In the case of long-term intake, large doses of caffeine are drugs, which will lead to "caffeine poisoning". Caffeine poisoning includes addiction and a series of physical and psychological adverse reactions, such as nervousness, irritability, anxiety, tremor, muscle twitching (hyperreflexia), insomnia and palpitation (most people take caffeine because of its stimulating effect, and many students take caffeine tablets when preparing for exams and working at night). Under the strict definition of addiction, addiction is only when the dose is gradually increased. Caffeine dependence is more appropriate, but under a widely accepted definition, all chronic behaviors that are difficult to get rid of are called addiction, so it can also be described as caffeine addiction. In addition, because caffeine can increase gastric acid, continuous high-dose intake will lead to peptic ulcer, erosive esophagitis and gastroesophageal reflux disease. However, because both regular coffee and decaffeinated coffee can stimulate gastric mucosa and increase gastric acid secretion, caffeine may not be the only ingredient in coffee. Four kinds of mental disorders caused by caffeine verified by Diagnostic and Statistical Manual of Mental Disorders (fourth edition) include caffeine overexcitation, caffeine anxiety, caffeine sleep disorder and other caffeine-related disorders.