The intervention group had better knowledge of precautions related to taking additional acetaminophen ( usual care 18.2 % , 95 % confidence interval [ CI ] = 10.9 % to 25.5 % vs. intervention 38 % , 95 % CI = 28.3 % to 47.7 % ; difference = 27.6 , 95 % CI of difference = 21.5 to 33.7 ) and knowledge of side effects ( usual care median = 1 , interquartile range [ IQR ] 0 to 2 vs. intervention median = 2 , IQR = 1 to 2 ; p < 0.0001 ) .