Prescription-strength naproxen is available as: 1  Naproxen 250 mg tablets. 2  Naproxen 375 mg tablets (immediate, delayed, and extended-release) 3  Naproxen 500 mg tablets (immediate, delayed, and extended-release)  Naproxen 125 mg/5 mL oral suspension -- one teaspoon (5 mL) contains 125 mg of 1  naproxen. Naproxen Sodium 275 mg tablets.