Flexon 400mg/325mg Tablet may cause side effects like nausea, vomiting, stomach pain, heartburn, dizziness, weakness, or skin rash. Consult your doctor if these persist or worsen. Although rare, seek immediate medical attention for severe side effects such as bloody urine, abnormal blood counts, or liver problems. Paracetamol rarely causes side effects when taken at the correct dosage. Consult your pharmacist or doctor if you notice anything unusual or experience a serious allergic reaction.