SN instructed patient that Doxycycline is an antibiotic used in the treatment of a number of types of infections caused by bacteria and protozoa. Doxycycline can be used either by mouth or intravenously. Common side effect may include diarrhea, nausea, vomiting, a red rash, and an increased risk of a sunburn. Avoid combination of doxycycline with dairy, antacids, calcium supplements, iron products, and laxatives containing magnesium since these foods and supplements may decrease doxycycline's effectiveness.