Tetracycline Side Effects. Common tetracycline side effects may include stomach cramps, diarrhea, skin reactions to sunlight, and fever. There are also some side effects that can indicate something serious. A few of these serious side effects of tetracycline include blurred vision, unusual headaches, and watery diarrhea. Some side effects that occur rarely (in less than 1 percent of people) include allergic reactions, hair loss, and irritation of the esophagus.