Tetracycline is an antibiotic intended for the treatment of bacteria-induced infections that is supposed to be taken regularly to provide for best effects and maximum efficiency. The following mild side effects are common, although only a few people will get them while taking tetracycline: trouble swallowing, diarrhea, vomiting, mild nausea, swollen tongue, swelling in your rectal or genital area, stomach upset, and sores inside your mouth. These side effects can be reported only if you notice they change in intensity and begin to bother you too much. Serious side effects are very rare, but you need to know they are still possible. Stop taking tetracycline and tell your doctor about any of the following serious side effects as soon as you get them: severe blistering, nausea and vomiting, blurred vision, dizziness, dark colored urine, flu symptoms, loss of appetite, red skin rash, confusion, fast heart rate, easy bruising, fever, chills, and urinating less than usual. Less serious side effects are a lot more common and may include sores inside your mouth, swollen tongue, trouble swallowing, stomach upset, swelling in your rectal or genital area, diarrhea, mild nausea, and vomiting. You do not have to report the mild side effects, since they are usually short-lived and are unlikely to interfere with your everyday activities.