An adverse reaction is usually a side effect that is not related to the therapeutic purpose even after the drug is used in the prescribed dosage and usage. Such adverse reactions are usually to exclude drug overdose, drug usage errors and other drug use, as well as reactions formed by quality problems. Adverse drug reactions can usually include side effects, toxic reactions, allergic reactions, as well as idiosyncratic reactions and secondary reactions. For example, many drugs may cause gastrointestinal discomfort, such as nausea, acid reflux, diarrhea and other symptoms, which are usually mild and can be improved after stopping the drug. These side effects do not require special treatment. Other adverse reactions are mainly allergic reactions, such as penicillin allergy, which may result in rash, fever, chills and other manifestations, and can be improved after giving corresponding anti-allergic treatment. More serious adverse reactions may be the teratogenic effects of the drug, especially for women during pregnancy, and drugs that have teratogenic effects on the fetus should not be used. There are also carcinogenic effects or mutagenic effects, which are also more serious.