Doxycycline is an antibacterial drug of tetracycline class, which has good broad-spectrum bactericidal effect on gram-negative bacilli, gram-positive cocci, mycoplasma, chlamydia, and anaerobic bacteria. It is mainly used for infections caused by bacteria, such as typhoid, venereal disease, urethritis, tetanus, trachoma, and also for the treatment of acne, and the tablets can also be used as postoperative adjuvant therapy for patients with periodontitis. However, doxycycline is contraindicated in children under eight years of age because it can affect the development and growth of their teeth. Doxycycline is also contraindicated in pregnant women because it can enter the fetus through the placenta, causing discoloration of the fetus’ teeth and inhibiting the growth of the fetus’ bone marrow. Women who are breastfeeding should not restart breastfeeding until 5 days have elapsed if they are using doxycycline. It is important to drink plenty of water when taking doxycycline, otherwise it tends to irritate the esophagus and can cause ulcers. It is recommended to always drink plenty of water when taking doxycycline and to take a standing position. It is best to avoid lying down for 30 minutes after taking the drug.