The question of whether the rise in autism diagnoses can be explained by exposures occurring in the womb, particularly from over-the-counter (OTC) medications or other environmental factors, is complex and multifaceted. Autism spectrum disorder (ASD) is understood to result from a combination of genetic predispositions and environmental influences, many of which can act during prenatal development.
During pregnancy, the developing fetus is highly sensitive to environmental exposures because this is a critical period for brain development. Various substances that a mother might be exposed to—including medications, chemicals, pollutants, and nutritional factors—can potentially influence neurodevelopment through several biological mechanisms. These include oxidative stress, DNA damage, epigenetic changes, and hormonal disruptions, all of which can alter how genes are expressed and how neural circuits form and function.
Oxidative stress is one key pathway. It occurs when harmful molecules called reactive oxygen species accumulate and damage cells, including neurons. Certain chemicals found in the environment or medications can increase oxidative stress, potentially interfering with normal brain development. For example, heavy metals like mercury and lead, pesticides, and some plasticizers have been shown to cause oxidative damage and disrupt neural connectivity.
Epigenetic changes are another important mechanism. These are modifications that affect gene activity without altering the DNA sequence itself. Environmental exposures during pregnancy can change DNA methylation patterns or histone modifications, which regulate gene expression critical for brain development. Such epigenetic disruptions may contribute to the risk of autism by impairing neural signaling and connectivity.
Hormonal pathways can also be affected by environmental agents. Some chemicals mimic or block hormones, which are vital for brain growth and differentiation. Disruptions in these pathways during pregnancy may influence the likelihood of neurodevelopmental disorders, including autism.
Regarding OTC medications specifically, while many are generally considered safe during pregnancy, some substances could pose risks if taken inappropriately or in high doses. For example, certain pain relievers, antihistamines, or supplements might have subtle effects on fetal development, but the evidence is not definitive. More commonly studied are prescription medications like valproate, which is known to increase autism risk when taken during pregnancy. The role of OTC drugs is less clear and requires further research.
Other prenatal factors linked to increased autism risk include maternal health conditions (such as diabetes), advanced parental age, prenatal stress, birth complications like prematurity or low birth weight, and exposure to air pollution or toxic chemicals. These factors may interact with genetic susceptibility to influence autism risk.
