 <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 more often than directed. Do not take antacids containing aluminum and magnesium within 2 hours of taking this medication. These antacids can decrease the absorption of fexofenadine. Tell your doctor if your symptoms do not improve after 1 week, if they worsen, or if they occur with a fever.The side effects of Allegra-D 24 Hour Oral: Dizziness, trouble sleeping, nausea, or headache may occur. If any of these effects last or get worse, tell your doctor or pharmacist promptly. An empty tablet shell may appear in your stool. This effect is harmless because your body has already absorbed the medication. If your doctor has prescribed this medication, remember that 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. Tell your doctor right away if you have any serious side effects, including: fast/irregular/pounding heartbeat, shaking (tremor), mental/mood changes (such as anxiety, confusion, nervousness, restlessness), problems urinating. Get medical help right away if you have any very serious side effects, including: seizures. A very serious allergic reaction to this drug is rare. </s>