Hydrochlorothiazide belongs to the group of thiazide diuretics with diuretic and blood pressure-lowering effects, and is used clinically in the treatment of edematous diseases and hypertension. Its main hazards are water and electrolyte disorders, elevated blood glucose, elevated blood uric acid, and allergic reactions. 1. Water and electrolyte disorders: the most common are hyponatremia and hypokalemia. The main symptoms include dry mouth, irritability, fatigue, poor appetite, and even muscle cramps. Hypokalemia is also prone to cause cardiac arrhythmia. 2. Elevated blood glucose: Hydrochlorothiazide can inhibit the release of insulin, leading to reduced glucose tolerance and elevated blood glucose. 3. Elevated blood uric acid: hydrochlorothiazide acts on the renal tubules, can interfere with the excretion of uric acid, causing elevated blood uric acid, and even induced gout, so patients with hyperuricemia and a history of gout should be prohibited from using hydrochlorothiazide. 4. Allergic reaction: allergic reaction is relatively rare, may appear urticaria, skin itching and other symptoms, severe anaphylactic shock can occur. In order to avoid serious adverse reactions, hydrochlorothiazide must be used under the guidance of specialized physicians, strictly grasp the indications and contraindications.