Naproxen is a nonsteroidal anti-inflammatory drug (NSAID) used to treat pain, inflammation, and fever. Some common side effects of naproxen include:

Gastrointestinal symptoms: Naproxen can cause heartburn, nausea, vomiting, stomach pain, bloating, and diarrhea.
Central nervous system effects: Drowsiness, dizziness, headache, and confusion can occur with naproxen use.
Skin reactions: Some people may develop rashes, hives, or other skin reactions while taking naproxen.
Cardiovascular effects: Naproxen can increase the risk of heart attacks and strokes, especially in people who have existing heart disease or risk factors for heart disease.
Kidney problems: Naproxen can cause fluid retention, which can lead to swelling in the legs and ankles, and in severe cases, it can cause kidney damage.
Anemia: Long-term use of naproxen can lead to a decrease in the production of red blood cells, which can cause anemia.
Liver problems: Rarely, naproxen can cause liver problems, including hepatitis and liver failure.
It’s important to talk to your doctor about the potential side effects of naproxen and any other medications you are taking before starting treatment. If you experience any serious side effects while taking naproxen, it’s important to stop taking the medication and seek medical attention right away.