Which of the following medication side effects should be reported immediately?

Severe headache is a side effect that should be reported immediately because it could indicate a more serious underlying issue, such as hypertension or an adverse reaction to the medication. Unlike other side effects, a severe headache can be a sign that something is significantly wrong and may require prompt medical attention.

While dry mouth, dizziness, and rash can be uncomfortable and worth mentioning to a healthcare professional, they do not typically suggest an immediate risk to the patient's health. For example, dry mouth is a common side effect that may be manageable and often does not require urgent intervention. Dizziness can vary in severity and might be related to dosage or dietary factors, while many rashes may be benign or easily treated.

Understanding when to escalate concerns about side effects is crucial for ensuring the safety and well-being of patients. Recognizing severe symptoms, like a severe headache, helps in taking timely action that can prevent complications.