This is a bit more anecdotal than I would prefer, but school level chemistry questions/experiments fairly consistently suggest that OTC aspirin tablets are arou

This is a bit more anecdotal than I would prefer, but school level chemistry questions/experiments fairly consistently suggest that OTC aspirin tablets are around 85% pure. e.g. https://uk.answers.yahoo.com/question/index?qid=20100817044954AAEu0Oz&p=mass%20of%20an%20aspirin%20pill https://uk.answers.yahoo.com/question/index?qid=201008170449... This is mostly deliberate, but acetic acid is a common contaminent in the manufacturing process.