The common side effects often go away with time, but if they worsen or persist the patient should contact their physician. The common side effects of losartan potassium with hydrochlorothiazide include dizziness, stuffy nose, blurred vision, and lightheadedness. Serious side effects are unlikely, but they do occur. Patients who experience the serious side effects should contact their doctor immediately. The serious side effects include unusual thirst, reduced sexual ability, weakness, fainting, fast heartbeat, confusion, significant change in amount of urine, muscle pain, seizures, unusual fatigue, abdominal/stomach pain, dark urine, or yellowing of the eyes or skin. An allergic reaction is unlikely, but can occur. The signs include trouble breathing, rash, severe dizziness, itching, and swelling of the throat, face, tongue and lips.