study fills a gap in neuropharmacological research examining sex differences in the consequences of prenatal and early postnatal exposure to paracetamol. Our findings contribute to the development of sex-specific neuropharmacology and may provide insight into the causes of neurobehavioral disorders associated with commonly used medications.