Fatigue, dizziness, headache, nausea, and diarrhea are the most commonly reported side effects in patients. As the body adjusts to the medication, side effects will fade. Consult a local physician immediately if chest pain, fainting, or decreased sexual ability occur. Serious side effects can include vision changes, fever, and increased amount of urine. Allergic reaction is rare but can cause symptoms of swelling in the face, tongue, or throat. Laboratory tests should be performed throughout therapy to determine kidney function and levels of potassium in the blood. Schedule these tests with a physician if choosing to buy zestril online.