Learn about the side effects of naproxen, from common to rare, for consumers and healthcare professionals. Naproxen is a painkiller that helps relieve pain and reduce swelling (inflammation). You can buy some types from pharmacies, but others are only available with a prescription. Naproxen is a type of painkiller called a non-steroidal anti-inflammatory drug (NSAID). Overview: Naproxen is a nonsteroidal anti-inflammatory drug (NSAID) used to relieve pain, reduce swelling, and lower fever. Common side effects include belly pain, upset stomach, heartburn, or. Naproxen is used to treat a variety of inflammatory conditions and symptoms that are due to excessive inflammation, such as pain and fever (naproxen has fever-reducing, or antipyretic, properties in addition to its anti-inflammatory activity). [10] Naproxen is a nonsteroidal anti-inflammatory drug (NSAID). It works by reducing hormones that cause inflammation and pain in the body. Naproxen is used to treat pain or inflammation caused by conditions such as arthritis, ankylosing spondylitis, tendinitis, bursitis, gout, or menstrual cramps. Learn about side effects, dosage, uses, and more for naproxen, which is a generic prescription oral tablet that treats many conditions, such as arthritis. Naproxen is a nonsteroidal anti-inflammatory drug (NSAID) used to relieve symptoms of arthritis (eg, osteoarthritis, rheumatoid arthritis, or juvenile arthritis) such as inflammation, swelling, stiffness, and joint pain.