The caffeine content is too low. Normal coffee drinks will have a refreshing effect and will not feel sleepy immediately. However, Zimeitang Macy's coffee drink has no reaction after drinking, which means that the caffeine content of the coffee drink is too low and ineffective, or the body has adapted to caffeine. Secondly, because of overeating or constant stress, the body is tired, and caffeine can't play a refreshing role. In addition, lack of exercise and sleep will also affect the effect of caffeine.