The incidence of ASD began to increase in the early 1980s, coinciding with the increase in APAP use after aspirin was associated with Reye’s syndrome. The ratio of regressive to infantile ASD also rose at the same time.

The popularity of APAP use and the prevalence of ASD was substantially higher in Denmark than in Finland in the mid-2000s.

The incidence of ASD has steadily increased as direct-to-consumer advertising, marketing of over-the-counter medications, and perhaps other factors such as mandated use of APAP with the MenB vaccine (see discussion) have led to increased APAP exposure early in life.

Factors other than the move away from aspirin and advertising have led to increasing use of APAP that corresponds to increasing levels of ASD. For example, many parents use APAP to avoid or treat adverse reactions to vaccines, and the vaccine schedule has dramatically increased since 1980. In addition, use of APAP during labor and delivery and in the NICU have increased as a result of APAP use for ERAS protocols developed to reduce opioid exposure after the opioid pandemic of the 2010s.

Numerous investigators noted a very low prevalence of ASD prior to 1970 or noted increases in the prevalence of ASD that could not be attributed to factors other than a real increase. 

Studies in several countries with chronic shortages of medication found dramatically lower-than-expected levels of ASD relative to other developmental issues, including Down syndrome.