Tetracycline, antibiotic drug used to treat various bacterial infections, including urinary tract infections, Rocky Mountain spotted fever, trachoma (a chronic eye infection), and gonorrhea. Tetracycline is also sometimes used to treat early stages of Lyme disease, acne, gum disease, and certain gastrointestinal ulcers. It works by interfering with the invading bacteria’s ability to form essential proteins, thereby halting their growth.

Tetracycline is available by prescription in capsule form, taken orally, and in a reconstituted powder solution, applied topically. Typical capsule dosages range from 1 to 2 g per day, taken in one to four doses, with a recommended maximum of 4 g per day. Unless this drug causes stomach upset, it should be taken on an empty stomach (one hour before or two hours after a meal) with a full glass of water. It should not be combined with milk or other dairy products. Tetracycline usually relieves symptoms after 48 hours of treatment, but it should be taken for the prescribed length of time to avoid recurrence of infection.

Patients with severe liver disease or pregnant or breast-feeding women should not take this drug. Patients with impaired liver or kidney function or with systemic lupus erythematosus should use tetracycline with caution.
Possible side effects include diarrhea, nausea, vomiting, skin rash, itching, light sensitivity, facial swelling, headache, blurred vision, chest pain, sore throat, difficulty swallowing, or in infants, a bulging soft spot on the head. Children may develop discolored teeth with long-term use.

Tetracycline may interact adversely with antacids and other common gastrointestinal medications, oral contraceptives, blood thinners, lithium, penicillin, isotretinoin, cholestyramine, and sucralfate.