In addition to the therapeutic effect of the drug, sometimes there are some adverse reactions, the following are common: 1, allergic reactions: is some special physique (generally referred to as allergic) of patients with some special reactions to the drug. Most commonly seen in antimicrobial and biological products, such as penicillin, streptomycin, gentamicin, chloramphenicol, etc.; biological products, such as tetanus antitoxin, various vaccines, etc.. When allergic reactions occur, rash and drug fever may occur in mild cases, and shock and even death may occur in severe cases. Therefore, in the use of some drugs that can cause allergic reactions must be made allergy test. 2, side effects: that is, other than the therapeutic effect of other effects. For example, when treating gastrointestinal spasmodic abdominal pain with atropine, dry mouth and blurred vision can occur; when treating urticaria with fenagin, patients appear drowsy and weak. It is difficult to avoid these side effects because they occur simultaneously with the therapeutic effect when applying the usual amount. 3. Toxic reactions: are harmful reactions to the human body that occur when the dose of the drug is too large or the duration of the drug is too long, or when the sensitivity of the human body is high. For example, sulfonamides can cause hematuria; streptomycin, kanamycin and neomycin can cause dizziness, tinnitus and deafness; heparin and chloramphenicol can cause aplastic anemia and leukopenia; neomycin and tetracycline can also cause damage to liver and kidney, etc. 4, dependence and addiction: often take certain drugs, such as codeine, sleepytone, etc., will cause dependence or addiction to drugs, after stopping use can produce a series of psychological and physical adverse reactions. Another example is the long-term use of painkillers, Remifentan p-aminosalicylate sodium is prone to dependence, making the drug less effective.