Doxycycline is a prescription drug that helps your body to fight off the infection by slowing down the growth of bacteria. This drug is not intended for the treatment of viral infections such as cold and flu. This medicine works by slowing down the production of protein necessary for the bacteria to survive and multiply. Without protein bacteria become weaker, making it possible for your immune system to fight off the infection. It's best to take doxycycline with a full glass of water. Only in case your stomach gets easily upset can you take this medicine with some food, as food can slow down the absorption of doxycycline.