Side effects of drugs, also called side effects, are other effects that occur when drugs are taken at normal doses and are not related to the purpose of the drug. These effects are originally part of their pharmacological action and are not necessarily all bad. For example, mirtazapine is an antidepressant drug with a sedative-hypnotic side effect, so we often use this side effect to improve the patient’s insomnia symptoms, thus killing two birds with one stone. So, side effects are not always a bad thing. Adverse drug reactions” refers to the application of drugs according to normal usage and dosage to prevent, diagnose or treat diseases, the occurrence of harmful reactions unrelated to the purpose of treatment, including side effects, toxic reactions, metabolic reactions, after-effects, secondary effects, idiosyncratic reactions and “three to “(carcinogenic, teratogenic, mutagenic) effects. Therefore, the harmful part of the drug side effects is the adverse reaction. Secondly, how high is the probability of adverse drug reactions? In the drug instructions, there are words such as “common adverse reactions”, “rare adverse reactions” and “rare adverse reactions”. Some patients and family members may understand: common means that a large proportion of people taking the drug will have an adverse reaction, rare means that a small proportion of people taking the drug will have an adverse reaction, and rare means that one or two percent of patients will have an adverse reaction. But in fact, these words on the drug’s instruction sheet do not mean this. The International Committee for Organization of Medical Sciences (CIOMS) recommends that the incidence of adverse reactions be expressed as: very common (≥10%), common (1% to 10% with 1%), occasional (0.1% to 1% with 0.1%), rare (0.01% to 0.1% with 0.01%), and very rare (<0.01%). In other words, a common adverse drug reaction means that out of 100 people taking this drug, a single-digit (1-10) number of patients will develop the condition referred to. Therefore, the probability of adverse reactions in the antidepressant drugs we are using now is relatively small, and they usually disappear gradually in the first week of taking the drug.