Tetracycline is a prescription antibiotic used to treat infections caused by the presence of bacteria in the body. If you have watery or bloody diarrhea this can be a sign of new infection in your body. Do not try to treat it on your own - make sure you call your health care provider first and described the situation. Keep taking tetracycline for as long as recommended by your health care provider. If you still have some of the medicine left and it's past its expiration period, throw it away, as otherwise you can have serious health effects after taking expired tetracycline. You can continue taking tetracycline and report the following serious side effects to your doctor: chills and body aches, blistering and red skin rash, loss of appetite, severe stomach pain, confusion, trouble breathing, easy bleeding and bruising, unusual weakness, blurred vision, flu-like symptoms, pale skin, fever, yellowed skin, peeling. Your doctor may then decide to lower your dosage or you will need to stop the treatment altogether.