Most medications can cause side effects which can be defined as an unwanted response to a medication when it is taken in normal doses. Side effects can range from mild or severe, temporary or permanent. Side effects are not experienced all patients who take this medication. Many side effects can be managed, and others may go away over time. Common side effects may include burning of the eyes or stinging, itchy eyes, dry eyes and dizziness. Serious side effects may include swelling or redness of your eyelids, eye redness, pain, discomfort, or sensitivity to light, drainage, crusting, or oozing of your eyes or eyelids, wheezing, gasping, or other breathing problems, swelling, rapid weight gain, feeling short of breath or even with mild exertion. Get emergency medical attention if you have any signs of an allergic reaction (hives; difficulty breathing; swelling of your face, lips, tongue, or throat). Stop using COSOPT immediately and call your doctor at once if you experience any of the above noted serious side effects. This is not a complete list of side effects and others may occur. Call your doctor for medical advice about additional side effects.