To evaluate the effect of acetaminophen (Tylenol and other similar products) on asthma risk, Dr. R. Graham Barr, from the Columbia Presbyterian Medical Center in New York, and colleagues analyzed data from the Nurses Health Study, which has been following more than 120,000 women.
Although the study began in 1976, participants were first asked in 1990 about how often they took acetaminophen, which is known as paracetamol in some parts of the world.
During follow-up, 346 women were diagnosed with asthma, the researchers note in the American Journal of Respiratory and Critical Care Medicine.
As acetaminophen use increased, so did the risk of asthma. Compared with nonusers, women who took the drug on more than 14 days per month were 63 percent more likely to develop asthma.