NSAIDs may also cause side effects, especially when used at higher than recommended dosages for long periods of time. Gastrointestinal side effects that may occur include bloating , diarrhea , constipation , irritation of the lining of the stomach, nausea or vomiting . NSAIDs may also affect kidney function and reduce how quickly blood flows through the kidneys. They may cause retention of sodium and water which can lead to edema and high potassium levels. Occasionally, they may cause more serious damage to the kidneys. See NSAIDs for other commonly reported side effects.