Doxycycline is a broad-spectrum bacteriostatic agent, which can treat diseases caused by a variety of pathogens, but at the same time it also has certain side effects and hazards to several organs and systems of the human body, such as nausea and vomiting, dizziness, allergies and so on, and excessive dosage may also cause some damage to the liver and kidneys. 1. Digestive system: Doxycycline can cause digestive symptoms, such as anorexia, nausea, vomiting, diarrhea and so on. 2. Nervous system: it may lead to increased intracranial pressure and corresponding symptoms, such as dizziness, vomiting, and edema of the optic nerve papilla. 3. Blood system: Occasionally, hemolytic anemia, thrombocytopenia, neutropenia, etc. may occur. 4. Dental: It may be deposited in teeth and bones, leading to yellowing of enamel and poor development of teeth, therefore, it is prohibited for lactating women, pregnant women and children under 8 years old. 5. Skin: allergic reactions may occur, manifested as macular rash, erythema. 6. Liver and kidney function: excessive dosage may lead to liver and kidney function damage. Warm reminder: Always take the medication as prescribed by the doctor and monitor the use of the medication.