Anaprox, also called naproxen, is a medication used to manage pain. Anaprox is a nonsteroidal anti-inflammatory drug (NSAID), which reduces inflammation in the body and helps to manage swelling and pain as well as improve range of motion. Anaprox is often prescribed to treat painful conditions such as rheumatoid arthritis, osteoarthritis, menstrual pain, and sometimes endometriosis pain. Anaprox for endometriosis can reduce pain caused by scarring of the endometrial tissue. Anaprox is a brand-name prescription drug, but naproxen is also available as a generic and over-the-counter. Anaprox may cause a number of side effects such as feeling drowsy, dizzy, or lightheaded; digestive problems including diarrhea, gas, and constipation; headaches; and trouble sleeping.