Paracetamol (Tylenol) was first synthesized by an American chemist in 1877. Disputes about safety prevented it’s use for about eighty years, until a second look revealed that the accepted drugs of a similar chemical lineage actually served as precursors, which the body’s metabolism transformed into the active para-acetylaminophenol.
It was determined that contamination of materials used in testing the efficacy and safety of the then new painkiller, were most likely the culprit in painting a picture of side effects, toxicity, and carcinogenicity. If not for these missteps, the medication could have been made available nearly two decades before the introduction of aspirin to the market in the late 19th century.
As to aspirin’s safety, what of Reye’s Syndrome developed in connection with the treatment of symptoms, associated with viral infections? Children and young adults are the most frequently diagnosed with liver and brain injury in this case. Their immune response is different from the more mature adult exposed to health threats over a greater time period.
The body’s metabolism under viral attack perhaps is altered such that normally tolerated substances are treated in a different manner, and lead to a different outcome.