In recent years, the number of patients suffering from allergic diseases has increased dramatically, and a wide range of anti-allergy drugs have appeared on the drug market. Patients often have the question in their minds, “Should I stick to one type of anti-allergy drug or change it?” People often refer to anti-allergy drugs as antihistamines. Since the first antihistamine was introduced in the 1940s, there have been different first-generation drugs in the market, including promethazine, hydroxyzine, dechloroxazine, paracetamol, doxorubicin, cerebrolysine, cycloheximide, ketotifen and so on. These drugs are absorbed orally through the stomach and intestines, and the effect starts in 30 minutes and lasts for 4 to 6 hours. After the 1980s, the second generation of antihistamines were produced, including astemizole, terfenadine, loratadine, cetirizine, imipramine, desloratadine and fexofenadine, etc. These drugs have little effect on the central nervous system and have no or only mild drowsiness. So, why should anti-allergy drugs be changed? First, different kinds of anti-allergy drugs have their own mechanism of action and anti-allergic properties, and various drugs have different focuses in the treatment of allergic diseases. For example, cold urticaria is effective with cycloheximide; fever urticaria is effective with Antares; for acute urticaria, you should choose anti-allergy drugs with fast onset of action; for chronic allergic diseases, because of the relatively long treatment time, you should choose some drugs without drowsiness and relatively small side effects, such as loratadine, imipramine or desloratadine. For chronic, persistent or severe acute allergic diseases, the simultaneous use of two or more anti-allergic drugs can increase the therapeutic effect, that is, the combination of drugs. When using drugs, it should be noted that the selected drugs should belong to different categories: it is appropriate to use drugs without sedative effects during the day, and apply drugs with sedative and sleeping effects after dinner or at bedtime. For those who need long-term combined medication, all medications should not be discontinued immediately after the condition is stabilized and symptoms are controlled, but should be withdrawn from one medication first and gradually discontinued, so as to reduce the relapse of the disease. Secondly, there is resistance to any kind of anti-allergy drug, and some patients who have been taking the drug for just one month have become extremely resistant to it, so it is necessary to continue treatment with a different anti-allergy drug.