Doxycycline is a common antibiotic often used for the treatment of various infections, such as bacterial infections, anthrax, malaria, and acne. Some examples of bacterial infections that can be treated with doxycycline include Lyme disease, gonorrhea, and plague. The medication is part of a class of drugs called tetracyclines, and works by decreasing bacteria's ability to make protein (which bacteria need in order to live). Among the factors that can affect the dosage of doxycycline your healthcare provider prescribes are the infection being treated, other medical conditions you may have, and other drugs you may be currently taking. While the medicine works best when taken without food, you may take it with food if it upsets your stomach. A few side effects of doxycycline include vomiting, loss of appetite, and yeast infections.