Doxycycline is a broad-spectrum bacteriostatic drug, but can act as a bactericide in high concentrations. Doxycycline belongs to the tetracycline class of antibiotic drugs, a bacteriostatic drug that can affect the synthesis of bacterial proteins by inhibiting the growth of peptide chains, and can be used to treat chlamydial infections, mycoplasma infections, rickettsial diseases, plague, cholera, brucellosis and other diseases. Adverse reactions: the use of doxycycline may cause vomiting, nausea, abdominal pain, diarrhea and other gastrointestinal adverse reactions, and may cause allergic reactions, long-term use of the drug may cause secondary infections. Contraindication: Doxycycline must be contraindicated in people with a history of allergy to tetracyclines. Precautions: Once secondary infection occurs with the drug, the drug must be stopped immediately and appropriate treatment must be given. Long-term use of the drug requires regular follow-up checks of liver function and blood counts. Individuals should not abuse doxycycline, should follow the doctor’s instructions for medication, to achieve rational and scientific use of drugs.