Doxycycline belongs to the class of medications known as tetracyclines. It is an antibiotic that is used to treat certain infections that are caused by bacteria. It is most commonly used to treat lung infections such as pneumonia and bronchitis, urinary tract infections such as cystitis, throat infections such as tonsillitis, skin infections, and sexually transmitted infections. This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here. Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If these effects are mild, they may go away within a few days or a couple of weeks. If they’re more severe or don’t go away, talk to your doctor or pharmacist. Call your doctor right away if you have serious side effects. Call 911 if your symptoms feel life-threatening or if you think you’re having a medical emergency. Serious side effects and their symptoms can include the following: Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this information includes all possible side effects. This information is not a substitute for medical advice. Always discuss possible side effects with a healthcare provider who knows your medical history. In some cases, they may not be available in every strength or form as the brand-name version.