Pure milk generally refers to pure milk, coffee with pure milk is generally not harmful, the two will not produce adverse reactions, but if excessive consumption may cause bloating, sleep disruption and other discomforts. Coffee is a beverage that contains protein, carbohydrates, caffeine and other nutrients. Pure milk also contains proteins, various vitamins, minerals such as calcium and other nutrients. Drinking coffee and milk together will not produce toxic substances, but can provide better nutrition for the body. People with lactose intolerance are advised to drink lactose-hydrolyzed milk. However, if consumed in excess, it may irritate the gastrointestinal tract, causing bloating, diarrhea and other uncomfortable symptoms. The caffeine in coffee can have an excitatory effect on the brain and nervous system, and excessive consumption may also affect sleep.