Asthma
There have been studies that show a link between acetaminophen (Tylenol) and asthma. For instance a 2008 analysis of information collected from a very large study called the International Study of Asthma and Allergies in Childhood, or the "Isaac study" for short, showed that children who had taken acetaminophen for a fever during the first year of their life had a 50% higher risk of getting asthma later on. The more acetaminophen children took the higher their risk of getting asthma. Children who took it once a month had threefold increase in their risk of getting asthma. An increase in asthma rates in multiple countries corresponded with increased sales of drugs which contained acetaminophen. Previously the American College of Physicians reported a link between non-atopic asthma and acetaminophen use based on results of  The Third National Health and Nutrition Examination Survey. Not all doctors are convinced of the link between acetaminophen and asthma.