Overnight coffee is not recommended to drink, in addition to overnight coffee can drink depending on the circumstances, mainly with whether it is stored properly, whether the coffee is deteriorating and other factors. First of all, overnight coffee can contain more tannins after being placed, and the substances in it will be oxidized, resulting in a relatively weaker refreshing effect and poor taste, therefore, it is still recommended that coffee is best to drink the day after brewing. Secondly, if properly preserved, not contaminated and not deteriorated can drink, for example, after boiling and brewing coffee, the coffee will be poured into a clean closed vessel, to be stored in the refrigerator after the temperature is not hot, to minimize the possibility of breeding bacteria, you can drink. If placed in a higher temperature, air humidity environment, and sealed improperly, it is easier to breed bacteria, and after reheating the nitrite component will relatively increase, so that coffee deterioration, drinking may produce certain damage to the body, such as nausea, vomiting, diarrhea, abdominal pain and other gastrointestinal symptoms, and even food poisoning. Therefore, such cases should not be drunk. In addition, some special groups of people need to pay attention to caution when drinking coffee, such as children, pregnant women, the elderly, and special groups of people suffering from stomach problems, heart disease, allergies to coffee, etc., to avoid aggravating the disease or other adverse effects on the body. At the same time, care should be taken to avoid drinking too much coffee, such as no more than 3 cups per day, as well as to avoid drinking strong coffee, which may cause discomfort. For those who want to refresh, it is recommended to develop good daily habits, reduce staying up late, avoid eating a lot before bedtime and strenuous exercise, etc., to ensure the quality of sleep.