Tetracycline is an antibiotic that fights bacteria in the body. Tetracycline is used to treat many different bacterial infections, such as urinary tract infections, acne, gonorrhea, chlamydia, and others.Tetracycline may also be used for other purposes not listed in this medication guide.etracycline is used to treat many different bacterial infections, such as urinary tract infections, acne, gonorrhea, chlamydia, and others. Tetracycline may also be used for other purposes not listed in this medication guide.