Keep in mind that your doctor has prescribed this medication because he or she judged that the benefits of this medication outweigh the risk. Many people who use this medication do not have serious side effects, however, some side effects you may feel due to using losartan HCTZ are: Dizziness, Lightheadedness, Dehydration, Dry mouth, Muscle cramp, Weakness, Fast, slow, and irregular heartbeat Let your doctor know immediately if you undergo any of the unlikely but serious side effects: Fainting, Decrease in vision, Eye pain, Signs of kidney problem This product may even cause a loss of body water (severe dehydration). If that is the case, let your doctor know immediately if you undergo symptoms such as muscle cramps, dry mouth, irregular heartbeat, etc.