Vasiclovir is used in the treatment of viral infectious diseases such as herpes zoster and herpes simplex, etc. It mainly has side effects and hazards in the digestive, neuropsychiatric, hematologic, urinary and cardiovascular systems. 1. Digestive system: mainly loss of appetite, stomach upset, abdominal pain, diarrhea, nausea, vomiting, etc., of which nausea and diarrhea are more common. 2. Neuropsychiatric system: mainly headache, dizziness, fatigue, etc., of which headache is more common. 3. Hematological system: Thrombocytopenic purpura, anemia, granulocytopenia, leukopenia, etc. may occur when taking valacyclovir. 4. Urinary system: some patients may have renal insufficiency or aggravation of renal dysfunction after taking vasiclovir. 5. Cardiovascular system: tachycardia, arrhythmia, etc. may occur in some patients. 6. Other: myalgia, ophthalmoplegia, photophobia, arthralgia and so on are also one of the side effects of vasiclovir. Valaciclovir is contraindicated in people who are allergic to the drug, pregnant women, and children under 2 years old. The incidence of side effects is not high, and they are generally mild, with a high overall safety profile. Patients are advised to consult their doctors, choose the drug according to their condition and personal needs, and take the drug as prescribed by the doctor.