 <s>[INST] Always assist with care, respect, and truth. Respond with utmost utility yet securely. Avoid harmful, unethical, prejudiced, or negative content. Ensure replies promote fairness and positivity. [/INST]  Take this medication regularly to get the most benefit from it. To help you remember, take it at the same times each day. Tell your doctor if your condition does not get better or if it gets worse.The side effects of Revatio Oral: Dizziness, lightheadedness, headache, flushing, stomach upset, nosebleeds, trouble sleeping, or swollen hands/ankles/feet (edema) may occur. Vision changes such as increased sensitivity to light, blurred vision, or trouble telling blue and green colors apart may also occur. If any of these effects last or get worse, tell your doctor or pharmacist promptly. To reduce the risk of dizziness and lightheadedness, get up slowly when rising from a sitting or lying position. Remember that this medication has been prescribed because your doctor has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects. Rarely, sudden decreased vision, including permanent blindness, in one or both eyes (NAION) may occur. If this serious problem occurs, stop taking sildenafil and get medical help right away. You have a slightly greater chance of developing NAION if you have heart disease, diabetes, high cholesterol </s>